Is Depression a Disease? -- Part III

Mainstream approaches to depression view it as resulting from a disease or defect (the defect can be biological or psychological). In my last post, I debunked several of the main arguments that are advanced in favor of the disease model.

In this post, (the last on this particular topic for a while) I consider some of the challenges of creating a better explanation of why people become depressed. Specifically, here are five key facts that an explanation of depression, must, somehow, explain. Again, these are facts that the disease model does not handle especially well, but I will not belabor that now.

(1) Syndromal and subsyndromal depression have extraordinarily high lifetime prevalence. Recent estimates project that up to 1/5th of the population will have an episode of major depression at some point. If one includes people who have significant depressive symptoms that fall just short of a diagnosis, about 40 percent of the population will have significant depression at some point in the life course. This is an extraordinarily high prevalence! When this high prevalence is coupled with the often young age of onset (late adolescence and early adulthood), one could say that the epidemiology of depression does not resemble that of a typical medical malady. Any explanation of depression must account for its extraordinarly high prevalence.

(2) Rates of depressive illness are accelerating. Good cross-cultural and cross-national evidence indicates that the prevalence of depression is increasing. This increase is a problem for the idea that depression reflects the operation of a fixed biological deficit (like a genetic defect), since the change in the prevalence of depression is occurring on a much more rapid timescale than could our biological makeup. And no, I do not think there is something in the water! Change in the psychological environment rather than the physical environment is the most likely candidate explanation.

(3) Depression is more prevalent in younger birth cohorts than in older birth cohorts. Again, there is strong epidemiological data that shows not only increasing rates of depressive illness overall, but that this acceleration is much more pronounced in young people. Several studies demonstrate that today's young adults have accumulated as much or more depression risk as people born much earlier (say people in their 50s and 60s). It is very unlikely that these effects are due to younger people simply being more comfortable reporting mild episodes of depression because of reduced depressive stigma. We see also increases in rates of very severe incapacitating depression in the young, including depression that requires hospitalization. The acceleration and concentration of illness among young people poses another challenge for defect models of depression.

(4) Depression is twice as common among adult females than adult males. Interestingly, we don't see this pattern in childhood. It emerges only in the middle-school years in adolescence. Again, if one holds to the defect model, one would have to explain why women have a special propensity to a deficit as well as why the deficit in question would come to light only at a particular stage in the life course. The gender difference in depression is one of the big facts of depression that has not been well-accounted for by most of the major models of depression.

(5) There are several empirically-supported treatments for depression but they appear to have plateaued in their effectiveness. The good news is that there are supported pharmacological and psychologically based treatments for depression (biological: antidepressants; psychological: cognitive-behavioral and interpersonal therapies). The bad news is that most of these treatments leave the majority of patients (even patients who respond) with residual symptoms. It is good that people are encouraged to seek treatment. However, one of the big facts of depression, which any good explanation of depression must explain is why the condition is often so recalcitrant to treatment. Once we acknowledge that depression is often treatment-refractory and focus efforts on explaining why this is, it will be much easier to develop treatments that manage the condition more effectively.