Depressed feelings can result from many different causes. Major depressive disorder manifests as feelings of sadness or loss of interest along with related symptoms such as insomnia, loss of appetite and fatigue, according to the American Psychiatric Association. However, feelings of depression do not always constitute a diagnosable disorder and can happen to anyone.
Depression can occur because of genetic predisposition, environmental factors and certain medical conditions.
Genetics and Family History
Scientists have linked major depression to genetic factors. They study the genetics of depression through identical twin studies. Identical twins share 100% of their genetic makeup; therefore, if scientists find that depression co-occurs in identical twins more than in non-identical twins, genetics is responsible. Through these studies, researchers have found that genetics can account for up to 42% of depression in women and about 29% of depression in men, according to a study published in a 2006 issue of the "American Journal of Psychiatry."
Scientists have also identified specific genes that affect the occurrence of depression, particularly genes that control the production of neurotransmitters in the brain, according to a 2006 article on the Science Daily website.
Environment and Life Events
In addition to genetic factors, the environment in which a person lives contributes greatly to the occurrence of depression. Environmental factors include anything we encounter in our everyday lives, such as chronic stress resulting from work or family problems, or traumatic events such as a life-threatening accident or the death of a loved one. These experiences, and more specifically, our interpretation of them, can affect our mood, according to the All About Depression website.
Although any individual can become temporarily depressed because of a negative life situation, only some individuals will experience the protracted experience of depression that is diagnosable as major depression. The environment appears to interact with genetic factors to influence who will experience a major depression, according to a 2003 article in "Science" magazine.
Medical Conditions
Several medical conditions can present with depression as a symptom. The most notable of these in the elderly population is dementia. Alzheimer's disease can present with depression symptoms in certain stages of the disease as it progresses. Researchers estimate that up to 40% of individuals with Alzheimer's also experience significant depression, according to the Alzheimer's Association website.
Chronic illness or pain can also lead to depression. Pain and depression are closely linked because the pathways that send pain signals are the same as those that regulate mood, according to the Harvard Health Letter website. Therefore, individuals with pain have an increased risk of also experiencing depression, and vice versa. Other chronic illnesses can also lead to feelings of depression because of the change in life situation and challenges of disability.
References
- "Diagnostic and Statistical Manual of Mental Disorders"; American Psychiatric Association; 2000.
- "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
- All About Depression: Environmental Causes of Depression
- "Science"; Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT gene; A. Caspi and colleagues; vol 301, 2003
