Physical activity attenuates the effect of low birth weight on insulin resistance in adolescents: findings from two observational studies

OBJECTIVE: To examine whether physical activity influences the association between birth weight and insulin resistance in adolescents. RESEARCH DESIGN AND METHODS: The study comprised adolescents who participated in two cross-sectional studies: the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) study (n = 520, mean age = 14.6 years) and the Swedish part of the European Youth Heart Study (EYHS) (n = 269, mean age = 15.6 years). Participants had valid data on birth weight (parental recall), BMI, sexual maturation, maternal education, breastfeeding, physical activity (accelerometry, counts/minute), fasting glucose, and insulin. Insulin resistance was assessed by homeostasis model assessment-insulin resistance (HOMA-IR). Maternal education level and breastfeeding duration were reported by the mothers. RESULTS: There was a significant interaction of physical activity in the association between birth weight and HOMA-IR (logarithmically transformed) in both the HELENA study and the EYHS (P = 0.05 and P = 0.03, respectively), after adjusting for sex, age, sexual maturation, BMI, maternal education level, and breastfeeding duration. Stratified analyses by physical activity levels (below/above median) showed a borderline inverse association between birth weight and HOMA-IR in the low-active group (standardized β = -0.094, P = 0.09, and standardized β = -0.156, P = 0.06, for HELENA and EYHS, respectively), whereas no evidence of association was found in the high-active group (standardized β = -0.031, P = 0.62, and standardized β = 0.053, P = 0.55, for HELENA and EYHS, respectively). CONCLUSIONS: Higher levels of physical activity may attenuate the adverse effects of low birth weight on insulin sensitivity in adolescents. More observational data, from larger and more powerful studies, are required to test these findings.This work was mainly supported by the European Community Sixth RTD Framework Programme (Contract FOOD-CT-2005-007034) and by grants from the Stockholm County Council. This study was also supported by grants from the Spanish Ministry of Education (EX-2008-0641, AP2006-02464), the Swedish Heart-Lung Foundation (20090635), the Swedish Council for Working Life and Social Research (Forskningsrådet för arbetsliv och socialvetenskap [FAS]), the Spanish Ministry of Health: Maternal, Child Health and Development Network (Number RD08/0072), and the Spanish Ministry of Science and Innovation (RYC-2010-05957)