Major depression afflicts 6.7 percent of American adults each year, according to the National Institute of Mental Health. Whether depression manifests with symptoms severe enough to be a diagnosable disorder, or occurs just as the result of life events, the tendency of an individual to feel depressed has biological underpinnings. Scientists are investigating at least three different biological arenas: genetics, neurotransmitters in the brain, and hormonal influences.
Genetics and Family History
Some forms of depression are passed down from generation to generation through the genetic code. However, genetics does not bear 100 percent of the responsibility for the development of major depression. Research studies of identical twins have generally established that genetics seems to account for about 29 to 42 percent of risk for depression, in which genetic causality is higher for women, according to a 2006 study in the "American Journal of Psychiatry."
Scientists have identified specific genes in human DNA that appear to be directly responsible for the level of risk for depression. Specifically, genes that control the levels of certain neurotransmitters in the brain, such as serotonin, are implicated, according to a 2006 article on the Science Daily website.
Neurotransmitters
Neurotransmitters are chemical messengers, sending signals throughout the nervous system that help regulate mood and behavior. Scientists have known for a long time that modifications of some of these neurotransmitters can affect mood. Several antidepressant medications have been developed that target specific neurotransmitters to alleviate depression.
Three neurotransmitters of particular interest are serotonin, norepinephrine (also known as noradrenalin) and dopamine. Increasing the amount of these neurotransmitters available through the brain seems to alleviate mood in many patients, according to the Brain Explorer website. Antidepressants that target these neurotransmitters include tricyclic antidepressants, or TCAS, such as amitriptyline (Elavil), selective serotonin reuptake inhibitors, or SSRIs, such as fluoxetine (Prozac) and dopamine-norepinephrine reuptake inhibitors, or DNRIs, such as bupropion (Wellbutrin).
Hormones
Several hormones can affect mood, particularly in women. Fluctuations in hormones can lead to feelings of depression during certain times of the month, according to the Women's Health website. If severe, such depression symptom can be diagnosed as premenstrual dysphoric disorder, or PMDD. After childbirth, a woman experiences a sudden drop in estrogen and progesterone, which can also lead to feelings of the "baby blues," which occur in 40 to 85 percent of women, or even more severe postpartum depression, which occurs in 10 to 15 percent of new mothers, according to the ObGyn website. The change in hormones that accompany menopause can also lead to feelings of depression, according to Consumer Reports Health website.
References
- National Institute of Mental Health: The Numbers Count: Mental Disorders in America
- "American Journal of Psychiatry"; A Swedish National Twin Study of Lifetime Major Depression; K.S. Kendler and colleagues; Jan 2006
- Science Daily: Scientists, Linking Gene with Serotonin And Depression, Offer Insights To New Treatments
- Brain Explorer: Depression Aetiology
- Consumer Reports Health: Depression in Adults: Essentials
