Time‐varying exposure and the impact of stressful life events on onset of affective disorder

Abstract

Stressful life events are now established as risk factors for the onset of affective disorder but few studies have investigated time-varying exposure effects. Discrete (grouped) time survival methods provide a flexible framework for evaluating multiple time-dependent covariates and time-varying covariate effects. Here, we use these methods to investigate the time-varying influence of life events on the onset of affective disorder. Various straightforward time-varying exposure models are compared, involving one or more (stepped) time-dependent covariates and time-dependent covariates constructed or estimated according to exponential decay. These models are applied to data from two quite different studies. The first, a small scale interviewer-based longitudinal study (n = 180) concerned with affective disorder onset following loss (or threat of loss) event experiences. The second, a questionnaire assessment as part of an ongoing population study (n = 3353), provides a history of marital loss events and of depressive disorder onset. From the first study the initial impact of loss events was found to decay with a half-life of 5 weeks. Psychological coping strategy was found to modify vulnerability to the adverse effects of these events. The second study revealed that while men had a lower immediate risk of disorder onset following loss event experience their risk period was greater than for women. Time-varying exposure effects were well described by the appropriate use of simple time-dependent covariates.

The moderation by the serotonin transporter gene of environmental adversity in the aetiology of mental illness: review and methodological analysis

“…125 Research into the role of stressful life events and difficulties in the causation of depression has a long history. 126,127 It has been established that stressful life events (SLE) have a causal role in the genesis of depression, 128 their depressogenic effect is variable and depends on the level of 'contextual threat', 126 they are closely related in time to the onset of depression 129,130 and have stronger effect on first onset of depression than on recurrences. 61 The effect of SLE is not specific to depression as they are also associated with the onset of anxiety disorders, 131 substance abuse, 132 eating disorders 133 and psychosis.…”

“…138 The duration of the depressogenic effect of SLE also differs by gender: effect of marital loss decays with a half-life of 5 months in women and half-life of 21 months in men. 130 In the 5-HTTLPR G Â E studies, the time period for recording life events varied from 3 months 15 to 5 years. 11 In one small G Â E study, the G Â E interaction was significant for SLEs over five years but not for SLEs in the one year preceding the depression onset.…”

The role of life events and psychological factors in the onset of first and recurrent mood episodes in bipolar offspring: results from the Dutch Bipolar Offspring Study

“…Overall, we calculated three different types of life event measures: cumulative load (CLEL); cumulative load excluding events related to psychopathology of the respondent (CLEL-NoPsy); and cumulative load including only independent events (CLEL-Ind). Taking into account a possible decay effect of life events over time, a time-specific life event load was subjected to an exponential decay function (Wainwright & Surtees, 2002). We tested four models: model I tested a purely cumulative effect of life events (= CLEL); model II the decay function implied a 25% loss of CLEL per year; model III the decay function implied a 50% loss of CLEL per year; and model IV the decay function implied a 75% loss of CLEL per year.…”

Life stressors and 5-HTTLPR interaction in relation to midpregnancy depressive symptoms among African–American women

“…While individuals with elevated depressive symptoms may be more likely to recall stressful life events, we do not expect this recall to vary systematically by genotype and explain the gene-environment interaction we observed. Investigators (Kendler et al , 1998, Wainwright and Surtees, 2002) have asserted that recent exposures to stressful life events present a higher risk for developing a depressive episode than do distant events. Ideally models of depression risk would take into account many factors including recent and distant stressful events, personality characteristics, prior history of depression and gender (Kendler et al , 2002, Kendler et al , 2006).…”