obesity reviews

doi: 10.1111/obr.12161

Obesity Prevention

The effect of obesity prevention interventions according to socioeconomic position: a systematic review A. Beauchamp1,2,3, K. Backholer1,2, D. Magliano1,2 and A. Peeters1,2

1

Baker IDI Heart and Diabetes Institute,

Melbourne, Victoria, Australia; 2Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia; 3Population Health Strategic Research Centre, Deakin University, Melbourne, Victoria, Australia

Received 15 October 2013; revised 1 January 2014; accepted 2 January 2014

Address for correspondence: Dr. A Beauchamp, Obesity and Population Health, Baker IDI Heart and Diabetes Institute, Commercial Rd, Melbourne, Vic 3004, Australia. E-mail: [email protected]

Summary Obesity prevention is a major public health priority. It is important that all groups benefit from measures to prevent obesity, but we know little about the differential effectiveness of such interventions within particular population subgroups. This review aimed to identify interventions for obesity prevention that evaluated a change in adiposity according to socioeconomic position (SEP) and to determine the effectiveness of these interventions across different socioeconomic groups. A systematic search of published and grey literature was conducted. Studies that described an obesity prevention intervention and reported anthropometric outcomes according to a measure of SEP were included. Evidence was synthesized using narrative analysis. A total of 14 studies were analysed, representing a range of study designs and settings. All studies were from developed countries, with eight conducted among children. Three studies were shown to have no effect on anthropometric outcomes and were not further analysed. Interventions shown to be ineffective in lower SEP participants were primarily based on information provision directed at individual behaviour change. Studies that were shown to be effective in lower SEP participants primarily included community-based strategies or policies aimed at structural changes to the environment. Interventions targeting individual-level behaviour change may be less successful in lower SEP populations. It is essential that our efforts to prevent obesity do not leave behind the most disadvantaged members of society. Keywords: Intervention, obesity, prevention, socioeconomic inequalities. obesity reviews (2014) 15, 541–554

Introduction In most developed countries, there are socioeconomic gradients in obesity whereby the greater the degree of socioeconomic disadvantage, the higher the risk of being overweight and obese (1–3). Given the increasing prevalence of obesity (4) and its contribution to chronic conditions (5,6), this gradient will potentially result in wider inequalities in chronic disease in the future. In this context, it is essential to consider the potential impact of obesity

© 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

prevention interventions on socioeconomic inequalities in obesity (7,8). There is evidence that preventive activities can have varying impacts on different socioeconomic groups within a population. For example, mass media campaigns for smoking cessation and folic acid supplementation have been shown to be less effective in disadvantaged groups (9–11). However, whether interventions for the prevention of obesity have differential effects by socioeconomic position (SEP) has rarely been studied (12,13). Public health 541 15, 541–554, July 2014

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strategies to prevent obesity are increasingly being implemented, and it is imperative that their potential impact on socioeconomic inequalities in obesity is clearly understood (12). This will enable both the prioritization of strategies least likely to widen inequalities, and the implementation of targeted interventions to accompany those strategies shown to be less effective in lower socioeconomic groups. There are a number of potential reasons why a health intervention might differentially impact upon SEP groups within a given population. Lower SEP groups may face more structural barriers to healthier lifestyles such as limited financial resources (14,15) or neighbourhoodrelated factors (16,17). Interventions that do not address these underlying barriers (such as interventions based on information provision only) may have less success among lower compared with higher SEP groups (18). Conversely, ‘radical’ interventions that attempt to change the context or circumstances in which behaviour occurs might be more effective among lower SEP groups because they potentially address underlying structural barriers (18,19). Other possible factors leading to differential intervention effects could include the duration of the intervention, its potential for sustainability and its ability to reach all socioeconomic groups indiscriminately. The latter may be influenced by the reach of the intervention, as determined by the size of the target group of the intervention and the setting in which it is executed. This review aims to identify public health interventions for the primary prevention of obesity that report their effect on anthropometric outcomes by socioeconomic strata, to summarize the effectiveness of these interventions across the socioeconomic spectrum and to identify common attributes of interventions that may be most likely to benefit all SEP groups. A narrative review will be presented as studies are expected to have heterogeneous design features and variable outcome measures.

obesity reviews

Methods Search strategy Primary studies were identified by searching the following academic databases: Medline via OVID, EMBASE, CINAHL, EBM reviews, SCOPUS, Cochrane collaboration, Cochrane Public Health Group and Evidence for Policy and Practice Information Centre. We also searched grey literature sources, including the System for Information on Grey Literature in Europe, the Virtual Library for Public Health, Google Scholar, plus websites from relevant organizations. Search terms included keywords and Medical Search Headings terms for SEP, combined with terms for anthropometric outcomes, public health interventions and intervention studies. Specific search terms included Medical Search Headings terms found in relevant articles and reviews (12,13,20,21) (Table 1). There were no date restrictions on these searches (search undertaken September 2012). The reference lists of all relevant research and review articles were also scanned to capture any citations missed by electronic searches.

Study selection and inclusion criteria Included studies were independently assessed for their relevance by two reviewers with disagreements resolved through discussion among all four reviewers. Only Englishlanguage studies were included. We included results derived from public health interventions that utilized any type of study design to report changes in anthropometric outcomes stratified by a measure of SEP, or that reported an interaction term between SEP and an anthropometric outcome. We aimed to include primary prevention strategies that potentially address everyone across the socioeconomic gradient, rather than selective interventions that specifically

Table 1 Specific search terms Hedge term

Search terms

Socioeconomic position

Socioeconomic factors, social (class, hierarchy, inequalities), socioeconomic (status, gradient), townsend deprivation, Carstairs index, index of multiple deprivation, social or minority groups, poverty areas, health disparities, health inequalities, educational (status, attainment), employment (status, grade), manual labor, occupation, blue collar, workplace, unemployment, income, medical indigency, medically uninsured, Medicaid, poverty, deprivation, residence characteristics, public housing

Anthropometric outcomes

Obesity, overweight, weight (gain, control, maintenance) body mass index, body weight, adiposity, anthropometric, fat mass, skinfold thickness, waist circumference, waist hip ratio

Public health interventions

Obesity (prevention, control), health (promotion, behaviour, knowledge, education), policy (social, school, food, public, urban, environmental), environment (built, social, physical, urban), urban planning, neighbourhood, community, societal, intervention (social, community), exercise, tax, subsidies, price, social marketing, advice or counseling (diet, exercise, lifestyle, behavioural, weight management), school, workplace, campaign, food (labels, advertising)

Intervention study

Evaluation, effectiveness, intervention, randomised controlled trial, randomised, non-randomised, quasi experimental, pre-test, post-test, before and after studies, time series, repeat measures, repeat cross-sectional, follow-up studies, pilot studies, community trial, population or community (intervention, prevention, policy, program).

