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Can breastfeeding help prevent overweight children and adolescents?

 

The number of overweight children, adolescents and adults is rising markedly. Obesity in children and adolescents predicts obesity in adult life, it predicts morbidity and mortality decades later, it is associated with cardiovascular risk factors, orthopaedic conditions and lower self-esteem and once present it is hard to treat. Preventing obesity is therefore of primary concern. These two studies examine the possibility that breastfeeding may reduce the risk of overweight in childhood and adolescence.

Message

The two studies disagree whether breastfeeding can reduce the risk of overweight in children. However, considering both studies, it may be the combination of mothers breastfeeding with having an optimum body mass index (implicating sharing healthy lifestyle habits with their children such as diet and physical activity) that reduces the risk of childhood overweight. Breastmilk is already acknowledged as the best food for babies, giving unique immunological, growth and developmental benefits. If there is a chance that it can help prevent childhood obesity then this should be promoted, paying special attention to overweight mothers who are less likely to breastfeed and may need additional support with initiating and maintaining breastfeeding.

Study 1

Reference

MW Gillman et al. Risk of overweight among adolescents who were breastfed as infants. Journal of the American Medical Association 2001 285: 2461-2467.

Study

Participants were 15,341 children (8,816 girls and 7,155 boys) aged 9 to 14 years from the Growing Up Today Study (investigating diet, activity and growth) with no medical conditions that could have interfered with their growth and whose gestation period was not less than 34 weeks.

Questionnaires were sent to the children in 1996 ascertaining information on demographic characteristics, height, weight, sexual maturity, diet and physical activity for the previous 12 months and time spent watching television. Questionnaires were sent to their mothers (who were participants in the US Nurses’ Health Study) in 1997 obtaining information on their children’s early life including birth weight, length, gestational age, medical conditions and method of feeding. The questions on feeding included the main liquid feeding method in the first six months (breast milk only, more breast milk than formula, both equally, more formula than breast milk and formula only) and the duration of breastfeeding. Additional information on the mothers’ lifestyle habits (e.g. smoking, diet and physical activity) was obtained from the Nurses’ Health Study questionnaires.

The effect of (i) breastfeeding in the first six months and (ii) duration of breastfeeding on being overweight in adolescence was examined. Overweight was defined as a body mass index above the 95th percentile for age and gender from a national sample of US children. The 95th percentile corresponds to a body mass index of 30 kg/m2 or grade 2 overweight in adults.

Results

The average age of the children was 11.9 years; 94% were white; and 5% of the girls and 9% of the boys were overweight. In the first six months, 9,553 children (62%) were only or mostly fed breast milk and 4,744 (31%) were only or mostly fed formula. While 7,186 children (48%) were breastfed for at least seven months, 4,613 (31%) were breastfed for three months or less.

Breast versus formula feeding

Adolescents who were mostly or only fed breast milk in the first six months had a 22% lower risk of being overweight (odds ratio 0.78, 95% confidence interval 0.66 to 0.91) than adolescents who were mostly or only fed formula. These results were adjusted for the childrens’ age, sex, sexual maturity, energy intake, time spent watching television, physical activity, birth weight and birth order; the mothers’ body mass index, smoking, dietary restraint and weight cycling; and estimated household income.

Duration of breastfeeding

Adolescents who were breastfed for at least seven months were 20% less likely to be overweight than those breastfed for three months or less (odds ratio 0.80, 95% confidence interval 0.67 to 0.96). These results were adjusted as above.

There was an estimated 8% reduction in the risk of adolescent overweight for every additional three months of breastfeeding (with the highest category being nine months or more) (odds ratio 0.92, 95% confidence interval 0.87 to 0.98).

Maternal body mass index

Mothers who fed their babies only breast milk in the first six months had the lowest average body mass index (24.5 kg/m2). Mothers who fed their babies only formula had the highest average body mass index (25.7 kg/m2).

Mothers who breastfed their babies for a longer period had a lower average body mass index than mothers who breastfed for shorter periods, e.g. mothers who breastfed for at least seven months had an average body mass index of 24.6 kg/m2 compared with 25.7 kg/m2 for mothers who breastfed for three months or less.

Mothers’ body mass index predicted their childrens’ weight. Mothers with a body mass index of more than 30 kg/m2 were 27% more likely to have an overweight adolescent than mothers whose body mass index was less than 25 kg/m2 (odds ratio 0.27, 95% confidence interval 0.21 to 0.33).

Study 2

Reference

ML Hediger et al. Association between infant breastfeeding and overweight in young children. Journal of the American Medical Association 2001 285: 2453-2460.

Study

Participants were 2,685 children (1,375 girls and 1,310 boys), aged 3 to 5 years, who had not had special neonatal care or a very low birthweight (less than 1,500 g). The children were from the National Health and Nutrition Examination Survey III conducted between 1998 and 1994. Birth details were taken from their birth certificates (e.g. birth order and weight, length of gestation). Demographic and maternal characteristics were obtained from the survey and included smoking habits and body mass index. Additional questions on feeding included whether the child was breastfed or formula fed, at what age and for how long. Children were classified as never breastfed or fully breastfed (with no supplementation of formula). Their weight and height were measured directly and body mass index calculated. Overweight was defined as a body mass index above the 95th percentile.

Results

Breastfeeding

There was no reduced risk of being overweight if breastfed (odds ratio 0.84, 95% confidence interval 0.62 to 1.13). The results were adjusted for the childrens’ gender, birth weight, race/ethnicity, the mothers’ body mass index and when solid foods were introduced.

Maternal body mass index

Over 50% of overweight and obese mothers did not breastfeed.

Mothers’ body mass index predicted their childrens’ weight. Overweight in childhood was nearly three times greater with maternal overweight (odds ratio 2.95, 95% confidence interval 1.35 to 6.42) and more than four times greater with maternal obesity (odds ratio 4.34, 95% confidence interval 2.50 to 7.54).

Comment

Gillman et al’s study found that breastfed babies are less likely to become overweight adolescents than formula fed babies and the protective effects are larger with longer periods of breastfeeding. In contrast, Hediger et al’s study did not find any association between breastfeeding and subsequent obesity.

The participant and study characteristics of these two studies are very different, all of which affect results (e.g. 15,341 versus 2,685 children; 9 to 14 years versus 3 to 5 years, white versus ethnically diverse). The absence of a breastfeeding effect in Hediger et al’s study may be attributable to the small number of participating children or that the consequences of different feeding methods may not become apparent until later childhood for example. Gillman et al’s study was much larger and the associations remained significant after adjusting for numerous potentially influential factors on childrens’ weight.

The mechanism by which breastfeeding may protect against later overweight and obesity is unclear. For example,

In both studies maternal obesity is related to childhood/adolescent obesity implicating the role of genetic and environmental factors, such as shared lifestyle habits, e.g. diet and physical activity patterns.

The finding that overweight and obese mothers were less likely to breastfeed (perhaps because maternal adiposity prevents successful initiation or maintenance of breastfeeding) provides a further suggestion that it is a combined effect of maternal overweight with the absence of breastfeeding that results in an increased risk for becoming overweight in later years.