Intelligence level in late adolescence is inversely associated with BMI change during 22 years of follow-up: results from the WICTORY study

The objective of this population-based retrospective cohort study was to examine the association between intelligence (IQ) at late adolescence and changes in body mass index (BMI) during 22 years of follow-up until 40 years of age, taking education level into account. Data from 5,286 males born 1950–1959 who had participated in the Westmannia Cardiovascular Risk Factors Study at 40 years of age and attended the Swedish military conscription examination between the ages of 17 and 22 were used. From a mean age of 18 years until follow-up at 40 years of age, BMI increased with a mean (95 % confidence interval (CI)) of 4.36 (4.28–4.43) kg/m², equalling 0.20 kg/m² per year. The difference in BMI change between IQ levels was strongly statistically significant (P < 0.001), with a strictly inverse relationship between IQ and BMI change. The lowest IQ level (<74) had a mean (95 % CI) BMI increase of 5.19 (4.63–5.74) kg/m², equalling 0.24 kg/m² per year, compared with 3.73 (3.40–4.07) kg/m², equalling 0.17 kg/m² per year, for the highest IQ level (>126). Education level also had a strictly inverse relationship with BMI change. After adjusting for confounding variables, including education level, IQ still had a strictly inverse relationship to BMI change, with all IQ levels < 111 having a significantly larger BMI change than IQ > 126 (P < 0.01 for all levels). Education level at 40 years of age but not at 18 years of age had a significant association with BMI change after adjusting for IQ.