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© 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

obesity reviews

Obesity prevention and socioeconomic position A. Beauchamp et al.

target lower SEP groups (22). Accordingly, included studies were those aimed at the entire population, or those that were community-wide, or those aimed at individuals and groups of people within a society, community or organization. Interventions directed at particular ethnic, socioeconomic or otherwise minority groups were excluded, unless the study results were stratified by a measure of SEP. Studies of surgical or medication-based interventions were not included. We restricted our review to interventions aimed at primary prevention of weight gain, rather than interventions that specifically targeted weight loss in overweight/ obese populations. Given that many of the studies were community-based, they naturally included a proportion of overweight and obese participants; however, as long as the primary aim was prevention of weight gain, these studies were considered to meet the inclusion criteria. In children, this criterion was expanded to include studies with a primary goal of preventing further weight gain in overweight/obese children.

Data extraction and quality appraisal We developed a standardized data extraction form based on the PICOCS framework (Participants; Intervention; Comparison; Outcomes; Context; Study design) used for systematic reviews of the impact of public health interventions (23). Data on the following variables were extracted: sampling and inclusion criteria, baseline characteristics, intervention characteristics and mode of delivery, any comparison interventions received, anthropometric outcomes (both overall and by SEP strata), the context in which the intervention was delivered and the study design. The methodological quality of studies was assessed using the Effective Public Health Practice Project Quality Assessment Tool (24). This tool has been found to be adaptable to public health interventions (25,26). Quality appraisal and data extraction were conducted by two independent reviewers, with differences resolved through discussion with a third reviewer. Criteria used to assess the methodological quality of trials were selection bias, study design (including randomization), control for confounders, data collection methods and the reporting of withdrawals and drop-out. Blinding was not used as a criterion as this was considered not relevant to the majority of public health interventions reviewed. The Effective Public Health Practice Project Quality Assessment Tool asks between two and four questions for each criterion, with three to four possible options for each. For example, for the criterion ‘data collection methods’, the two questions are: (i) Were data collection tools shown to be valid? (ii) Were data collection tools shown to be reliable? Possible options for each question were ‘yes’, ‘no’ or ‘can’t tell’. Studies for which the answer was ‘no’ or ‘can’t tell’ to both questions were given © 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

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a weak rating for quality of execution in that criterion. Studies were reported as weak (those with at least two out of five weak ratings), moderate (one weak rating) or strong (no weak ratings) depending on the degree to which they met the quality criteria.

Analysis Studies demonstrating an overall effect on anthropometric outcomes were initially categorized according to whether they were effective or not effective among lower SEP groups. Within these categories, we then analysed studies to identify common characteristics between interventions, including the degree to which they addressed structural barriers to behavioural change; as noted earlier, particular structural barriers may be more or less prevalent among different SEP groups in a population. Studies were categorized as: low = non-structural interventions that target an individual’s intent to actively modify their behaviour; moderate = those that are less superficial, incorporating some change to policy or the structural environment to support behaviour change; high = radical interventions that attempt to significantly alter the environment in some way, thus minimizing individual choice or intent to modify behaviour. Finally, we performed a sensitivity analysis to evaluate findings only in those studies of medium or high methodological quality.

Results The literature search yielded a total of 3,634 articles, of which 154 were identified as potentially eligible. We finally included 15 papers in this review, representing 14 studies (Fig. 1). Reasons for excluding full-text articles are shown in Fig. 1.

Overview of included studies A summary of included studies are presented in Table 2. Date of publication ranged from 1997 to 2012. Of the 14 included studies, there were five randomized controlled trials (RCT). Five studies used a quasi-experimental nonRCT design, two were of cohort design and two were repeated cross-sectional surveys. All 14 studies were set in developed countries, with five conducted in the USA, two in the Netherlands, four in France, two in Germany and one in Australia. Nine studies were conducted among children (age range 3–12 years at baseline) and five were conducted among adults. Sample sizes were generally large with 10 studies having sample sizes of over 1,000 (range = 70 to 340,000). Two studies of overweight/obese children were included as their primary aim was prevention of further weight gain.

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Total number of Ɵtles idenƟfied in electronic searches n=3,634

Excluded as not relevant on Ɵtle and abstract review n=3,480

Full-text arƟcles reviewed n=154 IdenƟfied on reference list n=2 n=141 full-text arƟcles excluded as not meeƟng inclusion criteria Reasons for exclusion based on reading full text Anthropometric outcomes not reported n=16 Not reported by SEP n=100 Non-English manuscript n=8 Not weight gain prevenƟon n=6 No intervenƟon or follow-up n=10 Targeted ethnic group n=1 Final inclusion n=14 studies (n=15 arƟcles)

A variety of different indicators were used to measure SEP with most studies using one indicator only. For studies targeting children, indicators included parent’s education, occupation, income or social class (the latter not defined), neighbourhood or eligibility for subsidized school meals. Among adults, studies used occupation, education, income or area-based measures. Of the 14 included studies, seven reported an inverse socioeconomic difference in weight prior to the intervention, whereby lower socioeconomic groups were more likely to be of higher weight compared with their more advantaged counterparts. Most reported this as a difference in the baseline prevalence of overweight or obesity, although one study (27) reported this by mean body mass index (BMI). Six studies did not report baseline weight or prevalence of overweight and/or obesity by SEP, and one study from France found that pupils from kindergartens in privileged areas had higher BMI z-scores than did those from kindergartens in underprivileged areas (28). The duration of interventions ranged widely. Three studies implemented interventions of between 2 and 24 weeks duration, eight of between 1 and 5 years and three implemented ongoing interventions with evaluations at 4–7 years. Settings for the delivery of interventions also varied. One study was conducted nationally, five studies were community-wide (four of these included schools), and three were in schools only with two of these taking a school-wide approach and one targeting students within one school year only. Of the remaining five studies, one was conducted in a workplace, one at a community health centre, and three in a home setting, targeting either the individual or the family. The primary outcome was change

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Figure 1 Process of article selection.

in BMI for nine studies and change in the prevalence of overweight/obesity for the remaining five. Of the 14 studies, three reported no statistically significant overall effect of the intervention on any anthropometric outcome, or for any of the SEP subgroups analysed; one of these was among children (29) and two among adults (30,31). These were not further analysed.

