What Causes Depression?

Depression is a complex disease. No one knows exactly what causes it, but it can happen for a variety of reasons. Some people have depression during a serious medical illness. Others may have depression with life changes such as a move or the death of a loved one. Still others have a family history of depression. Those who do may have depression and feel overwhelmed with sadness and loneliness for no known reason.

Lots of things can increase the chance of depression, including the following:

• Physical, sexual, or emotional abuse can make you more vulnerable to depression later in life.
• 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.
• Some drugs, such as isotretinoin (used to treat acne), the antiviral drug interferon-alpha, and corticosteroids, can increase your risk of depression.
• Depression in someone who has the biological vulnerability to it may result from personal conflicts or disputes with family members or friends.
• Sadness or grief after the death or loss of a loved one, though natural, can increase the risk of depression.
• While sex is not a cause, 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.
• A family history of depression may increase the risk. It’s thought that depression is a complex trait, meaning there are probably many different genes that each exert small effects, rather than a single gene that contributes to disease risk. The genetics of depression, like most psychiatric disorders, are not as simple or straightforward as in purely genetic diseases such as Huntington’s chorea or cystic fibrosis.
• 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.
• 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.
• Sometimes, depression happens along with a major illness or may be triggered by another medical condition.
• 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.

We know that depression can sometimes run in families. This suggests that there’s at least a partial genetic link to depression. Children, siblings, and parents of people with severe depression are somewhat more likely to have depression than are members of the general population. Multiple genes interacting with one another in special ways probably contribute to the various types of “inherited” depression. Yet despite the evidence of a family link to depression, it is unlikely that there is a single “depression” gene, but rather, many genes that each contribute small effects toward depression when they interact with the environment.

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
• 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
• Certain medications, such as some high blood pressure medications or sleeping pills (talk to your doctor before stopping any medication)

Depression is not a normal part of growing older, and it should never be taken lightly. Unfortunately, depression often goes undiagnosed and untreated in older adults, and they may feel reluctant to seek help. Symptoms of depression may be different or less obvious in older adults, such as:

• Memory difficulties or personality changes
• Physical aches or pain
• Fatigue, loss of appetite, sleep problems or loss of interest in sex — not caused by a medical condition or medication
• Often wanting to stay at home, rather than going out to socialize or doing new things
• Suicidal thinking or feelings, especially in older men

Sources: Mayo Clinic, Web MD, Harvard Medical School