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Obesity Research & Clinical Practice (2015) xxx, xxx—xxx

ORIGINAL ARTICLE

Obesity in adolescents with intellectual disability: Prevalence and associated characteristics Sharon Krause a, Robert Ware b,c, Lyn McPherson b,∗, Nicholas Lennox b, Michael O’Callaghan d a

Lady Cilento Children’s Hospital, Queensland Children’s Health Services, Child Development, South Brisbane, Qld, Australia b Queensland Centre for Intellectual and Developmental Disability, MRI-UQ, The University of Queensland, South Brisbane, Qld, Australia c School of Population Health, The University of Queensland, Herston, Qld, Australia d Pediatrics and Child Health, The University of Queensland, Herston, Qld, Australia Received 16 December 2014 ; received in revised form 9 October 2015; accepted 11 October 2015

KEYWORDS Intellectual disability; Obesity; Adolescent; Down syndrome; Risk factors

Summary Objective: Studies from a number of countries have indicated an increased risk of obesity in adolescents with intellectual disability. Whether risk factors for adults with intellectual disability apply to adolescents however is uncertain. This study examines obesity in a community sample of adolescents with intellectual disability in Australia, and investigates risk factors associated with obesity and overweight. Methods: A cross-sectional survey and medical record review on 261 adolescents with intellectual disability attending special education facilities in South-East Queensland, Australia between January 2006 and September 2010 was conducted. Information on age, gender, weight, height, syndrome specific diagnoses, problematic behaviours, mobility, taking psychotropic or epileptic medication, and perceived household financial difficulties was collected. Body mass index (BMI) was calculated and participants categorised as normal/underweight, overweight or obese according to the International Obesity Taskforce definitions. Results: Overall 22.5% (95% CI: 17.8—28.0%) of adolescents were obese, and 23.8% (95% CI: 19.0—29.4%) were overweight, a marked increase compared to Australian norms. Adolescents with Down syndrome were more likely to be obese than other participants (odds ratio = 3.21; 95% CI: 1.41—7.30). No association was found with other risk factors examined.



Corresponding author at: Queensland Centre for Intellectual and Developmental Disability, The University of Queensland, Mater Misericordiae Hospital, South Brisbane, Qld 4101, Australia. Tel.: +61 7 3163 8267; fax: +61 7 3163 2445. E-mail address: [email protected] (L. McPherson). http://dx.doi.org/10.1016/j.orcp.2015.10.006 1871-403X/© 2015 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

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S. Krause et al. Conclusions: Prevalence of obesity and overweight were increased compared to general Australian adolescents. The only significant risk factor was the presence of Down syndrome. These findings reinforce the need for a health policy and practice response to obesity that is inclusive of individuals with intellectual disability. © 2015 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

Introduction Obesity has been identified as one of the major public health concerns of the 21st century [1]. One of the most important long-term consequences of childhood and adolescent obesity is its persistence into adulthood [2,3]; 70% of obese adolescents remain obese in adulthood with physiological, psychological and social consequences [4]. While substantial information is available on adolescent obesity in the general population, less is known about obesity in adolescents with intellectual disability (ID). Reviews by Melville et al. [5] and Rimmer and Yamaki [6] indicate that prevalence of obesity amongst adults with ID is higher than general population prevalence. Risk factors associated with obesity in adults with ID include being female, presenting with less severe level of ID (mild—moderate), using psychotropic medication, being physically inactive and living in less restrictive environments. The risk for obesity remains high even in those who are ambulatory. Fewer studies have focused on children and adolescents with ID. Recent reviews by Maiano [7] and Grondhuis and Aman [8] have highlighted that the majority of studies involving adolescents reported an increased prevalence of overweight and obesity. Studies varied in their size, study design and definitions. Findings suggested similar risk factors to adult studies, though the majority of studies focused on prevalence. A 2013 study concluded that literature since the 2011 review had also focused primarily on prevalence, and the risk factors of age and gender [9]. A subsequent five studies [10—14] confirm an increased prevalence of overweight and obesity among adolescents with ID, while the large study from Korea [10] reports obesity increasing with age and female gender. A systematic review of parental factors associated with obesity in children with disability [15] suggested socioeconomic status, parental body mass

