Exposure to secondhand smoke, exclusive breastfeeding and infant adiposity at age 5months in the Healthy Start study

BackgroundInfant adiposity may be influenced by several environmental risk factors, but few studies have explored these interactions. ObjectiveTo examine the interaction between exposure to secondhand smoke and breastfeeding exclusivity on adiposity at age 5months. MethodsWe studied 813 mother-offspring pairs from the longitudinal Healthy Start study. Fat mass and fat-free mass were measured by air displacement plethysmography. Linear regression analyses were used to estimate the association between household smokers (none, any) with fat mass, fat-free mass, percent fat mass, weight-for-age z-score, weight-for-length z-score and BMI-for-age z-score as separate outcomes. Interaction terms between household smokers and breastfeeding exclusivity (<5months, 5months) were added to separate models. ResultsThe combination of exposure to secondhand smoke and a lack of exclusive breastfeeding was associated with increased adiposity at age 5months. For example, within the not exclusively breastfed strata, exposure to secondhand smoke was associated with increased fat mass (0.1kg; 95% CI: 0.0-0.2; P=0.05). Conversely, within the exclusively breastfed strata, there was virtually no difference in fat mass between exposed and non-exposed infants (coefficient: -0.1; 95% CI: -0.3-0.1; P=0.25). ConclusionsOur findings may inform new public health strategies with potential relevance for both smoking cessation and obesity prevention.