Critical appraisal of included studies Of the 11 studies demonstrating an effect on anthropometric outcomes, five were rated as being of weak quality (27,32–36). This rating was most commonly given because of probable selection bias due to either the sampling method used or a low response rate. Other reasons were a high attrition rate from observational studies and limited description of control for potential confounders during analysis. Of the remaining six studies, two were rated as strong (37,38). The three studies showing no effect on anthropometric outcomes received moderate to strong ratings in terms of study quality (29–31).

Studies reporting no beneficial effect among lower socioeconomic position groups A total of five studies reported no beneficial effect among lower SEP participants, although all reported a benefit in higher SEP groups. One study targeted adults attending a chronic disease prevention programme at community health centres in the USA (32). While each programme had a unique curriculum, all focused on nutrition, physical © 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

Sampling and inclusion

Participants

© 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

Wang et al. (29) Design: Quasi-experimental Aim: To examine weight/ glycaemic outcomes in chronic disease prevention

Chomitz et al. (35) Design: cohort Aim: to assess a community intervention on child weight gain

Czernichow et al. (39) Design: Repeat cross-sectional population survey Aim: Assess obesity trends by SEP during NNP

Plachta-Danielzik et al. Design: Quasi-RCT Aim: To evaluate outcomes of school-based intervention on weight status

Recruitment: Health fairs, flyers, provider referrals Inclusion: In a chronic disease prevention programme Sample: Baseline n = 2,304 (67% of eligible); 6 months = 50%. No SEP differences in attrition

Recruitment: Not reported Inclusion: Students from kindergarten 5th grade ≥5 years old at baseline; no special needs Sample: n = 1,858 (52% of eligible) at follow-up. No SEP differences in attrition.

Recruitment: All people attending free national medical examination 1995–2005 Inclusion: aged ≥20 years Sample: n = 339,882 adults (1.4% of French population). No attrition

and Plachta-Danielzik et al. (33,34) Recruitment: Not clear Inclusion: Willingness to participate, first grade at school Sample: Baseline = 4 997; 4-year follow-up = 1,764 (35% of initial population); 8-year follow-up = 1,192 (24% of initial population). Drop outs more likely to be lower SEP than participants (18.9% vs. 40.0% respectively)

Interventions showing no effect in lower SEP groups Langnase et al. (27) Design: Recruitment: recruited from KOPS Quasi-experimental Inclusion: BMI ≥ 90th percentile Aim: To examine Sample: Baseline and follow-up: effect of SEP on Intervention group n = 26 long-term overweight/obese children; outcome of Non-intervention group n = 26 family-based overweight/ obese; Reference group intervention n = 26 normal weight. No attrition

Study design/aim

Table 2 Description of included studies

Sex: 78% women Age: 32% ≤ 45 year, 18% ≥ 65 years Anthropometrics: 60% had BMI ≥30 SEP: Education, employment, income

Sex: 48% girls Age: mean (SD) 7.7 (1.8) years Anthropometrics: 16.8% overweight (≥85th–< 95th percentile, 20.2% obese (≥95th percentile) SEP: Family income

Sex: 50% men; Age: Mean (SD) 42 ± 10 years Anthropometrics: 6.9% men, 6.4% women had BMI ≥30 kg m−2 SEP: Occupation

Sex: Intervention group = 48.7% male; non-intervention group = 50.3% Age: Intervention group median 6.3 year (5.9–6.5); non-intervention group = 6.3 (6.0–6.5) years Anthropometrics: Intervention group = 3.8% obese (≥97th percentile), 7.0% overweight (≥90th–< 97th percentile); non-intervention group 3.9% obese, 5.2% overweight SEP: Parent’s years of education

Sex: not reported Age: median (IQR) = 6.6 (1.9) years; Normal weight = 6.4(0.5) years; Anthropometrics: In non-reference group, 50% overweight (BMI ≥90th–< 97th percentile), 50% obese (BMI ≥ 97th percentile) SEP: parent’s education level

Baseline characteristics

Description: Included exercise, education and home visits delivered by community care workers to groups or individually Duration: 5 to 24 weeks

Description: Included city-wide healthy lifestyle campaigns, community-based fitness campaigns, school-based activities led by nutritionists; family outreach Duration: 3 years

Description: National nutrition guidelines, mass media campaigns Duration: Programme implemented in 2001, last data collection in 2005

Description: Diet and activity messages delivered by a nutritionist. Involved parents and teachers. Duration: Six nutrition sessions over 2 to 3 weeks within first school year

Description: Counselling on diet and activity at the family’s home, delivered by nutritionist Duration: Five sessions over 5 to 10 weeks. One session = 45 to 90 min

Intervention

Randomization: N/A Control intervention: No control group, participants were their own controls

Randomization: N/A Control intervention: None

Randomization: N/A Control intervention: None

Randomization: Schools randomly assigned every year over 6 years Control intervention: ‘intervention schools’ alternated to ‘non-intervention’, acting as control group

Randomization: N/A Control intervention: Reference group given healthy messages

Comparison group

Outcome: Improvement in BMI and glycaemic control Follow-up: Programme end and 6 months later Overall result: 18% showed weight loss at programme end; 28% at 6 months SEP results: Higher-income more likely to achieve weight loss than lower income at programme end but no difference by SEP at 6 months

