Depression - Biological factors

==Biological causes
 * Heredity - The tendency to develop depression may be inherited; there is some evidence that this disorder may run in families. A 2004 press release from the National Institute of Mental Health declares "major depression is thought to be 40-70 percent heritable, but likely involves an interaction of several genes with environmental events."




 * Neurochemical There may be changes or imbalances in chemicals that transmit information in the brain, called neurotransmitters. Many modern antidepressant drugs attempt to increase levels of certain neurotransmitters, such as serotonin and norepinephrine.  Although the causal relationship is unclear, it is known that antidepressant medications can relieve certain symptoms of depression, although critics point out that the relationship between serotonin, SSRIs, and depression usually is typically greatly oversimplified when presented to the public (see here).

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 * Neuroanatomy Recent research has suggested that there may be a link between depression and neurogenesis of the hippocampus.

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 * Hormonal factorsThe levels of hormones, the chemical messengers in the body that help regulate metabolism, have been linked to depression

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 * Postpartum depression (also known as postnatal depression) – Dr. Ruta M Nonacs writes that while many women experience some mood changes after giving birth, "10-15% of women experience a more disabling and persistent form of mood disturbance (eg, postpartum depression, postpartum psychosis)." When it occurs, the onset typically is within three months after delivery, and it may last for several months.  About two new mothers out of a thousand experience the more serious depressive disorder Postnatal Psychosis which includes hallucinations and/or delusions.


 * Medical conditions – Certain illnesses, including cardiovascular disease, hepatitis, mononucleosis, hypothyroidism, and organic brain damage caused by degenerative conditions such as Parkinson disease or by traumatic blunt force injury may contribute to depression, as may certain prescription drugs such as birth control pills and steroids. Gender dysphoria can also cause depression.

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 * Nutrition – The increase in depression in industrialised societies has been linked to diet, particularly to reduced levels of omega-3 fatty acids in intensively farmed food and processed foods . This link has been at least partly validated by studies using dietary supplements in schools and by a double-blind test in a prison. An excess of omega-6 fatty acids in the diet was shown to cause depression in rats.

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 * Alcohol and other drugs – Alcohol can have a negative effect on mood, and misuse of alcohol, benzodiazepine-based tranquilizers, and sleeping medications can all play a major role in the length and severity of depression. The link between frequent cannabis use and depression is also widely documented, although the direction of causality remains in question; Dr. Salynn Boyles writes, "...research has linked pot smoking with depression and schizophrenia ... daily use [of marijuana] was associated with a five-fold increase in later depression and anxiety among young women. But depression and anxiety were not predictive of later marijuana use."

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