Socioeconomic differences in major depressive disorder onset among adults are partially explained by lifestyle factors: A longitudinal analysis of the Lifelines Cohort Study

Background: Major depressive disorder (MDD) onset varies by socioeconomic position (SEP), this could be explained by lifestyle factors, but little is known about this pathway. Our study aims to disentangle the interplay between SEP measures (i.e., education, income and occupational prestige) and MDD onset and to examine to what extent these associations are mediated by lifestyle (i.e., occupational- and leisure time physical activity, smoking, alcohol intake, diet quality, sleep and central adiposity). Methods: A subsample (n = 76,045) of the Lifelines Cohort Study without MDD at baseline was included. MDD onset was measured after a median follow-up time of 3.8 years with the Mini International Neuropsychiatric Interview (MINI). Direct associations between SEP, lifestyle and MDD onset were estimated using logistic regression analyses. Mediating percentages were estimated using the Karlson-Holm-Breen method. Results: 1864 participants (2.5 %) showed MDD at follow-up. SEP was inversely associated with MDD onset, with education showing the strongest association. Educational, income and occupational differences in MDD onset were for 18.7 %, 5.9 % and 21.7 % explained by lifestyle factors (mainly smoking, alcohol intake and central adiposity). Limitations: SEP and lifestyle factors were measured simultaneously at baseline. MDD status (only based on a screening tool) was only measured at baseline and 3.8 years later. Conclusions: Compared to their lower SEP counterparts, higher SEP individuals had a lower risk of MDD onset. This was partially explained by a healthier lifestyle (mainly less smoking, alcohol intake and central adiposity) of the higher SEP individuals.