Maternal smoking, breastfeeding, and risk of childhood overweight: findings from a national cohort.

To examine the association between exposure to tobacco compounds in breast milk and risk of childhood overweight, we used historical data for a subset of 21,063 mother-child pairs in the US Collaborative Perinatal Project. Based on self-reports, mothers were classified as non-smokers, light (1-9 cigarettes/day), moderate (10-19), or heavy (20+) smokers. Feeding type (exclusive breastfeeding or bottle-feeding) was observed during nursery stay after birth. We stratified children by maternal smoking and feeding type, and then fit interaction terms to isolate exposure to tobacco compounds via breast milk from exposure in uterus and in ambient air after birth. Using measured weight and height, overweight at age 7 was defined as a body mass index ≥85th percentile by sex and age. Among exclusively bottle-fed children, adjusted odds ratios (ORs) of overweight at age 7 were 1.24 (95% confidence interval [CI], 1.12-1.38; vs. non-smoking) for light maternal smoking, 1.43 (95% CI, 1.25-1.63) for moderate maternal smoking, and 1.46 (95% CI, 1.28-1.66) for heavy maternal smoking. Among exclusively breastfed children, the corresponding ORs were 1.33 (95% CI, 0.96-1.84) for light, 1.86 (95% CI, 1.27-2.73) for moderate, and 2.22 (95% CI, 1.53-3.20) for heavy maternal smoking. There was a modest positive interaction between breastfeeding and heavy maternal smoking on overweight risk at age 7. Tobacco compounds via breast milk of smoking mothers (significantly for heavy smokers) appear to be associated with a modest elevation in childhood overweight risk at 7 years of age. More aggressive intervention is needed to help pregnant and breastfeeding women to quit smoking.