Explaining inequalities in quality of life: a longitudinal study of health disparities in Norway

PURPOSE: Studies of health inequalities often examine the association between a single health indicator and a single socioeconomic indicator. Recent research has increasingly explored social disparities in self-reported quality of life. However, most evidences are based on cross-sectional survey and the role of health behaviours is frequently overlooked in these analyses. This study aims to integrate broader sets of socioeconomic and behavioural variables to better explain health disparities that emerge in later adulthood. METHODS: Using longitudinal data from the Norwegian population-based Tromsø Study, we followed 11,313 adults aged 25-54 at baseline over 21 years. A series of self-reported outcomes were studied, particularly EQ-5D-5L values, EQ-VAS scores, and Self-Rated Health. Predictors included three socioeconomic indicators (childhood living standard, own and spouse's educational attainment) and three health behaviours (smoking, physical activity, obesity). Shapley value decompositions were used to quantify each predictor's contribution to explained variance. RESULTS: For all three health outcomes, health behaviours accounted for the majority of the explained variance compared to socioeconomic factors: 80% for EQ-5D-5L, 75% for EQ VAS, and 67% for Self-Rated Health. When adjusting for differences in baseline health, the relative importance of health behaviours increased slightly. CONCLUSION: This study underscores the critical role of health behaviours in explaining inequalities in quality of life, providing new insights into the mechanisms driving these disparities. While preventing childhood deprivation would have significant impact on adult health, potential health benefits of promoting healthy behaviours are substantial. Both types of policy interventions could thereby contribute to reducing health inequalities.