index (BMI), level of physical activity and parental perceptions as associated, though firm conclusions could not be drawn because of the limitations of this literature. Grondhuis and Aman [8] have called for action in addressing this important issue of obesity in children and adolescents with ID. People with ID are at greater risk of developing secondary health problems compared to their counterparts without ID. Reasons for this include higher levels of general health problems, specific syndrome-related conditions that contribute to poor health status and a general lack of health screening and promotion targeted to this population [16]. Advocacy and communication skills as well as training of medical practitioners in care of individuals with ID may influence this. The prevalence of obesity is one of a number of commonly used measures of health inequality [17]. In addition, it is likely that the increased prevalence of obesity contributes to other health inequalities people with ID experience, i.e. raised mortality rates and high levels of unmet health needs [18]. The aim of this study was to determine the prevalence of obesity and overweight in a community sample of adolescents with ID and, based on findings in the adult and child/adolescent literature on this topic, to examine specific associations with gender, age, mobility, presence of behaviour problems, use of psychotropic medication, presence of Down syndrome and family financial difficulties.

Methods Study population We investigated a sample of adolescents with ID living in South-East Queensland, Australia between January 2006 and September 2010. The data reported are derived from a randomised controlled trial (Ask study) investigating the effectiveness of

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Obesity in adolescents with intellectual disability a health intervention package in improving longterm health of adolescents with ID [19]. Schools in south-east Queensland were the unit of randomisation, stratified by type and location. The schools involved were those that were special education schools (SES) or attached special education units (SEU) who had students with ID and/or physical disability. In the original Ask study, 85 schools were randomly selected for the study and included 51.3% within a major city and 48.7% from regional areas. Adolescents from both the intervention and control arms of the Ask trial were eligible for inclusion in the current study. This study is a subset of information gathered within the carer baseline survey (2007) and paired general practitioner medical records obtained at completion of the intervention trial (2009—2010). The carer baseline survey included demographic data about the adolescent and the carer, home environment, health knowledge and records, psychological stressors for the carer including financial and behavioural issues surrounding the adolescent. For those carers who requested verbal interview these were conducted by telephone. Complete medical records from general practitioners were obtained where available.

Measures Adolescents with ID attending SES or SEU units must fulfil criteria provided by the State government in relation to access. Verification for the category of ID (used interchangeably with ID and reflecting DSM criteria) is based on significant limitations in intellectual function which also require significant educational adjustments in relation to schooling. Functional impact on activities of daily living is also considered. This requires evidence from a psychologist or school guidance officer of formal neurocognitive testing [20]. Overweight/obesity General practitioner records were extracted via computer printout or manually photocopied. Records were de-identified and numbered. The paired height and weight data was extracted when available and paired with the responses to the baseline survey. Age at time measurement and BMI were calculated. When measurements were recorded on the same individual more than once in the study period, the latest measurements recorded in the GP records were used for this study. The BMI was calculated as weight (in kg) over square of the height (m), i.e. kg/m2 . The BMI was converted to the International Obesity Taskforce (IOTF) percentile values using age- and gender-specific cut-offs equivalent

3 to adult BMI of >25 kg/m2 (for overweight) and >30 kg/m2 (for obesity) [21]. Clinical, social and behavioural characteristics Clinical, social and behavioural characteristics of the participants were reported by their parents/carers at baseline. Behaviour problems were categorised according to the Developmental Behaviour Checklist-Short Form DBC-P24, a 24item version of the DBC-P (parents/carers version), which provides an overall measure of psychopathology in young people with ID [22,23]. A Mean Behaviour Problem Score of 0.48 was used as a cut-off for presence of significant problematic behaviours [23] and a cut-off of 0.75 was used to identify major behaviour problems [24]. Adolescents mobility was categorised as either completely independent, walks with aid, uses wheelchair, or immobile. Psychotropic medication was classified according to The World Health Anatomical Therapeutic Chemicals (ATC) classification [25]. Carers reported whether they perceived their household was in financial difficulties [26]. Diagnosis of Down syndrome This was by carer report in the baseline survey. Medication use This was based on information completed by the intervention carers and medical records review. Psychotropic medication was classified according to The World Health Anatomical Therapeutic Chemicals (ATC) classification [25].

