Risk factors for onset and recurrence of MDD in Lifelines
Major depressive disorder (MDD) is an important contributor to the global burden of disease.(1–3) MDD can have major consequences over the entire lifespan, because it is often a chronic/recurrent disorder. For prevention and clinical practice, it is important to be able to know the most important risk factors for both first incidence and recurrence (4), as it could help to guide treatment and/or prevention strategies. For instance, in patients with a high risk of recurrence, it would seem reasonable to treat the depression as a chronic disorder (5) with antidepressants as maintenance treatment (6), whereas treatment of those with a low risk of recurrence could be limited to the index episode. In summary, if the most important risk factors for incidence and recurrence are known, subgroups could be selected that need either earlier interventions, more intensive treatment and/or longer-term treatment.
Prevalence data obtained in cross‐sectional studies are not suitable for investigating risk factors for either incidence or recurrence as they include a combination of new, recurrent and chronic disorders. In the last few decades, a number of longitudinal studies have been able to assess putative risk factors for the incidence and recurrence of MDD.(7–20) The factors that have been studied include childhood and lifetime adversity, stress, family history, psychiatric comorbidity, general/metabolic health status, lifestyle factors, sociodemographic data, psychosocial characteristics and, in the case of recurrence, clinical characteristics of the depressive disorder. The inference of risk factors for incidence and recurrence is complex; it is likely that multiple risk factors interact with one another, producing an aversive cascade of synergetic effects that can result in the occurrence of a depressive state.(21) Consequently, model development should focus not only on independent effects of predictors, but also on the combined effects of risk factors that together have a high overall explanatory value.
The investigation of this combination of risk factors is limited by the fact that many of the previous studies on risk factors for incidence and recurrence of MDD included only a limited number of predictors and/or a limited range of predictor types. Lifelines is a large general population cohort, in which a large number of internalizing disorders and risk factors have been assessed systematically.(22) Combined with Lifeline’s longitudinal design, this offers important opportunities to investigate the risk factors for incidence and recurrence of MDD. The aims of this study are to use Lifelines data to 1) determine both the first time incidence and recurrence rates of MDD and 2) estimate the associations of a broad range of different (clinical, psychosocial, environmental and lifestyle) risk factors with both incidence and recurrence of MDD.