The moderating effect of income on the relationship between body mass index and health-related quality of life in Northern Sweden

Abstract

Objectives: This study aimed to investigate the relationship between body mass index (BMI) and health-related quality of life (HRQoL) and whether this relationship is influenced by the level of income in Northern Sweden. Overweight and obesity are rising major public health problems which also affect HRQoL. While socioeconomic inequalities in health are persisting or increasing in many countries, including Sweden, little attention has been paid to the more complex roles of income in relation to health. Methods: Data were drawn from a 2014 cross-sectional survey from Northern Sweden (Health on Equal Terms), comprising individuals aged 20–84 years (N = 20,082 individuals included for analysis). BMI and HRQoL were self-reported and individual disposable income in 2012 was retrieved from population registers. Multiple linear regressions were performed with HRQoL scores regressed on BMI and income, their interaction and additional covariates. Results: The underweight, overweight and obesity groups reported significantly lower HRQoL compared to the normal weight group. Moreover, the relationship between BMI and HRQoL varied significantly by level of income, with a stronger association among those with the lowest level of income. Conclusions: Income has a role as an effect modifier in the relationship between BMI and HRQoL that can be construed as an indirect income inequality. Efforts to promote HRQoL in populations should consider the different impact of being overweight and obese in different socioeconomic groups.