Childcare Attendance and Obesity Risk.

BACKGROUND AND OBJECTIVES Several observational studies have revealed that children who receive nonparental childcare are at increased risk of obesity. However, this may be due to unmeasured confounding or selection into different types of childcare. It is not well established whether this association reflects a causal effect of childcare attendance on obesity risk. We examined the effect of attending childcare on children's BMI z scores, using nationally representative data of ∼10 700 children followed from age 9 months through kindergarten entry. METHODS We first employed ordinary least squares regression to evaluate longitudinal associations between childcare attendance at 24 months and BMI z scores at kindergarten entry, controlling for child, family, and neighborhood characteristics. Because type of childcare is associated with unobserved confounding factors, we repeated the analysis by using 2 quasi-experimental approaches: (1) individual fixed effect models, which control for all observed and unobserved time-invariant confounders; and (2) instrumental variable (IV) analysis. RESULTS At 24 months, 48.7% of children were in nonparental childcare, and 35.1% of children were overweight/obese at kindergarten entry. In ordinary least squares models, compared with children in parental care, children in nonparental childcare at 24 months had higher BMI z scores at kindergarten entry (0.08 [SE 0.03], P = .01). By contrast, fixed effects and IV models revealed no significant effect of childcare on BMI z score (fixed effects model: β = 0.02 [SE 0.02], P = .62); IV model: β = 1.12 [SE 0.76], P = .14). CONCLUSIONS We found no consistent associations between nonparental childcare and obesity. Previously reported significant associations may be confounded by unobserved family circumstances resulting in selection into different types of childcare.