Outcome: Change in BMI z-score Follow-up: End of intervention Overall result: Significant decrease in BMI z-score following intervention SEP results: Significant decrease in BMI z-core and obesity prevalence for high income but not low-income groups

Outcome: Abdominal adiposity Follow-up: Ongoing Overall result: 6.9% of men and 6.4% of women were obese in 1995 and 8.9% and 8.6% in 2005 respectively SEP results: Obesity prevalence regression slopes increased between 1995 and 2005 in all SEP categories except managers (men and women) and office workers (men only)

Outcome: Change in BMI-SDS Follow-up: 4 and 8 years Overall result: Significant effect of intervention on BMI-SDS at 4 years. At 8 years, no significant effect, except when stratified by SEP SEP results: At 4 years, incident overweight less in high SEP intervention group. At 8 years, intervention effective in high SEP but not low/middle SEP students

Outcome: Change in BMI-SDS, fat mass %, Follow-up: Adjusted follow-up 1.3years. Overall result: Significant increase in fat mass % seen in non-intervention group SEP results: No changes in low-SEP group. High SEP group reduced BMI-SDS compared with normal weight group.

Outcomes

Setting: One of 12 community health centres USA Mexico border Year: 2006–2008;

Setting: Public schools and local community USA Year: 2004–2007

Setting: French National campaign Year: 2001–2005

Setting: Primary schools in Germany Year: 1996 to 2004

Setting: A substudy of KOPS Obesity Prevention Study (Germany) Year: 1996

Context

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Sampling and inclusion

Participants

Jouret et al. (28) Design: RCT Aim: To test strategies for reducing overweight in kindergarten

Epstein et al. (37) Design: RCT Aim: To assess effects of reducing TV and computer use on children’s BMI

Sanigorski et al. (40) Design: quasi-experimental Aim: To evaluate community interventions for childhood obesity

Simon et al. (38) Design: RCT Aim: To assess a physical activity intervention in adolescents.

Recruitment: Kindergartens from one region (n = 156) randomly contacted Inclusion: Parental consent Sample: 3,736 eligible, 1,663 did both baseline and follow-up (44.5% of eligible). No SEP differences in attrition

Recruitment: Newspaper, flyers, and direct mail-outs Inclusion: Aged 4–7 year ≥75th BMI percentile, ≥14 h of TV weekly Sample: baseline n = 70 families; follow-up = 96% Attrition not reported by SEP.

Recruitment: All children in Colac; recruitment not described Inclusion: All preschools and primary schools in Colac with ≥20 students Sample: Baseline = 2,284 (44%–58%) follow-up = 1,807 (83%). Attrition not reported by SEP.

Recruitment: eight randomly selected schools Inclusion: First-level student (6th grader). Sample: Baseline n = 954 (91% of eligible); follow-up = 732 (69.8%). No SEP differences in attrition

Interventions showing an effect in lower SEP groups Schuit et al. (41) Design: Cohort Recruitment: Invited sample Aim: To assess Inclusion: Not reported Sample: effect of CVD Baseline = 4,059 eligible, 3,000 prevention participated (73.9%). Follow-up = 2,414 programme ( (59%). Attrition not reported by SEP.

Study design/aim

Table 2 Continued

Sex: Male: 47%–52% Age: 3.7–3.9 years Anthropometrics: overweight (BMI 85th percentile, 44% obese (BMI > 95th percentile) SEP: parent occupation and education level

Sex: 50.2–53.6% female Age: mean (SD) 8.2 (2.3) to 8.3 (2.2) years Anthropometrics: Intervention group = 18.8% overweight, 8.5% obese; comparison group = 19.7% overweight, 6.8% obese (defined according to the International Obesity Task Force gender – age cut-offs). SEP: Parent education level; area; household income

Sex: 47% male Age: 12years ±0.6 years Anthropometrics: intervention group =23.0% overweight, control group = 23.4% overweight (defined according to the International Obesity Task Force gender – age cut-offs). SEP: parent’s occupation

Sex: Not reported Age 51–52 years Anthropometrics: Mean (SD) BMI: 25.5 (4.1) to 26.3 (3.3) SEP: Indicator not reported

Baseline characteristics

Description: Education and posters in kindergartens, delivered by dietician, general practitioner (GP) followed up ‘at risk’ children Duration: 10 sessions over 2 years.

Description: TV allowance device at home plus financial (up to $2 per week) and other incentives Duration: 2 years

Description: Social marketing policies Community-based activities for behaviour change. Duration: 2–3 years

Description: Multilevel programme; increased PA opportunities delivered by physical educators; local community support Duration: Ongoing

Description: Community-wide n = 554 diet and activity strategies. Partners were city council, community and healthcare committees Duration: 5 years

Intervention

Randomization: N/A Control intervention: None

Randomization: N/A Control intervention: Free access to TV and $2 per week. Parents sent activities per recipes

Randomization: Intervention = town; control group = random sample of nearby region Control intervention: Background activities (not specified)

Randomization: Stratified by sociogeographical criteria Control intervention: None

Randomization: Allocated by region Control intervention: None

Comparison group

Outcome: Change in BMI z-score Follow-up: End of intervention Overall result: Decrease in obesity prevalence SEP results: BMI z-score lower in intervention compared with controls in low SEP, NS in high SEP

Outcome: Changes in BMI z-score Follow-up: End of intervention Overall result: Intervention group showed greater reductions in BMI z-score compared with controls SEP results: Intervention more effective in low-SEP families

Outcome: BMI z-score, waist circumference Follow-up: End of intervention Overall result: Intervention group gained less weight than comparison group SEP results: Intervention effect did not differ by SEP

Outcome: Change in age and gender-adjusted BMI Follow-up: 4 years Overall result: Intervention group showed less adjusted BMI increase than controls SEP results: No interaction effect between intervention and SEP

Outcome: Change in risk factors Follow-up: End of intervention Overall result: Greater reduction in BMI in intervention compared with reference group SEP results: Similar intervention effect in low and high SEP

Outcomes

Setting: Kindergartens in France Year: Not reported

Setting: Homes in the USA Year: Not specified

Setting: Schools and community in Australia Year: 2003–2006

Setting: Schools and community in France Year: 2002–2006

Setting: The Netherlands Year: 1998–2005

Context

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Recruitment: Convenience from five schools Inclusion: Student at participating school Sample: All children in four intervention and one control school (n = 3,769); Subgroup analysis on low-SEP children. Attrition not reported by SEP.

