Is Depression Psychological, Physical, or Both?

Depression is both psychological and physical.

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Is depression physical or mental?

The apparent dichotomy between "physical" and "mental" illnesses taps into one of the deepest conceptual fault lines in psychiatry and psychology, which is the spurious division between "physical" and "mental" phenomena. Depression is a perfect example of this.

Described aloud, depression sounds like a very psychological phenomenon: low mood, guilt, hopelessness, and suicidality. But people with severe depression often tell me that depression runs much deeper than very severe unhappiness: It is also a bodily condition characterized by a profound physical slowing down, loss of energy, and disturbances to appetite, sleep, movement, sexual activity, and other biological functions.

In other words, depression affects the entire physical body and not just the brain or mind.

This makes perfect sense: There is no logical division between mental and physical phenomena. Our brains are as much a part of our body as our arms and legs are. It is illogical to think that physical factors would not affect our mental health, and that mental factors would not affect our physical health.

This close interaction between our mental and physical selves is clearly evidenced in our current understandings of the causes of depression, which include not only mental and physical risk factors but also social circumstances that create the overall landscape of risk for the disorder.

Stressful life events are often contributory causes and precursors of depression: childhood neglect, becoming unemployed, financial difficulties, relationship problems, abuse, and being the victim of violence.

What happens biologically when people get depressed

From a biological perspective, it is possible that these effects are mediated through the body’s stress response mechanism, especially the hormone cortisol, which can be constantly "switched on" by chronic stress. This damages virtually all body organs, including the brain.

It is also clear that the activity of certain brain chemicals (serotonin, noradrenaline, and dopamine) can be disordered in depression, although it is not clear to what extent this is true for everyone and what it actually means. Cause and effect can be difficult to untangle.

It is, of course, inevitable that various changes in brain chemistry would be associated with depression, not least because such changes are associated with every mood state we experience, every thought we think, and everything we perceive in the world.

But it would be misleading to suggest that such chemical changes are either fully understood or fully identified as causes of depression, rather than consequences. The reason for this uncertainty is the simple fact that, despite an enormous amount of neuroscientific research, we simply do not fully understand how the brain works even when it is having a good day, let alone when a person is depressed or suicidal.

The brain is infinitely complex, and it is possible that we will never understand it fully. Physicist Emerson Pugh is credited with the idea that if the brain were so simple that we could understand it, we would be so simple that we couldn’t.

To summarize what we know, it is now established that the human brain includes around 86 billion nerve cells, the biological "building blocks" of life. The brain also has many billions of other types of cells that nourish and support the all-important nerve cells and make up the rest of an organ that is the most complex, miraculous, and infuriating object on the planet.

Somehow, the brain manages to be both the cause of virtually all human progress and the cause of virtually all human suffering. It is also part of the solution.

The reason for this situation lies in the enormous complexity and immaculate organization of the brain. Each of the brain’s 86 billion nerve cells communicates with thousands of other brain cells using a range of different chemicals passing across tiny gaps between cells called "synapses." The resulting patterns of communication across the brain are infinitely variable because there are between 100 trillion and 1,000 trillion connections between brain cells, all firing in different ways, at different strengths, at different times, and in different combinations.

The mind, literally, boggles—even when we sleep.

Against this background, it is not surprising that (a) the human brain is so complex as to defy human understanding to date; (b) the "normal" brain is a very variable thing, and its activities change constantly, even within the same person, let alone between people; and (c) the biological correlates of what we experience as depression are incredibly complex, highly variable over time, and might well differ from person to person. The fact that the brain changes over time in response to internal and external stimuli (aka "neuroplasticity") adds yet another layer of complexity.

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All that being said, depression does seem to be associated, albeit inconsistently, with certain changes in brain chemistry (especially relating to the brain chemical serotonin), disordered cortisol levels, and certain indicators of chronic inflammation, as well as—less convincingly—minor changes in brain structure and the effects of specific genes inherited from our parents.

It is known that depression tends to run in families, but research to date has identified only genes of small effect in certain people, so the precise mechanisms whereby some families have increased risk of depression and other mental illnesses is not yet known.

In sum

The language of biology (brain cells, nerves, hormones, genes, etc.) is currently inadequate in certain ways in its understanding and description of depression, so the language of psychology holds greater relevance and appeal for many people. This is centered on childhood experiences, chronic stress, traumatic life events, cognitive habits, and various psychological and social factors.

These factors appear to increase the risk of depression. Awareness of them can help with explaining, problem-solving, and, most of all, healing.

Antidepressants are highly effective in depression—and so is understanding.