PEDIATRICOBESITY doi:10.1111/ijpo.266
Association between breastfeeding and body mass index at age 6–7 years in an international survey R. J. Hancox1, A. W. Stewart2, I. Braithwaite3,4, R. Beasley3,4, R. Murphy5, E. A. Mitchell6 and ISAAC Phase Three Study Group*
Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, New Zealand; 2School of Population Health, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand; 3 Medical Research Institute of New Zealand, Wellington, New Zealand; 4Capital and Coast District Health Board, Wellington, New Zealand; 5Department of Medicine, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand; 6Department of Paediatrics: Child and Youth Health, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand
Summary
Address for correspondence: Dr RJ Hancox, Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, Dunedin 9053, New Zealand. E-mail: [email protected]
Results: Data were available for 76 635 participants from 31 centres in 18 countries. Reported breastfeeding rates varied from 27 to 98%. After adjusting for potential confounders, the estimated BMI difference was 0.04 kg m−2 lower among those who had been breastfed (P = 0.07). The risk for being overweight or obese was slightly lower among breastfed children (odds ratio = 0.95, P = 0.012). There was no evidence that the association between breastfeeding and BMI was different in lower income countries compared with higher income countries.
1
*Full listing of study group members appear at the end of this manuscript. Received 11 December 2013; revised 4 August 2014; accepted 2 September 2014
Background: Breastfeeding is believed to reduce children’s risk for obesity but data are conflicting. It is also uncertain if breastfeeding has different effects on obesity in high- and low-income countries. Objectives: This study aimed to investigate the association between having been breastfed and body mass index (BMI) in 6- to 7-year-old children in a large international survey. Methods: Parents/guardians reported whether their child had been breastfed and their current height and weight. Some centres measured height and weight directly. Analyses adjusted for whether height and weight were reported or measured, child’s age, sex, country gross national income and centre.
Conclusions: The findings suggest that breastfeeding has little impact on children’s BMI. Increasing breastfeeding is unlikely to reduce the global epidemic of childhood obesity. Keywords: Body mass index, breastfeeding, children, obesity. Abbreviations: BMI, body mass index; ISAAC, International Study of Asthma and Allergies in Childhood.
Introduction There is a widely held belief that breastfeeding children will help to prevent overweight and obesity later in life. Numerous observational studies and meta-analyses of these studies indicate a lower risk of overweight and obesity in those who have been breastfed (1–7), and biologically plausible mechanisms have been proposed to explain this protective effect (8). However, the effect of breastfeeding on risk for obesity remains controversial because the observational associations between breastfeeding and a lower risk for obesity may be subject to confounding by socioeconomic and other environmental factors (7,9–11). Moreover, the data available to systematic reviews and meta-analyses appear to have been influenced by publication bias and selective reporting of favourable findings (12).
© 2014 World Obesity. Pediatric Obesity ••, ••–••
A recent article described the belief that breastfeeding reduces the risk for obesity as a ‘myth’ – defined as a belief that persists despite substantial evidence that it is not true (13). The strongest evidence to support this view comes from the PROBIT study: a large cluster randomizedcontrolled trial promoting breastfeeding to women in Belarus (14,15). The intervention was effective in increasing duration of breastfeeding but did not find any evidence for reduced childhood obesity at ages 6.5 or 11.5 years among those who had been breastfed. A limitation of this study include the fact the PROBIT study recruited mothers who were intending to breastfeed, and thus most infants in the control group were breastfed to some extent. Moreover, the prevalence of obesity in children in Belarus was much lower than in many other countries reducing the power of the study to detect an association between breastfeeding and a lower risk for obesity.
ORIGINALRESEARCH
ORIGINALRESEARCH
ORIGINALRESEARCH
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R. J. Hancox et al.
Most research on the association between breastfeeding and obesity has been performed in high-income rather than low- or middle-income countries. This is important because the confounding effects of the social and cultural determinants of breastfeeding practices and risk for obesity may be quite different between these two types of countries (16–18). A recent report from American Samoa, a low-income territory with a high prevalence of childhood obesity, suggests that breastfeeding may be protective against obesity in non-European populations (19). We examined the associations between breastfeeding and childhood body mass index (BMI) among 6- to 7-year-old children in the International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three. This programme was originally designed to measure time trends in the prevalence and severity of asthma, rhinoconjunctivitis and eczema, and to explore the relationship between lifestyle, other putative risk factors and the development of asthma and allergies. It also provided the opportunity to explore the relationship between factors such as breastfeeding and childhood BMI at age 6–7 years, as data on both these measures were collected.
