It’s not known exactly what causes depression. As with many mental disorders, a variety of factors may be involved, such as:
- Biological differences. People with depression appear to have physical changes in their brains. The significance of these changes is still uncertain, but may eventually help pinpoint causes.
- Brain chemistry. Neurotransmitters are naturally occurring brain chemicals that likely play a role in depression. Recent research indicates that changes in the function and effect of these neurotransmitters and how they interact with neurocircuits involved in maintaining mood stability may play a significant role in depression and its treatment.
- Hormones. Changes in the body’s balance of hormones may be involved in causing or triggering depression. Hormone changes can result with pregnancy and during the weeks or months after delivery (postpartum) and from thyroid problems, menopause or a number of other conditions.
- Inherited traits. Depression is more common in people whose blood relatives also have this condition. Researchers are trying to find genes that may be involved in causing depression.
Risk factors
Depression often begins in the teens, 20s or 30s, but it can happen at any age. More women than men are diagnosed with depression, but this may be due in part because women are more likely to seek treatment. Factors that seem to increase the risk of developing or triggering depression include:
- Certain personality traits, such as low self-esteem and being too dependent, self-critical or pessimistic
- Traumatic or stressful events, such as physical or sexual abuse, the death or loss of a loved one, a difficult relationship, or financial problems
- Age. People who are elderly are at higher risk of depression. That can be made worse by other factors, such as living alone and having a lack of social support.
- Certain medications. Some drugs, such as isotretinoin (used to treat acne), the antiviral drug interferon-alpha, and corticosteroids, can increase your risk of depression.
- Vitamin D deficiency. Studies have linked depressive symptoms to low levels of vitamin D.
- Conflict. Depression in someone who has the biological vulnerability to it may result from personal conflicts or disputes with family members or friends.
- Gender. Women are about twice as likely as men to become depressed. No one’s sure why. The hormonal changes that women go through at different times of their lives may play a role.
- Major events. Even good events such as starting a new job, graduating, or getting married can lead to depression. So can moving, losing a job or income, getting divorced, or retiring. However, the syndrome of clinical depression is never just a “normal” response to stressful life events.
- Other personal problems. Problems such as social isolation due to other mental illnesses or being cast out of a family or social group can contribute to the risk of developing clinical depression.
- Serious illnesses. Sometimes, depression happens along with a major illness or may be triggered by another medical condition.
- Substance misuse. Nearly 30% of people with substance misuse problems also have major or clinical depression. Even if drugs or alcohol temporarily make you feel better, they ultimately will aggravate depression.
- Blood relatives with a history of depression, bipolar disorder, alcoholism or suicide
- Being lesbian, gay, bisexual or transgender, or having variations in the development of genital organs that aren’t clearly male or female (intersex) in an unsupportive situation
- History of other mental health disorders, such as anxiety disorder, eating disorders or post-traumatic stress disorder
- Abuse of alcohol or recreational drugs
- Serious or chronic illness, including cancer, stroke, chronic pain or heart disease