DESCRIPTIVE EPIDEMIOLOGY OF MOOD DISORDERS
Mood disorders (e.g., depressive disorders, bipolar spectrum disorders) are leading causes of morbidity and mortality worldwide.1 The primary symptom feature of these group of psychiatric disorders are a disturbance in affect.2 Symptoms often first manifest in adolescence, but onset can occur throughout lifespan into later adulthood; appropriate diagnosis, particularly for bipolar spectrum disorders, may not occur until early adulthood. Mood disturbance can range from mild to severe, on a spectrum of depression to mania, and may be accompanied by psychosis.
This chapter takes a public health approach to mood disorders. This approach is one that emphasizes the role that “upstream” factors play in increasing (and decreasing) risk of mood disorders in the population. This includes the need for strategies to target the underlying causes of mental disorders from a systems perspective, one that recognizes how relatively weak but common risk (and protective) factors work together to shift population health outcomes.3 It is now appreciated that mood disorders, like most complex diseases, emerge from a pluripotent set of predictors; none of these factors, in and of themselves, is either necessary or sufficient to cause psychopathology. Recent decades have emphasized the population burden of mood disorders and the need to identify modifiable determinants of these conditions to and develop effective interventions.4
Major Depressive Disorder. Major depressive disorder (MDD) is the most prevalent mood disorder globally, affecting approximately 4.7% of the world’s population at any given time.1 MDD is a syndrome characterized by core feelings of sadness or low mood, and disinterest or anhedonia, accompanied by sleep disturbances (either sleeping too much or too little); changes in appetite or weight (either increases or decreases); fatigue or low energy; problems concentrating; psychomotor agitation or retardation; feelings of worthlessness, hopelessness or guilt; and preoccupation with death or suicidal thoughts.5,6 To have a MDD diagnosis, an individual must experience symptoms nearly every day for at least 2 weeks, and these symptoms must be associated with functional impairment. The 2012 revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), removed the so-called “bereavement exclusion” (i.e., a criterion stating if this syndrome developed immediately after death of a loved one, it would not qualify as MDD, but would instead be understood as a “normative” grief reaction); this change was the subject of intense scientific and philosophical debate.7
The projected lifetime risk MDD is 23.2%, with median age of onset at 32 years.8 However, many cases develop earlier in the life course. During childhood, the point prevalence of depressive episode is only 1–3%; however, this increases to 5–7% by adolescence and remains about this level throughout adulthood.9 There are significant sex differences in risk of MDD; women have significantly higher risk than men starting in adolescence. In a national survey, the cumulative incidence of MDD among females was 5.2% ...