Life Stress and Mental Disorders in the South African Stress and Health Study (Original Articles) (Report‪)‬

The role of stressful life events (SLEs) in the pathogenesis of mental disorders is not well understood. Individuals vary greatly in their response to SLEs, with some more susceptible to morbidity than others in the face of adversity. This phenotypic variance is accounted for by genetic and individual-specific environmental factors. (1) It has been suggested that SLEs that are largely dependent on an individual's own behaviour are more heritable than 'fateful' events that are independent of an individual's actions. (2) Twin studies have provided the strongest evidence of the magnitude of effect of the environment relative to genes, with environmental stressors contributing as much of the variance to a disorder, such as depression, as genetic influences. (3) SLEs can herald the onset of depression and/or affect the symptom profile, expression, course (e.g. illness duration, symptom exacerbation), treatment and outcome. (4-7) They are characterised as those of recent onset and those that occurred early in life. Recent or proximal events (e.g. death or illness in the family, interpersonal violence, financial difficulties) have commonly been associated with risk of mood and anxiety disorders. (8-11) Past studies have also linked distal events, such as adversities in childhood (e.g. parental death/separation/divorce), to the onset of common mental disorders in adulthood. (8,12) A central question is the relationship of early adversity to more recent events in the onset of psychiatric disorders. Evidence suggests that childhood adversity, when combined with current stressors, increases vulnerability to adult depression by 3.5-11-fold. (12) This has been proposed to occur through sensitisation of stress-responsive neurobiological systems (e.g. the hypothalamicpituitary-adrenal axis) as a consequence of early-life stress which may, in turn, be moderated by specific genetic variants (polymorphisms). (1,13,14) The resulting sensitisation in individuals who have experienced significant childhood adversity may lead to a heightened reactivity to subsequent stress such that lower levels of stress may trigger the onset of a depressive episode. (15,16)