What Causes Depression?

Depression is a mental health condition classified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Symptoms of depression include persistent feelings of sadness, loss of interest in previously enjoyed activities, changes in appetite and sleep patterns, difficulty concentrating, feelings of worthlessness, and, in severe cases, thoughts of self harm or suicide. 

If you are experiencing suicidal thoughts or urges, call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255) or text 988 to talk to someone over SMS. Support is available 24/7.

Depression affects approximately 5% of the global population, as stated by the World Health Organization. This complex condition encompasses several depression disorders, including major depressive disorder and bipolar disorder, producing widely varying symptoms. The accurate diagnosis of depression is challenging due to its complexity, and a unified theory explaining the exact cause of depression is yet to be established.

Potential causes of depression

For several decades, researchers believed that an imbalance of brain chemicals, specifically nerve cells, was the primary contributing factor for what caused depression. However, recent studies, supported by organizations like the American Psychiatric Association, suggest that such an imbalance may not be the cause of depression. Instead, science now points to a confluence of causes that may be at work in depression disorders. Elements like brain structure, genetics, hormonal changes, family history, certain personality traits, existing mental health conditions, and environmental factors, including stressful life events, have all been linked to depression through scientific research. 

Chemical imbalance

In the 1960s, researchers discovered a connection between low levels of serotonin—a brain chemical that helps with a number of important processes in the body—and symptoms of clinical depression. Diagnosing depression based on the presence of chemical imbalances became the prevailing theory. Recently, however, researchers and institutions like the National Institute of Mental Health have questioned whether this is the true cause of depression. One broad-based study on the chemical imbalance theory concluded that its legitimacy is not supported by the available evidence. While still considered a contributing factor by many, science now points to a combination of other causes (brain structure, genetics, stressful events, etc.) as a more likely basis for the development of depression. 

Brain structure

The brain is responsible for managing our mood, so it makes sense that changes in its function and composition can lead to symptoms of depression. This was partly why researchers formulated the chemical imbalance theory and developed medication like selective serotonin reuptake inhibitors (SSRIs) to address it. The idea was that antidepressants would correct that imbalance in the brain and improve low mood, and there is research that supports the efficacy of antidepressants in treating depression.

So, if antidepressants that boost production of brain chemicals like serotonin have been proven to work for depression, then why is a chemical imbalance no longer the dominant theory to diagnose depression? Researchers have found that these antidepressants may help increase neuron production, which in turn can decrease symptoms of depression. This suggests that brain structure and neuron activity may be more important than the volume of chemicals. 

The connection between brain structure and depression is supported by research linking depression to a small hippocampus and reduced neuron creation. Studies also show that treatment for depression, including addressing depression risk factors and health problems, can change the formation of the brain.

Genetics

Researchers have found a significant link between certain genes and depressive disorders. In fact, some in the medical community believe genetics can account for up to half of the total cause of depression. A genetic connection to depression is evident in the fact that identical twins—who have the exact same genetic makeup—experience symptoms of depression at a higher rate than non-identical twins. 

The exact genes that are linked to depression can vary, though. Studies have found a connection between the chromosome 3p25-26 and major depression. There is also evidence that the gene HTR2A can make individuals experiencing depression more likely to respond positively to antidepressants. Further complicating things is the fact that people with depression typically have several different genes that may affect the development of a depression disorder.

Genetics can play a part in depression by affecting brain structure and function. There is also evidence that personality traits that arise out of certain genes may lead to a greater likelihood of developing depression. For example, when a person has a specific variant of the 5-HTT gene, they may be more likely to experience a depressive disorder after situational depression. 

Environmental factors

Coping mechanisms for stress can be helpful in managing the environmental causes of depression, which can include the actual environment—air quality, noise pollution, natural disasters—but more commonly include concerns like trauma, chronic pain, disease, stress, and grief. Chronic illness, such as heart disease or diabetes, is one of the most common contributors to depression. A loss in the family or relationship conflict can also lead to symptoms of depression. 

Depression has been strongly linked to high levels of cortisol, which is the stress hormone. This suggests that experiencing chronic stress can increase your chances of developing depression symptoms. Additionally, trauma early in life can not only lead to depression but can also affect how well individuals respond to depression treatments. 

The physical space you live in can also be an important factor to pay attention to. One study found that an individual’s housing situation can have a significant impact regarding symptoms of depression. There is also research pointing to links between those who experience depression and lack of green spaces, loud environments, and poor air quality.

Hormonal changes

In addition to the above causes, depression can be brought on by hormonal shifts caused by various biological changes, such as:

• Puberty 
• Premenstrual syndrome and premenstrual dysphoric disorder
• Pregnancy
• Postpartum depression
• Perimenopause and menopause

Additional health concerns that can create hormonal fluctuations and subsequent depression symptoms include:

• Deficiency in testosterone estrogen, or progesterone
• Hyperthyroidism or hypothyroidism
• Adrenal issues involving cortisol and adrenaline

Because of these links, researchers have found evidence that sex hormone supplementation may be a valid method of treatment for depression disorders like postpartum depression and premenstrual depression. 

Lifestyle

The way we live our life can have a significant impact on the severity of depression symptoms and may be, partially, a cause for the disorder. In addition to the above sources of depression, diet, sleep quality, alcohol consumption, smoking, recreational drugs, and excessive screen usage can affect our mood. One study found that sleep, diet, and screen time, in particular, can exacerbate symptoms of depression. Another study from the Centers for Disease Control found a link between smoking and increased instances of mental disorders like depression.

In a wide-ranging study on the link between alcohol use disorder and major depression, researchers found a bi-directional relationship between the two mental health conditions. The study found that those who live with alcohol use disorder are twice as likely to also experience major depression, and vice versa. 

Modern life can present many concerns that may contribute to depression. There is evidence that having too many choices—a side effect of our ability to get so many different things at once—can lead to mental health challenges like stress and depression. Trouble making decisions could cause a loss of interest or similar depression symptoms.

Social media is another modern contributor to major depressive disorder. A study in the Journal of Social and Clinical Psychology found that using social media platforms like Facebook can cause symptoms of depression. Social media can prompt some users to compare their lives to those of their peers, which might seem more alluring than they actually are due to other users’ propensity to tell primarily exciting and fun milestones, events, or other moments. The act of comparison may exacerbate depression symptoms.

Counseling and treatment options for you

An increasingly large number of studies show that online therapy can be a useful method of treatment for symptoms of depression that may arise from various sources. In a study on the effectiveness of online cognitive behavioral therapy (CBT) for depression, researchers found that treatment could significantly improve depression symptoms. Participants reported that these improvements in depression were sustained at both 9- and 12-month follow-ups. Cognitive behavioral therapy is a widely accepted modality that helps people replace negative thought patterns, such as those that may exacerbate or lead to symptoms of depression. 

If you’d like help learning more about the sources of depression, your specific symptoms, or similar concerns, consider utilizing an online mental health platform like BetterHelp. BetterHelp allows you to connect with a licensed mental health professional remotely. If you're struggling to leave the house due to a medical condition, like depression, or aren't comfortable meeting with a therapist face to face, you can participate in therapy through video call, voice call, or in-app messaging. BetterHelp is also an affordable option. Signing up starts at $65 to $100 per week (based on factors such as your location, referral source, preferences, therapist availability and any applicable discounts or promotions that might apply), and you can cancel anytime. A licensed therapist experienced in depression can provide you with the support and guidance you deserve as you work to understand possible sources of depression and improve your depression symptoms.