Sampling and inclusion

Participants

© 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

Recruitment: Through e-mail, intranet, or company magazines Inclusion: Working ≥12 h a week, able to understand Dutch Sample: Employees from six organizations; baseline n = 924 (7.2% of eligible); follow-up = 60%. No SEP differences in attrition

Recruitment: All children in two classes at each randomly selected school Inclusion: Children aged 7–9 years Class size ≥15, attending primary school in selected school district Sample: Baseline = 1 582 (97%); follow-up = 1,014 (94%). Higher SEP children more likely to continue in study than lower SEP (P < .001)

Sex: Female: = 49–54% Age: Aged 50 + = 31% intervention; 27% non-intervention Anthropometrics: Obesity 9% both groups SEP: Education level

Sex: 50% female Age: 8 years Anthropometrics: Overweight = 69.7%, obesity =14.3% (defined according to the International Obesity Task Force gender – age cut-offs) SEP: Parental occupation and education level

Sex: 19% men – results stratified by men, plus high-income and low-income women Age: 31–35 years Ethnicity: White = 76–94% Anthropometrics: BMI 26–28 SEP: Family income

Sex: 51% female Age Mean 8 years (range 4–13) Anthropometrics: Baseline measures not reported SEP: Eligible for free school meals.

Baseline characteristics

Description: Web-based intervention. Computer-tailored advice and feedback on PA and dietary intake; Could submit questions to health professionals. Monthly e-mail messages Duration: 2 years

Description: In schools, nutrition added to curriculum, healthy eating and activity encouraged, changes to nutritional environment; Food-based guides for general population; Annual mass media campaigns Duration: Implemented in 2001, ongoing programme

Description: Both intervention groups (education only and education plus lottery) received regular newsletter ± entered into monthly lottery. Delivered by health department Duration: 1 year

Description: Nutritious school meals; healthy nutrition and lifestyle curricula; school-based wellness activities Duration: Interventions applied over 2 years

Intervention

Randomization: Random numbers table Comparison intervention: Usual health promotion programme

Randomization: N/A Comparison intervention: None

Randomization: N/A Comparison intervention: None

Randomization: Done by school district administration Control intervention: None

Comparison group

Outcome: (Secondary) obesity Follow-up: 2 years Overall result: No differences seen on outcomes. Prevalence of obesity stayed at 9% for both intervention and non-intervention group SEP results: No significant differences in intervention effects in low or higher SEP groups

Outcome: Prevalence of overweight/obesity Follow-up: N/A Overall result: Prevalence of overweight/obesity in did not change SEP results: NS decrease in overweight prevalence in each SEP category

Outcome: Change in body weight Follow-up: End of intervention Overall result: No intervention effect SEP results: Low-income women did not respond to intervention. Weight gain in lb (mean, SE); Low-income women control group = 1.30(0.7); Education only = 2.1(1.0);Education + lottery = 3.2 (1.0) (NS)

Outcome: Change in BMI percentile Follow-up: End of intervention Overall result: Significant improvements in intervention group SEP results: Subgroup analysis – effective in low-income children (results not reported in high-income children)

Outcomes

Setting: Worksites in The Netherlands Year: 2007–2008

Setting: Primary schools in France and broader community Year: 2001 – ongoing

Setting: Home-based in the US Year: 1995–1996

Setting: Five elementary schools in Central Florida Year: 2004–2005

Context

BMI, body mass index; BMI-SDS, BMI-standard deviation score; CVD, cardiovascular disease; IQR, interquartile range; KOPS, Kiel obesity prevention study; NNP, national nutrition programme; NS, not significant; PA, physical activity; RCT, randomized controlled trial; SE, standard error; SEM, standard error mean SD, standard deviation; SEP, socioeconomic position; z-BMI, age and sex-standardized BMI.

Robroek et al. (31) Design: Cluster RCT Aim: To evaluate a workplace health promotion programme on nutrition

Salanave et al. (30) Design: Repeat cross-sectional Aim: To monitor changes in obesity in children since the NNP commenced

Interventions showing no overall effect Jeffery et al. (32) Design: RCT Recruitment: Direct phone and Aim: to describe mail-outs, newspapers. Low SES whether weight women targeted gain with age Inclusion: Age 20–45 year, not recently can be pregnant, no serious medical disorder. prevented using Sample: 228 men; 998 women at low intensity baseline; follow-up = 86%. intervention. Lower-income women significantly less likely to continue compared with higher-income women (P < 0.03)

Hollar et al. (36) Design: Quasi-experimental pilot Aim: To examine an intervention to keep children at a healthy weight

Study design/aim

Table 2 Continued

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activity, and prevention of diabetes and cardiovascular disease, with some also including phone follow-up and home visits. At the end of the programme, there was an 18% (95% confidence interval [CI]: 14.9 to 21.1%) weight reduction among all participants, which increased to 28% (95% CI: 23.3 to 30.7%) at 6 months. There were no significant differences by income or education in the percentage of participants achieving successful weight outcomes at programme end or at 6 months. However, in logistic regression analyses, higher-income participants were more likely to achieve weight reduction compared with lower-income participants (odds ratio [OR] at programme end 9.21, 95% CI: 2.50 to 33.99). At 6 months, this difference had disappeared. We rated this study as being of weak quality because of possible selection bias and a high rate of attrition (50% at 6 months and 67% retention at final follow-up). A family-based intervention to prevent weight gain in overweight children was conducted as a substudy of the larger Kiel Obesity Prevention Study (27). The intervention comprised individually tailored, home-based sessions, incorporating education on the development of childhood obesity, influences on children’s eating patterns and the role of physical activity. The intervention was found to be effective overall, whereby intervention children gained significantly less fat mass than non-intervention children (median [interquartile range; (IQR) change in fat mass % = −2.8 (24.4) in intervention children vs. 17.0 (33.4) in nonintervention children, P < 0.05). For BMI-SDS, there were no overall differences between intervention and nonintervention children; however, when results were stratified by SEP, a significant difference in BMI-SDS outcome was seen between lower and higher SEP groups (high SEP intervention group change in median (IQR) BMI-SDS = −0.3 (0.5) compared with low-SEP intervention group, change in median (IQR) BMI-SDS = −0.02 (0.4); P for difference in effect between high and low SEP = < 0.05). The quality of this study was weak because of selection bias (21 of 132 eligible families participated) and no description of potential confounders. In a German trial (33,34), first graders attended schoolbased nutrition education sessions in which messages on diet, physical activity and television (TV) watching were communicated as fairy tales, interactive games and by healthy meals. After each unit, running games were offered. Parents were informed by school meetings and teachers were trained in nutrition education. Overall, findings at both 4 and 8 years were a greater increase in BMI-SDS in the non-intervention compared with the intervention group, although these changes were only significant at 4 years (change in median (IQR) BMI-SDS in nonintervention children 0.15 (−0.28 to 0.61) vs. 0.07 (−0.42 to 0.57) in the intervention group). At both 4 and 8 years follow-up, the intervention was effective in higher but not