Statistical analysis Data is summarised as mean (standard deviation) for continuous variables and frequency (percentage) for categorical variables. The weighted prevalence and 95% confidence intervals (95% CIs) of overweight/obese was calculated. Due to the higher rate of weight recording for adolescents with Down syndrome, calculations were weighted by presence/absence of Down syndrome to reflect the proportion of adolescents with Down syndrome in the full intervention study sample. The association between demographic and clinical characteristics and overweight/obese was examined using weighted logistic regression, first univariably and then multivariably. All multivariable models were adjusted for sex, age, Down syndrome, behaviour problems, mobility, financial difficulties, and use of psychotropic medication. Possible interaction effects between demographic and clinical characteristics and overweight/obese

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were investigated using weighted logistic regression. Results are reported as odds ratios and 95% confidence intervals. All analyses were conducted using Stata statistical software v 12.0 (StataCorp, College Station, TX, USA).

Ethical approval Prior ethics approval for the original trial of the health intervention package, of which this is a sub-study, was granted by both the University of Queensland Behavioural and Social Sciences Ethical Review Committee (Clearance No: 2004000081) and the Queensland Government Department of Education and the Arts (File No: 550/27/424).

Results Completed carer questionnaires were obtained for 593 adolescents and completed general practitioner records were obtained for 436 of these participants. Mean age, gender and SES quintile were compared for these 436 adolescents to all students attending special schools or special education programmes in south-east Queensland. Though the data did not allow a direct statistical comparison, the Ask study group appeared very similar in SES quintile distribution and age, though the proportion of males appeared lower (61% overall vs 55% in Ask study). Of the 436 adolescents, 261 in the 13—18 year range had recorded weights and heights that enabled calculation of the BMI. Characteristics of participants are reported in Table 1. Of the 261, 145 (55.6%) were boys, 42 (16.1%) had Down syndrome, 109 (42.4%) had major behavioural problems and 47 (18.1%) had epilepsy. Ask study adolescents who had BMI data recorded were generally similar to the 332 adolescents where BMI was not recorded, although adolescents with Down syndrome were slightly more likely to have BMI recorded (55.2% had BMI recorded) than others (42.4%). There were no statistically significant differences in characteristics according to whether BMI was recorded (Table 1). The overall prevalence of obesity for all adolescents with ID in this study was 22.5% (95% CI: 17.8—28.0%) and overweight 23.8% (95% CI: 19.0—29.4%). Amongst males, the prevalence for obesity and overweight were 22.0% (95% CI: 16.0—29.5%) and 21.4% (95% CI: 15.4—28.9%) respectively, compared with prevalences of 23.1% (95% CI: 16.3—31.7%) and 26.7% (95% CI 19.5—35.5%) in females. The prevalence for

obesity and overweight in adolescents with Down syndrome were 35.7% (95% CI: 22.7—51.2%) and 33.3% (95% CI: 20.8—48.8%), compared to 20.6% (95% CI: 15.7—26.5%) and 22.4% (17.3—28.4%) in those without. Table 2 displays the association between demographic and clinical characteristics and BMI categories. Females were slightly more likely to be obese (unadjusted OR = 1.19 (95% CI 0.64, 2.20) and overweight (1.41; 95% CI 0.77, 2.58)) than males. Presence of Down syndrome was associated with an increased risk of both being obese (unadjusted OR = 3.21 (95% CI 1.41, 7.30) and overweight = 2.75 (95% CI 1.20, 6.30)). After adjusting for potentially confounding variables the adjusted OR for obesity = 2.61 (95% CI 1.04, 6.55). Similarly for overweight the adjusted OR was 2.36 (95% CI 1.01, 5.56), and for overweight and obesity combined, the adjusted OR = 2.46 (95% CI 1.16, 5.19). The relationships between age, behaviour problems, mobility, psychotropic medication (with or without the inclusion of anti-epileptics) and family financial difficulties with BMI categories were neither strong nor statistically significant. Similarly, no significant interaction effects were present. Two additional analyses were performed to further examine the increased prevalence of obesity in adolescents with Down syndrome (Supplementary Tables 1 and 2). After stratification by Down syndrome there was little association between age and overweight/obesity in those without DS, but participants with DS were less likely to be overweight/obese if aged 16—18 years compared with age 13—15 years (adjusted OR = 0.08; 95% CI = 0.01, 0.66). Due to the small number of participants with DS aged 13—15 of normal weight (2/15, 13.3%) this estimate should be treated cautiously.

