There are a variety of causes of depression. While researchers have established that hereditary, social, and environmental factors can influence a person’s risk for depression, for the most part, they don’t know why some people suffer from depression and some do not.
Different types of depression are associated with different causes and risk factors, but the exact combination of factors will vary for each person. It is usually a combination of personal factors and recent events, not just one event, that leads to depression.
Risk factors for depression
It is important to note that while science is good at finding correlation – apparent relationships – between risk factors and depression, correlation does not prove that the factor causes depression. Many risk factors for depression have been identified and are being studied, but none have been pinpointed as the singular cause of depression.
About 7 percent of the U.S. population will experience depression each year. Approximately one in six people will have a depressive episode at some point in their life. The factors below can increase this risk.
People who have a at least one close relative (parent or sibling) with depression or bipolar disorder have a greater risk of developing depression themselves. However, life events and personal circumstances also help to determine your risk for depression. Having a relative with depression does not automatically mean you will, too.
Stress and trauma
Most people experience difficult life events, be it the death of a loved one, divorce, job loss, car accidents, violence, or serious illness. Stressful situations will not result in a mood disorder for most people, but for some, stress is a key risk factor for depression.
Children who experience the loss of a parent or are neglected or abused are more likely to experience depression as adults. Scientists believe that childhood trauma may cause changes in the brain at a chemical level. More research is needed to determine the exact relationship between psychological trauma, changes in the brain, and depression.
About 30 percent of people who abuse drugs or alcohol also have depression. Some may be self-medicating their preexisting depression, while in others, the substance itself causes the depression. Since alcohol is known to be a depressant, people who have both depression and substance abuse often need to receive integrated treatment for both conditions simultaneously.
Illness and medications
It is thought that in 10 to 15 percent of people with depression, depressive symptoms are caused by an illness or medication. Some medical conditions are known to be direct causes of depression. Thyroid imbalances can trigger manic or depressive behaviors, depending on whether thyroid hormone levels are too high or too low. Additionally, many chronic conditions such as lupus, Parkinson’s, HIV, and multiple sclerosis have been associated with mood disorders. Severe head injury can also cause changes in the brain that trigger depression, emotional problems, and mood swings.
Certain medications, such as blood pressure medications and steroids, can set off depressive episodes. Not everyone taking these drugs will experience depression, but if you are taking a medication that has a negative impact on your mood, tell your doctor as soon as possible. They can determine whether the dosage or medication needs to change, or if two medications are causing a negative interaction.
People who have anxiety or low self-esteem, who are perfectionists, or who are deeply self-critical are at greater risk for depression. These traits may be inherited, the result of childhood experiences, or both.
People who suddenly find themselves cut off from family and friends are at an increased risk for depression.
Due to hormonal and physical changes, new mothers may experience postpartum depression in the weeks and months following childbirth. Like all other forms of depression, postpartum depression is not a character flaw or a sign a mother does not love her baby, but a serious mental illness that can be treated. While the exact cause of postpartum depression isn’t known, financial or marital stress, complications during pregnancy or in birth or breastfeeding, and insufficient support in tending to the baby are all recognized risk factors.
Seasonal affective disorder (SAD) is associated with a lack of sunlight during the fall and winter months. Some researchers believe that in people with SAD, lack of sunlight causes dysfunction in part of the brain called the hypothalamus. SAD may lead to an overproduction of melatonin (a hormone that makes you feel sleepy) or an underproduction of serotonin (a hormone responsible for sleep, appetite, and mood). Low levels of sunlight may also disturb the body’s circadian rhythm, the internal clock that helps to regulate the sleep/wake cycle.