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lower SEP children (at 4 years OR for prevalence of overweight in intervention group compared with nonintervention group = 0.35, 95% CI 0.14 to 0.91 for high SEP; OR 1.31, 95% CI 0.69 to 2.46 in low SEP; at 8 years, BMI-SDS = −0.17 and 0.17 in intervention and nonintervention high SEP students respectively, P < 0.001). The quality of this study was classified as weak mainly because of the low rate of participants completing the follow-up (35% at 4 years, 24% at 8 years). A community-based study from the USA (‘Healthy Living Cambridge Kids’) (35) aimed to develop healthy weight interventions for children through ongoing engagement with community members. At the city and community level, interventions included local council endorsement of healthy lifestyle guidelines and raised community awareness of healthy eating and active living opportunities. School-wide interventions included physical activity programmes, new cafeteria menus, school garden programmes and vending machine restrictions. At the family level, tailored strategies were designed to provide skills for addressing health risks. After 3 years of intervention, there was a significant decrease in mean unadjusted BMI z-score for the overall sample (mean BMI z-score change −0.04, P < 0.001), with an effect among high-income but not low-income children (mean BMI z-score change −0.05, P < 0.001 for high-income groups; mean BMI z-score change −0.03 [non-significant] for low-income groups). The prevalence of obesity also decreased significantly, particularly among higher SEP children (−2.1%, P < 0.05). This study was given a ‘weak’ quality rating because of a high attrition rate (52% completed) and potential for selection bias (recruitment strategy was not reported). In France, an ongoing national nutrition programme included nutrition guidelines for the general population, mass media campaigns and obesity screening tools for healthcare professionals (39). The authors used linear regression slopes to examine the evolution of obesity prevalence among adults before (1995–2001) and after (2001– 2005) implementation of the programme. By 2005, the rapid increases in obesity prevalence regression slopes that were previously seen in all occupational grades had slowed among higher grades, but among manual workers obesity prevalence continued to increase. Among men, manual workers had a significantly higher regression slope from 1995 to 2005 compared with other SEP categories (P < 0.001 for difference between manual workers and management/office personnel, and P = 0.02 for difference between manual workers and intermediate white collar workers). Among women, manual workers had significantly higher regression slopes compared with management professionals and intermediate white collar workers (P < 0.001 for both categories). The quality of this study was rated as moderate. © 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

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Studies reporting a beneficial effect among lower socioeconomic position participants We identified six interventions as showing a beneficial effect among lower SEP groups. Three of these studies showed no differential effect by SEP (that is, the intervention was similarly effective among both lower and higher SEP participants). The first of these evaluated a comprehensive physical activity programme for adolescents in France (38). The programme ran over four school years, and included education and opportunities for physical activity at school in a non-competitive environment, regular meetings with parents and teachers to support adolescents’ behaviour and an annual gathering for intervention students. Sporting events and ‘cycling to school’ days were also organized. Local communities provided low-cost entry and transport to pools and sporting facilities and local media was used to reinforce engagement. At 2 and 3 years post-programme, intervention students showed less increase in age and gender-adjusted BMI compared with controls. The differences between intervention and control groups for age and gender-adjusted BMI (95% CI) were −0.26 (−0.43 to −0.08) kg m−2 at 2 years, −0.29 (−0.51 to −0.07) kg m−2 at 3 years and −0.25 kg m−2 (−0.51 to 0.01) at 4 years; the latter of borderline significance only. The interaction effect between the intervention arm and SEP was reported at 4 years only with no significant effect of the intervention by SEP observed, although the small sample size (n = 954) may mean the study was insufficiently powered to detect an interaction effect. A 3-year intervention delivered to all children in one community in regional Australia (40) included school policies on water and fruit breaks, canteen menu changes and promotional materials. Physical activity strategies included after-school activities and walking school buses. At the community level, food outlets used healthier oils for deep frying, festivals were sponsored and there was broad media coverage. At programme completion, overall results showed that children in the intervention community gained less weight than the comparison group (difference in BMI z-score −0.11; 95% CI −0.21 to −0.01). In regression analyses, no differential effect was seen by any indicator of SEP among intervention students, whereas in the comparison population, lower SEP was significantly associated with greater weight gain. This study was given a moderate quality rating. A community-based study investigated the effect of a cardiovascular disease prevention programme in adults, with a total of 193 dietary and 361 physical activity interventions implemented (41). Examples included computertailored nutrition education, supermarket tours, TV programmes, food labelling, walking and cycling clubs, newspaper articles and pamphlet distribution. Partners were municipal councils, general practitioners and local © 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