Discussion This study reports a high prevalence of obesity and overweight in adolescents with ID. The prevalence for obesity in this study of 22.0% in males and 23.1% in females is substantially higher than that reported in a large 2010 survey of Australian students using the IOFT classification where for year 10 (15—16 years) male obesity was 7.6% and female obesity was 3.4% with overall obesity prevalence of 5.6% [27]. Prevalence of overweight in the Ask study was 21.4% in males and 26.7% in females compared to 17.1% and 15.7% in the schools study. Down syndrome was significantly associated with higher risk

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Obesity in adolescents with intellectual disability Table 1

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Baseline characteristics of participants in the Ask study, according to whether BMI was recorded. BMI recorded 261 15.4 (1.5) 145 (55.6)

BMI not recorded 332 15.6 (1.8) 179 (53.9)

P-value

Total number of participants Age (years) — mean (SD) Male — gender Cause of disability Down syndrome Other known cause Unknown

42 (16.1) 144 (55.2) 75 (28.7)

34 (10.2) 189 (56.9) 109 (32.8)

0.15

34 (13.1) 59 (22.7) 66 (25.4) 56 (21.5) 45 (17.3)

32 (9.7) 77 (23.3) 80 (24.2) 78 (23.6) 63 (19.1)

173 (52.1) 159 (47.9)

147 (56.3) 114 (43.7)

62 (23.8) 99 (37.9) 75 (28.7) 22 (8.4) 3 (1.1)

104 (31.3) 92 (27.7) 102 (30.7) 30 (9.0) 4 (1.2)

0.09

Physical mobility Completely independent Walk with aid Uses wheelchair Immobile

229 (87.7) 22 (8.4) 8 (3.1) 2 (0.8)

281 (85.2) 21 (6.4) 24 (7.3) 4 (1.2)

0.10

Communication Mainly/entirely verbal Some verbal with nonverbal aids Mainly nonverbal Mainly facilitated

192 (73.8) 41 (18.8) 18 (6.9) 9 (3.5)

259 (78.7) 37 (11.2) 25 (7.6) 8 (2.4)

0.34

Behaviour problems No Minor Major

77 (30.0) 71 (27.6) 109 (42.4)

111 (33.6) 83 (25.2) 136 (41.2)

0.61

Health conditions Epilepsy Heart condition Psychiatric condition Diabetes Vision problem Hearing problem Thyroid problem Constipation Reflux oesophagitis Aspiration

47 (18.1) 35 (13.5) 23 (9.1) 2 (0.8) 90 (34.7) 36 (13.8) 12 (4.6) 36 (13.8) 18 (6.9) 6 (2.3)

74 (22.5) 29 (8.8) 16 (4.9) 3 (0.9) 97 (29.6) 46 (13.9) 9 (2.7) 50 (15.2) 16 (4.8) 7 (2.1)

0.19 0.07 0.05 0.85 0.18 0.97 0.22 0.66 0.28 0.88

Anti-psychotic medication

75 (30.2)

51 (27.1)

0.48

Socio-economic quintile Lowest Lower Middle Higher Highest School type Special education unit Special education school General health Excellent Very good Good Fair Poor

0.10 0.74

0.72

0.32

Note: Values are percentage (frequency) unless otherwise stated. Missing items when BMI recorded: communication, n = 1; behaviour problems, n = 4; medication, n = 13. When BMI not recorded: mobility, n = 2; communication, n = 3; behaviour problems, n = 2; medication, n = 144. Health conditions recorded as ‘‘Don’t Know’’ when BMI recorded: epilepsy, n = 1; heart condition, n = 1; psychiatric condition, n = 5; diabetes, n = 2; vision problem, n = 2; hearing problem, n = 1; thyroid problem, n = 2; constipation, n = 1; reflux oesophagitis, n = 2; aspiration n = 1. When BMI not recorded: epilepsy, n = 3; heart condition, n = 1; psychiatric condition, n = 8; diabetes, n = 3; vision problem, n = 4; hearing problem, n = 2; thyroid problem, n = 4; constipation, n = 2; reflux oesophagitis, n = 2; aspiration n = 3.