Methods ISAAC is a multi-centre, multi-country, multi-phase crosssectional study investigating the prevalence of the symptoms of asthma, rhinoconjunctivitis and eczema, and the role of risk factors. ISAAC Phase Three was undertaken between 2000 and 2003 and involved 6- to 7-year-old children and 13- to 14-year-old adolescents chosen from a random sample of schools in a defined geographic area (20). It used a standardized core questionnaire on symptoms of asthma, rhinoconjunctivitis and eczema, and centres were encouraged to include an optional environmental questionnaire. The questionnaires were translated from English into the local language and then backtranslated into English where appropriate (21). The sampling framework and questionnaires are available on the ISAAC web site http://isaac.auckland.ac.nz. Parents and guardians of the 6- to 7-year-old participants were asked to report how much their child weighed, how tall they were and whether their child had been breastfed (yes or no). In some centres, each subject’s height and weight were measured objectively, although there were no standardized or specific instructions for doing this. BMI was calculated as kg m−2. Overweight and obesity were defined according to the revised International Obesity Task Force cut-off values for BMI (22). To be included in the analysis, centres had to assess at least 1000 subjects and have a response rate of >70% to the breastfeeding, height and weight questions. Individuals without complete data on sex, age, height, weight and breastfeeding were also excluded. To preserve as much remaining data as possible, but also eliminate likely erroneous data, we excluded those in the top and bottom 0.5% of weights and heights in each centre, and those with heights less than 1.0 m were excluded. Those with BMIs
© 2014 World Obesity. Pediatric Obesity ••, ••–••
214 706 subjects from 73 centres in 32 countries with data completed to ISAAC standards
Excluded: 919 subjects outside age range or no sex recorded
213 787 subjects from 73 centres in 32 countries
Excluded: 42 centres with
Association between breastfeeding and body mass index at age 6–7 years in an international survey R. J. Hancox1, A. W. Stewart2, I. Braithwaite3,4, R. Beasley3,4, R. Murphy5, E. A. Mitchell6 and ISAAC Phase Three Study Group*
Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, New Zealand; 2School of Population Health, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand; 3 Medical Research Institute of New Zealand, Wellington, New Zealand; 4Capital and Coast District Health Board, Wellington, New Zealand; 5Department of Medicine, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand; 6Department of Paediatrics: Child and Youth Health, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand
Summary
Address for correspondence: Dr RJ Hancox, Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, Dunedin 9053, New Zealand. E-mail: [email protected]
Results: Data were available for 76 635 participants from 31 centres in 18 countries. Reported breastfeeding rates varied from 27 to 98%. After adjusting for potential confounders, the estimated BMI difference was 0.04 kg m−2 lower among those who had been breastfed (P = 0.07). The risk for being overweight or obese was slightly lower among breastfed children (odds ratio = 0.95, P = 0.012). There was no evidence that the association between breastfeeding and BMI was different in lower income countries compared with higher income countries.
1
*Full listing of study group members appear at the end of this manuscript. Received 11 December 2013; revised 4 August 2014; accepted 2 September 2014
Background: Breastfeeding is believed to reduce children’s risk for obesity but data are conflicting. It is also uncertain if breastfeeding has different effects on obesity in high- and low-income countries. Objectives: This study aimed to investigate the association between having been breastfed and body mass index (BMI) in 6- to 7-year-old children in a large international survey. Methods: Parents/guardians reported whether their child had been breastfed and their current height and weight. Some centres measured height and weight directly. Analyses adjusted for whether height and weight were reported or measured, child’s age, sex, country gross national income and centre.
Conclusions: The findings suggest that breastfeeding has little impact on children’s BMI. Increasing breastfeeding is unlikely to reduce the global epidemic of childhood obesity. Keywords: Body mass index, breastfeeding, children, obesity. Abbreviations: BMI, body mass index; ISAAC, International Study of Asthma and Allergies in Childhood.