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communities, and a public–private collaboration with the retail sector. Almost 50% of the interventions took place in low-income areas. After 5 years, there was a smaller increase in BMI in the intervention compared with the reference group (adjusted difference in BMI between intervention and reference groups for men −0.36 kg m−2, standard error [SE] 0.09 (P < 0.05), and among women −0.25 kg m−2, SE 0.10 [not significant]). In regression analysis, adjusted differences in BMI were similar across all SEP groups. The quality of this study was rated as moderate. A study from the USA aimed to assess the effects of reducing TV viewing and computer use on children’s age and sex-standardized BMI (z-BMI) by using a device to limit screen time according to agreed weekly budgets (37). Participants earned up to $2.00 per week for each half hour under budget and the intervention was supported through star charts, home visits, newsletters and parental praise for reducing TV viewing. Control children were given free access to TV and $2.00 per week, while parents received newsletters on parenting tips and child-appropriate activities and recipes. Findings were a decreasing trend in mean z-BMI for both intervention and control groups, with a significantly greater decrease in the intervention group at 12 months (P = 0.03), but not at 24 months. For the lowSEP group, statistically significant between-group differences were seen from baseline to 12 months (P = 0.02) and 18 months (P = 0.04), but not at 24 months (P = 0.05), while no differences were seen for the high SEP group. The quality of this study was rated as high. An RCT tested two strategies for reducing overweight in kindergarten children in France (28). The first strategy (intervention one) consisted of staff education and posters in each kindergarten, plus GP follow-up for ‘at risk’ children. Intervention two used the same strategy, plus extra learning activities about nutrition and activity. Children also received an audio cassette and a story book to reinforce educational messages and parents were provided with information on healthy lifestyle. For kindergartens not in underprivileged areas (higher SEP), there were no differences in overweight following either intervention. However, children from kindergartens in underprivileged areas (low SEP) showed a decrease in median BMI z-score compared with the control group (intervention one, median BMI z-score −0.48 at baseline, −0.14 at follow-up vs. control −0.26 at baseline, 0.71 at follow-up, P = < 0.0001). The quality of this study was rated as high. A significant intervention effect on the prevalence of overweight was also seen in low-SEP kindergartens only. A study was conducted among all students in five elementary schools in Florida (42), with a subgroup analysis undertaken for low-SEP children. Interventions included the provision of nutritious school meals, fruit and vegetable gardens and increased opportunities for

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activity such as a daily desk-side physical activity programme and structured activities during recess. Curriculum-based interventions included provision of educational resources on healthy lifestyle. At study completion, the intervention group had significantly improved their mean BMI percentile compared with the control group (mean change in BMI percentile −1.73, standard deviation 13.6 and −0.47, standard deviation 12.1 in the intervention and control groups respectively). A subgroup analysis found that low-SEP intervention children were more likely to reduce their BMI z-score compared with low-SEP children from control schools; however, data were not presented to allow direct comparison of the intervention effect between higher and lower SEP students so it is not possible to say whether the intervention was equally or more effective in lower SEP participants. This study was identified as being of weak quality because both the proportion of the original sample who completed the study and control of potential confounders were not clearly described.

Common characteristics of interventions Of the five interventions that demonstrated no beneficial effect among lower SEP groups, there were no common characteristics by reach, with settings and target groups varying widely. Intervention duration also varied, with

three of the interventions being very short-term (2–10 weeks). Four interventions were based on the delivery of information only, with few apparent community-level structural or environmental changes to support behavioural modification. The remaining intervention (35) differed from the above studies by involving community and school support for behaviour change through nutrition policies and increased opportunity for physical activity. However, this intervention did include a large information delivery component, based on increasing awareness of healthy guidelines, nutrition and physical education. Of the six studies showing a beneficial effect among lower SEP participants, five had a wide reach, with three being community-based (38,40,41) one conducted in five schools (42) and one across 79 kindergartens (28). The majority of interventions were sustained, ranging from 2 to 5 years. Five of the interventions altered the social or structural environment with the aim of supporting behaviour change; four of these through school or communitywide mobilization (for example, healthy school meals and nutrition policies, or large-scale community-wide interventions) and one by altering the home environment to reduce TV viewing time (37). Conversely, one intervention shown to be effective among lower SEP participants was of short duration, and was based on delivery of information only (28). Overall findings are summarized in Table 3.

Table 3 Results by reach, duration and level of agency* Effect on socioeconomic inequalities

Intervention

Reach (target group/setting)

Duration

Extent to which structural changes were made

No effect in lower SEP groups

Group based exercise/education in community health centre. For adults (32)§ Family counselling for at-risk children (27)§ Education, PA sessions in schools. For children (33,34)§ City-wide policies, community campaigns, vending machine guidelines. For children (35)§ Nutrition guidelines, mass media, obesity screening for adults (39)‡

Individual within group Family Schools Schools and community National

5–24 weeks

Low

10 weeks 2–3 weeks 3 years

Low Low Moderate

Ongoing

Low

Opportunities for PA in supportive environment, free entry and transport to PA facilities. For adolescents (38)† School policies on snacks, menu changes, after-school activities, local community programmes. For children (40)‡ Large number of diet and activity interventions. For adults (41)‡ TV allowance device. For children (37)†

Schools and community Schools and community Community Individual within family Schools Schools

4 years

High

3 years

High

5 years 2 years

Moderate High

2 years 2 years

Low High

Effective in lower SEP groups

Education for children in kindergartens (28)‡ Healthy school meals, education, activities, e.g. fruit and vegetable gardens. For children (42)§ *Excluding studies with no overall effect. † Study methodological quality = strong. ‡ Study methodological quality = moderate. § Study methodological quality = weak. PA, physical activity; SEP, socioeconomic position.

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Effect of findings according to study quality We conducted a sensitivity analysis to explore the impact of study quality on our findings by including strongmoderate quality studies only. This analysis demonstrated similar findings to those seen when all studies were included. Further, the observations regarding level of structural change persisted, whereby those interventions involving greater levels of environmental, social or contextual change were more likely to be effective in lower SEP groups.

Discussion Main findings This is the first review to examine interventions to prevent weight gain according to their effectiveness by SEP. Evidence is limited; we found only 14 studies that evaluated an obesity prevention strategy according to SEP. This is despite the large number of obesity prevention interventions reported in other literature (12,20,21). Similar findings were seen in a Cochrane review of interventions for preventing obesity in children, in which only one of eight included studies had analysed intervention effectiveness by SEP (12). Of the 11 studies we included that showed an effect on anthropometric outcomes, five were not effective among lower SEP participants. The most common characteristic of interventions that were ineffective in lower SEP groups was an emphasis on information delivery. We also found six studies that demonstrated a beneficial effect among lower SEP groups. Attributes of those interventions shown to be effective in lower SEP groups included a wide reach and long duration and a focus on altering environmental or social factors that may act as barriers to healthy behaviours.