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Over-weight, n

Over-weight; prevalence (95% CI)

Obese; n

Obese; prevalence (95% CI)

Normal vs over-weight; crude; OR (95% CI)

Sex Male Female

145 116

31 32

21.4% (15.4%, 28.9%) 26.7% (19.5%, 35.5%)

33 27

22.0% (16.0%, 29.5%) 23.1% (16.3%, 31.7%)

1.00 1.41 (0.77, 2.58)

Age 13—15 16—18

119 142

26 37

21.5% (15.0%, 29.8%) 25.7% (19.2%, 33.6%)

32 28

26.1% (19.0%, 34.7%) 19.4% (13.7%, 26.8%)

1.00 1.14 (0.62, 2.10)

Down syndrome No Yes

219 42

49 14

22.4% (17.3%, 28.4%) 33.3% (20.8%, 48.8%)

45 15

20.6% (15.7%, 26.5%) 35.7% (22.7%, 51.2%)

1.00 2.75 (1.20, 6.30)

Behaviour problems None Minor Major

81 71 109

22 18 23

27.4% (18.6%, 38.4%) 25.1% (16.3%, 36.5%) 21.3% (14.5%, 30.1%)

13 19 27

16.3% (9.6%, 26.3%) 26.6% (17.6%, 38.1%) 24.2% (17.0%, 33.1%)

1.00 1.07 (0.49, 2.32) 0.80 (0.39, 1.64)

Mobility Independent Not independent

229 32

55 8

23.5% (18.5%, 29.5%) 25.6% (13.3%, 43.5%)

54 6

23.2% (18.1%, 29.1%) 17.7% (8.0%, 34.5%)

1.00 1.02 (0.42, 2.51)

Financial difficulties No Yes

135 123

33 29

23.8% (17.4%, 317%) 23.6% (16.9%, 32.0%)

31 28

22.6% (16.3%, 30.5%) 22.2% (15.7%, 30.4%)

1.00 0.98 (0.54, 1.80)

Psychotropic medication No Yes

176 72

42 20

23.3% (17.6%, 30.1%) 27.8% (18.6%, 39.3%)

44 15

24.6% (18.8%, 31.6%) 20.5% (12.6%, 31.3%)

1.00 1.20 (0.62, 2.33)

Psychotropic medication + anti-epileptic No 162 39 Yes 86 23

23.4% (17.5%, 30.6%) 26.8% (18.5%, 37.3%)

43 16

26.2% (19.9%, 33.5%) 18.3% (11.5%, 28.0%)

1.00 1.05 (0.56, 1.99)

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Table 2 Association between demographic and clinical characteristics and overweight and obesity. Logistic regression results presented as odds ratio (95% confidence interval). Prevalence and regression results are weighted by presence of Down syndrome. Adjusted analyses include sex, age, Down syndrome, behaviour problems, mobility, financial difficulties, and use of psychotropic medication as covariables.

Normal vs obese; crude; OR (95% CI)

Normal vs obese; adjusted;OR (95% CI)

Normal vs over-weight/obese; crude; OR (95% CI)

Normal vs over-weight/obese; adjusted; OR (95% CI)

Sex Male Female

1.00 1.55 (0.82, 2.93)

1.00 1.19 (0.64, 2.20)

1.00 1.23 (0.64, 2.38)

1.00 1.30 (0.79, 2.13)

1.00 1.38 (0.81, 2.35)

Age 13—15 16—18

1.00 0.87 (0.45, 1.68)

1.00 0.71 (0.38, 1.32)

1.00 0.62 (0.32, 1.21)

1.00 0.91 (0.55, 1.48)

1.00 0.74 (0.43, 1.27)

Down syndrome No Yes

1.00 2.36 (1.01, 5.56)

1.00 3.21 (1.41, 7.30)

1.00 2.61 (1.04, 6.55)

1.00 2.97 (1.46, 6.04)

1.00 2.46 (1.16, 5.19)

Behaviour problems None Minor Major

1.00 0.87 (0.38, 1.96) 0.59 (0.25, 1.36)

