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The Biological Causes of Depression

A combination of poor mood, self-doubt, and physical pain, depression can be an agonizing experience. The good news is that most people can find at least partial, if not complete, relief from their symptoms. To better understand your symptoms and how depression therapies work, it can be helpful to learn about the various causes of depression.

We don’t know yet which of the following factors are necessary or sufficient to cause a clinical course of depression. Given the proliferation of research data and partially compelling arguments, many Utah researchers and clinicians now believe that there are at least a couple different ways in which individuals may be vulnerable to a persistently depressed mood.

With this in mind, if you’re just starting to learn about depression in Utah, we recommend that you also read our summary of the psychosocial causes of depression. Here, we stick to a synopsis of the biological explanations, which are pretty much the same no matter where you live.

 

Biological Causes of Depression

Monoamine Neurotransmitters: Here’s the three-sentence summary for all the information out there about “chemical imbalances in the brain.” Monoamine oxidase is a family of enzymes that serve as the catalyst for the oxidation and inactivation of monoamine neurotransmitters in the brain, including pretty much every chemical you’ve heard associated with depression (serotonin, melatonin, dopamine, norepinephrine, etc.). Thus, it’s when the oxidation-inactivation-reabsorption mechanism goes haywire that depression is likely to occur. In this context, it also becomes easier to understand the class of antidepressant drugs known as monoamine oxidase inhibitors (MAOIs). For an easy-to-read but more thorough explanation of this biology, we recommend this resource.

Neurogenesis: Once thought impossible, neurogenesis refers to the creation and distribution of new neurons in the brain. New evidence instead suggests that the hippocampus benefits from neurogenesis and that this disruption is part of many depressive disorders. In depressed individuals, the hippocampus may actually shrink about 10 percent. It’s also worth pointing out that this lack of neurogenesis may not be the primary cause of depression, but rather a sign of the toll that depression can take over time. The relative level of neurogenesis has also been offered as a partial explanation of why some people but not others respond to antidepressants. More information about the connection between neurogenesis and depression can be found here.

Hereditary & Genetic Causes: There is a strong link between genetic factors and depressive disorders. Most studies suggest heritability is 40-50 percent, lending credence to the notion that—while individual cases may skew heavily toward either hereditary or social causes—depression overall has roughly equal parts of nature and nurture. Aside from the fact that we’re pretty sure depression isn’t a single-gene disorder, we know little about the combination of genes that may contribute to a higher risk profile.

Infectious Disease: One of the potential causes of depression is infectious disease. The evidence put forth by this researcher includes inflammatory biomarkers in those with depression, the propensity for infectious agents to affect key systems of the brain, and immuno-hereditary factors.