What Causes Depression?
Bob’s article describing his experience with depression has received more than the usual amount of attention. So, my interest that much greater when, while reading “Science News” I came across the feature “Sick and Down” about one of the causes of depression.
The story discusses a link between the immune system and depression. Part of the biology of depression is reduced levels of serotonin in the brain. It seems that cytokines, an inflammitory protein produced by the immune system to fight infection, can cause this reduction. It is reasoned that this is an evolutionary response to illness that is built into all mammals. The advantage is a conservation of energy that aids the battle against the infection.
However, when inflammation is prolonged, or caused by stress (or diet?), sickness behavior can turn into depression. Chronic illnesses such as MS, diabetes and cancer can lead to depression. A new diagnostic category: “Major Depressive Disorder with Increased Inflammation” has been considered.
In addition to inflammation, certain drugs that increase immune response have been found to cause depression. These include some drugs used in chemotherapy and for treating hepatitis C. Other drugs that block cytokines seem to improve mood.