1.00 1.90 (0.81, 4.44) 1.53 (0.70, 3.34)

1.00 1.82 (0.74, 4.47) 1.43 (0.56, 3.65)

1.00 1.38 (0.72, 2.65) 1.07 (0.59, 1.94)

1.00 1.20 (0.60, 2.40) 0.87 (0.43, 1.78)

Mobility Independent Not independent

1.00 0.95 (0.37, 2.43)

1.00 0.72 (0.27, 1.93)

1.00 0.72 (0.25, 2.03)

1.00 0.87 (0.41, 1.84)

1.00 0.84 (0.37, 1.90)

Financial difficulties No Yes

1.00 1.08 (0.56, 2.11)

1.00 0.97 (0.52, 1.80)

1.00 0.96 (0.49, 1.90)

1.00 0.98 (0.60, 1.60)

1.00 1.02 (0.59, 1.77)

Psychotropic medication No 1.00 Yes 1.63 (0.78, 3.42)

1.00 0.84 (0.41, 1.70)

1.00 0.99 (0.44, 2.21)

1.00 1.01 (0.58, 1.77)

1.00 1.29 (0.70, 2.38)

Psychotropic medication + anti-epileptic No 1.00 Yes 1.34 (0.66, 2.71)

1.00 0.64 (0.32, 1.28)

1.00 0.71 (0.33, 1.52)

1.00 0.84 (0.49, 1.42)

1.00 0.99 (0.55, 1.78)

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Normal vs over-weight; adjusted;OR (95% CI)

Characteristic

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Table 2

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of obesity and overweight compared to other study youth with ID. BMI category was not associated with gender, age, level of mobility, medication use or parent/carer self-reported financial difficulties. A 2014 Lancet review compared normal population data on prevalence of overweight and obesity in children and adolescents from 183 countries. Substantial differences existed, with prevalence higher in developed compared to developing countries [28]. Though similar information is not available for adolescents with ID, a range of studies from different countries have however reported an increased prevalence of overweight and obesity among adolescents with ID. This reported prevalence however will be relative to the normal population data of individual countries. Studies also differ in selection processes, inclusion and exclusion criteria such as including youth with syndromes or physical impairment, study numbers, year the study was undertaken, gender, age range, and criteria for defining categories of overweight and obesity. Lower rates of obesity are generally reported in younger children with ID [29]. A combined overweight and obesity prevalence of 32% for youth 15—18 years, 21% for those 11—14 years, and 14% for those 7—10 years was reported for a recent large Korean study with a higher prevalence in girls [10]. In his review of 10 papers Maiano [7] examined publications from seven countries and reported the prevalence rates of obesity using the 95th CDC percentile cut-off suggest ranges from 18 to 36%; whereas the results from the studies relying on the IOTF cut-off adjusted for age and gender report prevalence rates of obesity from 7 to 15.3%. If prevalence from these studies is compared to individual country population prevalence for children and youth less than 20 years described in the Lancet review [28], the overall risk of obesity in children with ID is generally elevated 2—3 fold. A low prevalence of obesity of 7.2% was reported in France [9] and Hong Kong [30] though the latter may be influenced by smaller numbers and exclusion of youth with Down syndrome. A tertiary hospital population in Australia in 2008, showed a similar rate of overweight (24.5%) to our study, however a lower rate of obesity (15.3%) [31]. Obesity prevalence in reports from North America [18] and Scotland [32] were higher than in our report. Three papers [12,33,34] have examined data from participants in the Special Olympics. The 2012 study compared overweight and obesity prevalence in 7643 youth aged 12—18 years according to country of origin, grouped into six global regions. The highest prevalence was in North America and lowest in East Asia, Latin America and Asia Pacific.

