Obesity and sex- and age-specific income – evidence from the HUNT study

Abstract

Abstract Background Elevated body mass index (BMI) has been found to be associated with lower income, especially among women, and increasing evidence suggests that this association is causal. However, there is limited knowledge about the sex-specific effect of BMI on income at different ages. The relationship between BMI and income may change with age due to, for example, BMI-related morbidities or discrimination. The aim of this study was to investigate the sex-specific causal link between BMI and income at different ages. Methods The age-, and sex-specific effects were estimated using an instrumental variable approach with genetic variants as instruments (i.e., Mendelian randomisation) in an effort to deal with reverse causality and omitted variables that may bias the relationship between BMI and income. We also reduced measurement error by using registry-based income and clinically measured height and weight. Findings Elevated BMI led to a reduced likelihood of working, and lower income. For females, increased BMI led to lower income throughout, and particularly at the end of, work life. For males, increased BMI led to lower income from age 49 onwards.