Introduction There is a widely held belief that breastfeeding children will help to prevent overweight and obesity later in life. Numerous observational studies and meta-analyses of these studies indicate a lower risk of overweight and obesity in those who have been breastfed (1–7), and biologically plausible mechanisms have been proposed to explain this protective effect (8). However, the effect of breastfeeding on risk for obesity remains controversial because the observational associations between breastfeeding and a lower risk for obesity may be subject to confounding by socioeconomic and other environmental factors (7,9–11). Moreover, the data available to systematic reviews and meta-analyses appear to have been influenced by publication bias and selective reporting of favourable findings (12).
© 2014 World Obesity. Pediatric Obesity ••, ••–••
A recent article described the belief that breastfeeding reduces the risk for obesity as a ‘myth’ – defined as a belief that persists despite substantial evidence that it is not true (13). The strongest evidence to support this view comes from the PROBIT study: a large cluster randomizedcontrolled trial promoting breastfeeding to women in Belarus (14,15). The intervention was effective in increasing duration of breastfeeding but did not find any evidence for reduced childhood obesity at ages 6.5 or 11.5 years among those who had been breastfed. A limitation of this study include the fact the PROBIT study recruited mothers who were intending to breastfeed, and thus most infants in the control group were breastfed to some extent. Moreover, the prevalence of obesity in children in Belarus was much lower than in many other countries reducing the power of the study to detect an association between breastfeeding and a lower risk for obesity.
ORIGINALRESEARCH
ORIGINALRESEARCH
ORIGINALRESEARCH
2
|
R. J. Hancox et al.
Most research on the association between breastfeeding and obesity has been performed in high-income rather than low- or middle-income countries. This is important because the confounding effects of the social and cultural determinants of breastfeeding practices and risk for obesity may be quite different between these two types of countries (16–18). A recent report from American Samoa, a low-income territory with a high prevalence of childhood obesity, suggests that breastfeeding may be protective against obesity in non-European populations (19). We examined the associations between breastfeeding and childhood body mass index (BMI) among 6- to 7-year-old children in the International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three. This programme was originally designed to measure time trends in the prevalence and severity of asthma, rhinoconjunctivitis and eczema, and to explore the relationship between lifestyle, other putative risk factors and the development of asthma and allergies. It also provided the opportunity to explore the relationship between factors such as breastfeeding and childhood BMI at age 6–7 years, as data on both these measures were collected.
Methods ISAAC is a multi-centre, multi-country, multi-phase crosssectional study investigating the prevalence of the symptoms of asthma, rhinoconjunctivitis and eczema, and the role of risk factors. ISAAC Phase Three was undertaken between 2000 and 2003 and involved 6- to 7-year-old children and 13- to 14-year-old adolescents chosen from a random sample of schools in a defined geographic area (20). It used a standardized core questionnaire on symptoms of asthma, rhinoconjunctivitis and eczema, and centres were encouraged to include an optional environmental questionnaire. The questionnaires were translated from English into the local language and then backtranslated into English where appropriate (21). The sampling framework and questionnaires are available on the ISAAC web site http://isaac.auckland.ac.nz. Parents and guardians of the 6- to 7-year-old participants were asked to report how much their child weighed, how tall they were and whether their child had been breastfed (yes or no). In some centres, each subject’s height and weight were measured objectively, although there were no standardized or specific instructions for doing this. BMI was calculated as kg m−2. Overweight and obesity were defined according to the revised International Obesity Task Force cut-off values for BMI (22). To be included in the analysis, centres had to assess at least 1000 subjects and have a response rate of >70% to the breastfeeding, height and weight questions. Individuals without complete data on sex, age, height, weight and breastfeeding were also excluded. To preserve as much remaining data as possible, but also eliminate likely erroneous data, we excluded those in the top and bottom 0.5% of weights and heights in each centre, and those with heights less than 1.0 m were excluded. Those with BMIs
© 2014 World Obesity. Pediatric Obesity ••, ••–••
214 706 subjects from 73 centres in 32 countries with data completed to ISAAC standards
Excluded: 919 subjects outside age range or no sex recorded
213 787 subjects from 73 centres in 32 countries
Excluded: 42 centres with