In the 2014 study BMI category of participants were grouped by the economic status of the participating country. High income countries had a prevalence of combined overweight and obesity of 42% compared to 28%, 31% and 25% in low, low-middle and middle income countries. BMI categories of Special Olympic participants may not however accurately reflect comparable community prevalence in their country. Though BMI is widely used as a measure of overweight and obesity, especially in larger community studies, Salaun [35] suggests BMI may underestimate actual adipose tissue in individuals with ID compared to bioimpedence measures. Nevertheless, BMI remains the main measure of obesity in larger epidemiological studies. Presence of Down syndrome as a risk factor for overweight and obesity was confirmed in a large national study in the Netherlands [36]. For obesity the prevalence was 4.2% in males and 5.1% in females compared to the normal population prevalence of 1.8% and 2.2% respectively using IOTF criteria. Although well accepted that individuals with Down syndrome are more likely to be obese [37], studies have been inconclusive amongst adolescents with ID regarding the extent to which Down syndrome was an additional independent risk factor [7]. Our findings support Down syndrome being an independent risk factor for overweight and obesity among adolescents with ID. Although in adulthood, women with ID are at greater risk of overweight and obesity [5] this does not appear to be the case amongst adolescents with ID with the majority of studies showing no association with gender [7]. Findings of this study do not support a significant gender effect on prevalence of obesity. The majority of studies have reported that prevalence of overweight and obesity in children and adolescents with ID does not increase from childhood to adolescence [7,9]. Similar to the smaller Australian study [31] we did not find any association between age and increasing prevalence of obesity. Little research has examined the association between mobility levels and obesity in adolescents with ID. In this study, no association was found between obesity and overweight and with varying with level of mobility. A study in Taiwan reported that only 8% of adolescents with ID reached the recommendations for exercise [38]. There was no significant association with prevalence rates and self-reported financial difficulties. A 2013 systematic review [15] suggested that firm

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Obesity in adolescents with intellectual disability conclusions could not be drawn regarding the relationship to socioeconomic status.

Study limitations Factors influencing recruitment of families within schools and incomplete data on BMI within the study sample may have affected estimates of obesity prevalence. Overall the youth included in the Ask study were similar to eligible students not included. Within the Ask study itself, adolescents with BMI measurements were very similar to those without BMI measurement available, except possibly for the over-representation of adolescents with Down syndrome. Measures of association are less susceptible to potential bias than estimates of prevalence. Using weighted logistic regression, the adjusted OR for obesity in youth with Down syndrome compared to participants of normal weight of 2.61 (1.04, 6.54). This supports the study finding of a specific increase in obesity risk of adolescents with Down syndrome. Incomplete height and weight measures by General Practitioners is not uncommon [39] and further highlights the barriers individuals with ID have in adequate health care where incomplete medical records and understanding of health needs of the intellectually disabled population are commonplace [40]. Information on medical diagnosis in the adolescents was based on parent/carer report. It is unlikely that rare syndromes associated with obesity contribute substantially to these findings. We have not examined a range of factors such as birth weight, parental body mass index, level of physical activity, and diet associated with obesity in adolescents with ID.

Conclusions This study reports higher rates of obesity and overweight amongst adolescents with ID, especially adolescents with Down syndrome, although no association with other risk factors identified in adult studies. Factors associated with obesity and overweight in adolescents without ID, such as diet and lifestyle characteristics, as well as factors considered in our current study require further investigation in this population. From a clinical perspective, an important implication is on surveillance and anticipatory guidance, and intervention when indicated, though intervention may be more difficult given the high prevalence of associated behaviour problems. The key issue however is a health policy and practice response at a community

9 and public health level that is inclusive of individuals with ID.

Conflicts of interest The authors have no disclosures or conflict of interest to declare.

Acknowledgements SK conceptualised and designed the study in consultation with the other authors, assisted with the analysis and wrote the first draft of the paper. RW assisted with the conceptualisation and design of the study, analysed and interpreted the data and reviewed the manuscript. NL is chief investigator of the Ask Study and together with LM and MO conceptualised and designed the study in consultation with the other authors, assisted with the interpretation of data and reviewed the manuscript. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work. The authors would also like to acknowledge the contribution of Professors Chris Bain, Suzanne Carrington, and Gail Williams, who were investigators on the randomised controlled trial from which this data was obtained. The trial was financially supported by the Australian National Health and Medical Research Council (Project Grant No. 401647).

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.orcp.2015.10.006.

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Obesity in adolescents with intellectual disability: Prevalence and associated characteristics.

Studies from a number of countries have indicated an increased risk of obesity in adolescents with intellectual disability. Whether risk factors for a...
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