What Causes Depression?

Depression, also known as major depressive disorder, is often associated with intense sadness, lack of energy, low mood, and loss of interest. These symptoms can manifest in mild or severe ways. However, the causes of depression aren’t fully understood, even though it's one of the most common mental health conditions. Experts believe there could be several factors, including genetics, stress, and health conditions. 

The American Psychiatric Association estimates one in six U.S. adults experience depression in their lifetime. But a person’s experience with depression — and the underlying cause — is very individual. If you think you're prone to depression or have depressive symptoms, understanding your depression risk can help you take steps to find support and treatment. 

Let’s look at some potential depression causes and triggers. Plus, how and when to seek help. 

Brain Chemistry

Your brain has chemicals, known as neurotransmitters, that tell your body how to function. If the neurotransmitters dopamine or serotonin (both feel-good hormones) are too high or too low, your mood may be affected. Researchers theorize that since dopamine helps you feel motivated and rewarded, any dopamine dysfunction may lead to depressive symptoms like loss of interest and motivation. What causes this imbalance varies, but researchers think trauma and stress may trigger dopamine issues.  

The link between depression and serotonin is even less understood. Low serotonin levels don’t appear to cause depression, but serotonin helps you process emotions that affect your mood. Increasing serotonin levels can also be an effective way to treat depression. For that reason, depression is commonly treated with medications that impact these brain chemicals, such as selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs).

Genetics

People with family members who have or had depression are more likely to develop depression. Having had depression yourself at one point also increases your risk for depression later in life.

Research also suggests people with depression may have genetic variants that predispose them to the condition. While not completely proven, these variants may cause changes in brain chemistry related to depression.

Thyroid Disorders

If you have depression symptoms, your healthcare provider may check that your thyroid is functioning properly. This gland in your neck creates essential hormones that affect many functions in your body and nervous system, including your mood.

Hypothyroidism — a condition where you produce low levels of thyroid hormones — has been linked to depression symptoms. Other underactive thyroid symptoms include fatigue, joint and muscle pain, cold sensitivity, and dry skin or hair. If hypothyroidism is to blame for your depression, medications that help replace hormones can help manage the condition. 

Nutritional Deficiencies

While an imbalanced diet can affect anyone's mood, research shows people with depression often have deficiencies in omega-3 fatty acids, B vitamins, magnesium, and zinc. These nutrients all help create or aid neurotransmitters necessary for healthy brain function. But exactly how diet can lead to depression isn’t proven. 

For example, Omega-3 fatty acids help your brain process emotional behavior and aid serotonin neurotransmission needed to regulate your mood. Research also shows supplementing omega-3 fatty acids can help treat some cases of depression.

Menstruation

People who get periods may experience a form of depression called premenstrual dysphoric disorder (PMDD). The condition causes severe premenstrual syndrome (PMS) symptoms and low mood a week or two before your period. PMDD can also cause physical symptoms like cramps, bloating, breast tenderness, and headaches.

You’re more likely to deal with PMDD if you already have anxiety or depression. Hormonal shifts during your menstrual cycle may also disrupt serotonin levels and make you feel depressed. If you are diagnosed with PMDD, your healthcare provider may suggest treatments like therapy, hormonal birth control, or antidepressants.

Pregnancy

Pregnancy causes hormonal shifts, stress, and emotional and physical demands that may lead to depression. Known medically as perinatal depression, you can experience this type of depression during pregnancy (prenatal depression) and after childbirth (postpartum depression). Genetics may also increase your risk of perinatal depression. 

Depression can make caring for yourself and others difficult, but treatment with medication, therapy, or a combination of both, can often make you feel better. 

Seasonal Changes

Seasonal changes during the darker fall and winter months may lead to a type of depression called seasonal affective disorder (SAD). This is because lack of sunlight exposure can alter your body's circadian rhythm, which regulates hormones and other body functions related to mood. 

Light therapy is often used to help treat SAD, and depression symptoms typically improve in the spring and summer.

Depression Risk Factors

Certain life experiences and environmental factors can also increase your risk of developing depression, especially if you’re already at risk due to other health or genetic factors. These risk factors don’t necessarily cause depression, but they can trigger depression in some people.  

Adverse Childhood Experiences

Childhood plays an important role in developing your brain and personality. Research shows severe early childhood stress, such as abuse, can fundamentally change brain function and lead to severe depression later in life.

Substance Use Disorders

Having an alcohol use disorder and depression are often linked. Some people may also self-medicate their low mood by drinking, which makes the problem worse. Alcohol is technically considered a depressant that slows body functions, including how your body balances feel-good brain chemicals. Drinking more alcohol increases your risk of developing depression. 

People who smoke cigarettes are also more likely to become depressed, but the exact reason is unknown.

Medications

Some prescription medications can increase the risk of depression by altering levels of neurotransmitters that help regulate mood. For example, medications that treat seizure disorders, Parkinson's disease, migraine, and cardiovascular problems may result in depression symptoms. Some antibiotics and antifungal drugs can also lead to a depressed mood.

Talk to your healthcare provider if you take medication and think it may be impacting your mood.

Sleep Deprivation

One common symptom of depression is sleep changes, which can include trouble sleeping. But there's also evidence that sleep deprivation and insomnia can increase your risk of depression.

A bad night's sleep can zap your mood, and a long-term lack of sleep can also affect mental health. Research shows that non-depressed folks with insomnia are more likely to develop depression than those who get enough sleep.

Stress

Stressful life circumstances like major transitions, breakups, grief, and loss can impact mood. Being part of a marginalized community can also contribute to depression, as can isolation. Experiencing a chronic illness, especially in later adulthood, is also linked to a higher risk of developing depression.

Depression may stem from negative thinking patterns related to stressful situations. Psychotherapy can help people think differently about difficult circumstances and, as a result, improve depression symptoms.

A Quick Review

Several genetic, health, and environmental factors related to brain chemicals and hormones may cause depression. If you think you may have depression, speaking with your healthcare provider is a good place to start. Seeing a therapist or other mental health provider can also help. 

If you constantly feel sad and hopeless, and these feelings start to interfere with your daily activities, it's time to seek help. It can feel vulnerable to admit you're struggling and ask for help, but there are several effective treatments that can help improve your quality of life.