Early childhood exposure to maternal smoking and obesity: A nationwide longitudinal survey in Japan.

Involuntary exposure to tobacco smoke is suspected to be one of the risks factors that are associated with obesity in children. The purpose of this study was to examine the relationship between early childhood exposure to tobacco smoke and the risk of obesity and overweight in Japan. This study utilized a nationwide, population-based longitudinal survey. The participants were restricted to 32 081 children who had available information on maternal smoking history as well as childhood height and weight. We conducted a binomial log-linear regression analysis with children of non-smoking mothers as the reference group. The children with mothers who were smokers had a higher risk of developing obesity or being overweight compared to the children with mothers who were nonsmokers. The risk ratios were 1.20 (95% confidence interval [CI]: 1.09-1.32) for overweight and 1.17 (95% CI: 0.95-1.44) for obesity. Early exposure to maternal smoking increases the risk of being overweight and having obesity during childhood. The increased risk is more pronounced among children with mothers, smoked heavily, or parents, who were smokers.