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More Evidence of the Protective Effect of Breastfeeding Against Childhood Obesity

The question of whether a protective effect against childhood obesity can be confidently added to the growing list of the benefits of breastfeeding has been explored for a number of years. Prior to 1999, most published studies examining this relationship had inadequate sample size to detect a difference in prevalence of overweight between feeding groups and/or grouped all “ever breastfed” infants together, thus failing to consider amount of exposure to breastfeeding. The latter is an important consideration as the “dose” of breast milk varies considerably, depending on breastfeeding duration and exclusivity. Not surprisingly, the results of these early studies were mixed, with the question of whether there is a protective effect of breastfeeding on child obesity remaining unanswered. However, since 1999, several better quality studies have been published, allowing greater clarity on the issue. Recognizing this development in the evidence base, Dewey conducted a literature review on the protective effect of breastfeeding on childhood obesity, focusing on studies with adequate sample size and other qualities of sound study design. Of the 11 studies meeting her review criteria, 8 showed a lower risk of overweight among children who had been breastfed. A common feature of all 3 studies that failed to show a lower risk was lack of consideration of exclusivity of breastfeeding. However, despite newer research in this area suggesting a protective effect of breastfeeding on childhood overweight, the generally low representation among low-income and nonwhite cohorts in the studies restricts the generalizability of the findings. The evidence base also lacks adequate representation in the longer breastfeeding duration categories, resulting in an inability to significantly detect clinically important differences as dose of breastfeeding increases. The study spotlighted in this issue of JHL builds on the existing evidence by using data from the US Pediatric and Pregnancy Nutrition Surveillance Systems. The data represent 177,304 ethnically diverse low-income children who were enrolled in the Supplemental Food Program for Women, Infants, and Children (WIC) with additional maternal data available from a subset (12,587) via linking to the Pregnancy Nutrition Surveillance System. The main outcome variable, overweight status at 4 years of age, was defined as body mass index (BMI) for age at 4 years > 95th percentile. Exposure to breastfeeding was based on twice-yearly maternal report of breastfeeding duration through the first 2 years of the infant’s life. No information regarding breastfeeding exclusivity was recorded. Other lifestyle factors that co-vary with breastfeeding behavior may contribute to childhood obesity risk. Thus, it is important to control for these potential confounders. In the larger sample, data were available for gender, ethnicity, and birth weight. Among the subset with links to the Pregnancy Surveillance System, additional variables controlled for were maternal age and education, prepregnancy BMI, weight gain during pregnancy, and postpartum smoking. Fifty-two percent of the larger cohort were white, non-Hispanic; 29% were black, non-Hispanic; and 14% were Hispanic (5% other). The majority of participants were never exposed to breastfeeding (71%). Ten percent breastfed < 1 month, 8% 1 to 2.9 months, 5% 3 to 5.9 months, 4% 6 to 11.9 months, and only 2% were breastfed for 12 months or more. The overall prevalence of overweight was 13.3%.