The association between indoor temperature and body mass index in children: the PIAMA birth cohort study

Background: Several experimental studies showed consistent evidence for decreased energy expenditure at higher ambient temperatures. Based on this, an association between thermal exposure and body weight may be expected. However, the effect of thermal exposure on body weight has hardly been studied. Therefore, this study investigated the association between indoor temperature and body mass index (BMI) in children in real life. Methods: This longitudinal observational study included 3 963 children from the Dutch Prevention and Incidence of Asthma and Mite Allergy (PIAMA) birth cohort that started in 1996. These children were followed from birth until the age of 11 years. Winter indoor temperature (living room and bedroom) was reported at baseline and BMI z-scores were available at 10 consecutive ages. Missing data were multiply imputed. Associations between indoor temperature and BMI were analyzed using generalized estimating equations (GEE), adjusted for confounders and stratified by gender. In a subgroup of 104 children, bedroom temperature was also measured with data loggers. Results: Mean reported living room and bedroom temperature were 20.3 degrees C and 17.4 degrees C, respectively. Reported and measured bedroom temperatures were positively correlated (r = 0.42, p = 0.001). Neither reported living room temperature (-0.03 <= beta >= 0.04) and bedroom temperature (-0.01 <= beta >= 0.02) nor measured bedroom temperature (-0.04 <= beta >= 0.05) were associated with BMI z-score between the age of 3 months and 11 years. Conclusions: This study in children did not support the hypothesized association between indoor temperature and BMI in a real life setting.