Observed associations between indicators of socioeconomic status and risk of multiple sclerosis in Sweden are explained by a few lifestyle‐related factors

Background and purpose The association between socioeconomic status (SES) and the risk of multiple sclerosis (MS) is unclear. The aim was to study whether a potential association between indicators of SES and MS risk in Sweden is explained by lifestyle/environmental factors. Methods Using the Swedish MS registry and the Swedish patient registries, a register study was performed comprising all cases diagnosed with MS in Sweden between 1990 and 2018 (N = 24,729) and five randomly selected controls per case, matched by year and age at disease onset, sex and residential area at disease onset. Data from two matched case–control studies combined comprising data on environment/lifestyle factors (7193 cases, 9609 controls, inclusion period 2005–2018) were also utilized. For all participants, information regarding ancestry, formal education (available 1990–2018) and family income (available 1998–2018) was retrieved from the National Board of Health and Welfare. Results The registry study revealed no association between education and MS risk, whereas an income exceeding the upper quartile was associated with lower MS risk compared to having an income in the lowest quartile (odds ratio 0.86, 95% confidence interval 0.82–0.90). These findings were replicated in the crude analyses of the case–control study. However, after adjustment for confounding, no association was observed between income and risk of MS. Conclusions Education and income were not associated with occurrence of MS after adjustment for a few lifestyle‐related factors (smoking, alcohol consumption, body mass index and sun exposure habits), indicating that SES has no influence on MS risk besides its association with these lifestyle factors in the Swedish context.