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with socioeconomic disadvantage, may limit an individual’s ability to adopt and maintain a healthier lifestyle (19). Conversely, interventions which attempt to address the underlying causes of health inequalities by incorporating some degree of environmental, social or structural change are more likely to be successful across all socioeconomic groups, including the more disadvantaged, because they require fewer individual-level resources to be effective (18,19,43). This theory is supported to some extent by our findings. Among those studies that were not effective among lower SEP groups, one common factor was a dominant focus on information delivery either through the use of mass media campaigns, curriculum-based strategies in schools, counselling or group-based education. In contrast, we found that interventions involving some level of structural or environmental modification were generally more likely to be effective in lower SEP groups. Free access to physical activity facilities or school nutrition policies were effective in all children, regardless of SEP, and in adults a comprehensive community-based programme that included food labelling and the creation of healthy walking clubs was as effective among lower SEP participants as it was among those with higher SEP.

Study quality There is clearly a need for further, methodologically strong, research into the potential effect of strategies on the social gradient in obesity. Of the 11 studies evaluated, we found five studies to be of weak quality. Four of these showed no beneficial intervention effect among lower SEP groups, limiting our conclusions about which intervention characteristics were most likely to contribute to widening inequalities.

Strengths and limitations Why does the effect of interventions differ by socioeconomic position? A growing body of evidence supports the theory that less ‘structural’ interventions (for example, those that focus on information provision rather than attempting to change the context in which a behaviour occurs) are less likely to be effective among lower than higher SEP groups, thereby potentially increasing health inequalities (43,44). These types of interventions have been termed ‘agentic’ (18,43– 45) because they require a high degree of individual agency and/or intent to change behaviour. These interventions may be less successful in lower SEP populations because of fewer resources and less capacity to understand and act upon health messages (18,19). Factors such as low income, poor health literacy, less supportive physical environments or lower levels of self-efficacy, all of which are associated © 2014 The Authors obesity reviews © 2014 International Association for the Study of Obesity

As previously noted, a considerable strength of this review is the comprehensive search of all obesity prevention interventions covering academic (peer-reviewed) and grey literature. However, there are some limitations to note. As with any systematic review, there is potential for publication bias, although this risk was minimized by searching the grey literature. Included papers were in English only and this may have led to the exclusion of studies from non-English speaking countries, thus limiting the generalizability of our findings to other settings and countries. It was unclear whether interventions were sufficiently powered to stratify by SEP as no studies reported power analyses by subgroup. It is therefore possible that there were differential effects by SEP where none were shown, although whether these differential effects would favour lower or higher SEP groups is uncertain. For studies that reported percentiles, if they did not adjust for age and sex

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then these results must be interpreted with caution as they do not take into account normal BMI variation with age.

Implications for policy and research Given the generally weaker quality of interventions that were not effective in lower SEP groups, it is difficult to draw firm conclusions. Despite this, our findings add to the developing theory that information-based interventions risk increasing existing health inequalities. Obesity prevention strategies based solely on information provision are established across many countries and settings. It is essential that where these interventions are already in place, they are evaluated for their socioeconomic impact and where required, are supported by additional strategies targeted towards preventing weight gain among lower SEP groups, in addition to being embedded within broader strategic initiatives (43,44). There is evidence from the tobacco control literature suggesting that supporting broader policies, such as price increases, with targeted measures specifically directed to the disadvantaged (such as smoking cessation services in deprived areas) may effectively reduce or minimize educational inequalities in smoking (46). Further research is required to identify and evaluate appropriate support strategies for obesity prevention (47), although early findings from work being undertaken in the USA are encouraging (48,49). Of note, two protocols for systematic review of the effectiveness of public health interventions to reduce inequalities in obesity have recently been published (13,48). The proposed reviews will include interventions that aim to reduce inequalities in obesity; as such they will include interventions specifically targeting lower socioeconomic groups. We suggest that these reviews will complement our findings by identifying which measures are most likely to prevent weight gain among disadvantaged groups, and so demonstrate potential to support population-level obesity prevention strategies to minimize inequalities. Recent evidence from a systematic review of schoolbased nutrition and physical activity policies for children suggests that single policies implemented in isolation are less likely to be effective at an overall population level than are those policies which are more comprehensive and multifaceted, incorporating broader stakeholder and family engagement (50). Similarly, we found that interventions that were effective in lower SEP groups tend to be those of longer duration that incorporate some environmental, structural, community or social support for behaviour change; for example, improved community access to physical activity or mandatory school nutrition policies. Interventions with these characteristics must be given priority if we are to reduce population levels of obesity without increasing socioeconomic inequalities in population weight. A consideration here is the concept of proportion-

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ate universalism, within which interventions are implemented with a scale and intensity that is proportionate to the level of disadvantage (51). This might mean that where pre-existing socioeconomic gradients in obesity are shown to exist, even the most structural of interventions may require supplementing with strategies shown to be effective in lower SEP groups (43).

Conclusion There is currently very little evaluation of the potential health equity impact of obesity prevention strategies and further evidence is required. Despite this limitation, findings from our review suggest that more structural approaches to obesity prevention are less likely to widen existing inequalities in obesity. If we are to reduce the burden of overweight and obesity among lower socioeconomic groups then all existing and proposed obesity prevention interventions must be measured for their impact on socioeconomic inequalities in health. Those that are more equitable should be prioritized, while those that are not must either not be used, or must be complemented with strategies that will not leave the disadvantaged behind.

Funding This work was supported by an Australian National Preventive Health Agency grant (188PEE2011), an Australian Research Council grant (ARC LP12010041), a National Health and Medical Research Council Career Development Award (to AP) and a National Heart Foundation postdoctoral fellowship (PH 12 M6824 to KB).

Acknowledgements We would like to acknowledge the chief investigators and advisory board for the Australian National Preventive Health Agency and Australian Research Council grants.

Conflict of interest statement No conflict of interest was declared.

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