Is depression genetic or environmental?

Depression is a common mental health condition with several potential causes and contributing risk factors, including genetic and environmental factors. Depression is often caused by a combination of factors which may differ from person to person.

Is depression genetic?

There is a great deal of research into the causes and contributing risk factors of depression, with one specific focus being on the genetic factors associated with depression. Several studies have been conducted to try and ascertain the level of genetic heritability of depression.

Some of these studies involve identical (monozygotic) twins, who share 100% of the same genes, so it is presumed that if both twins develop depression, then it is likely to be genetic. Results from these studies suggest that a genetic factor can be identified in around half of those with clinical depression ^[1][2].

Similarly, studies have found that many people with depression have a parent with depression, further implying a genetic predisposition. It is believed that an individual with a family history of depression is 2-3 times more likely to develop the condition. This risk increases if the family history includes more severe and reoccurring episodes of depression ^[2][3].

Scientists believe that there are multiple genes responsible for this genetic factor, some of which may alter levels and functioning of chemicals in the brain that can influence the risk of depression, although this is currently unclear and requires further research ^[2][4][5].

Furthermore, research indicates that certain personality traits can increase the risk of developing depression, such as neuroticism, which can be a genetic trait ^[6].

Similarly, is thought that resilience is related to genetic factors, and people who lack resilience are more likely to develop depression in response to stress and trauma, indicating that it is possible to inherit a vulnerability to developing depression following adverse events ^[4].

Many people with depression have no relatives with the condition, so although there is certainly a genetic component to the development of the condition, this is not the only contributing factor ^[5].

Can depression be caused by environmental factors?

Environmental factors are the nongenetic factors that can influence the risk of developing depression. This is often related to events in childhood, current life stressors, and social support.

Childhood trauma, such as abuse, neglect, or bullying, has been found to be significantly linked to the development of depression in adulthood. It is believed that stress caused by trauma impacts brain development, in addition to causing ongoing emotional distress ^[2][4][7].

Research shows that those who have been abused in childhood are around four times more likely to go on to develop depression than those with no history of childhood abuse. Similarly, it is believed that childhood abuse also increases the severity and reoccurrence of depression, while negatively impacting recovery rates ^[2][4].

However, there are many people who experience childhood trauma who do not develop depression, which is believed to be influenced by social support, parental relationships, personality types, and the time and duration of abuse. These influences may contribute to higher levels of resilience, thereby preventing depression, so resilience could be both genetic and environmental ^[4].

Similarly, while a family history of depression may indicate a genetic risk, it may also be that children living with a family member who has depression are exposed to certain attitudes and behaviors that influence their own mood, behavior, and personality. For example, a neurotic parent may lead to a neurotic offspring, a trait that may be both genetically inherited and a learned behavior ^[6][8].

Furthermore, life stressors in adulthood can contribute to an increased risk of the development of depression. These stressors can include the death of a loved one, the breakdown of a relationship, and housing, employment, or financial issues ^[8][9].

Research has also found that social isolation is a significant risk factor in the development of depression at all ages, from adolescence to old age ^[10].

Other risk factors for depression

Aside from genetic and environmental factors, there are several other factors that can increase the risk of developing depression, which are all likely to be impacted by genetic and environmental contributions ^[3].

Brain function

Studies show that neurobiology has an impact on the development of depression, such as a chemical imbalance caused by altered levels and activity of neurotransmitters, including serotonin, dopamine, and norepinephrine ^[4][11].

Additionally, it is believed that depression may be related to abnormal activity in areas of the brain such as the amygdala, impacting emotional regulation and reward-processing ^[2][11].

Research also indicates that many people with depression have a smaller hippocampus. This is believed to be because of a reduced production of nerve cells due to stress and trauma, which then impacts communication between cells in the brain, causing or exacerbating symptoms of depression ^[4][11].

Hormones

During the menstrual cycle, menopause, and pregnancy, and after childbirth, significant hormonal fluctuations occur which can contribute to the development of symptoms or episodes of depression ^[9][12].

Other mental health issues

Many people with depressive disorders also experience other mental health conditions, including posttraumatic stress disorder (PTSD), obsessive-compulsive disorder (OCD), eating disorders, and anxiety disorders. This suggests that some people may be at a higher risk of developing mental illness, or that other conditions also contribute to the development of depression ^[8].

Medication, drugs, and alcohol

Many medications, for both mental and physical health, can contribute to or cause symptoms of depression. Similarly, illicit substances and alcohol can also increase the risk of developing depression, as well as potentially worsening general physical and mental wellbeing ^[8][9].

Physical health

Depression is often linked to various physical health conditions. Some illnesses can cause symptoms similar to those that occur with depression, as well as causing depressive symptoms due to stress relating to ongoing or severe conditions and treatments, and chronic pain ^[8][9].

How to avoid inheriting depression

There are several ways to improve and maintain your physical and mental wellbeing, to help prevent depression or to reduce the impact of depression symptoms. This includes ^[9][10][13]:

• Eating a healthy diet: Studies show that mental health can be impacted by the food we eat, just as much as our physical health. Processed food and foods high in sugar can increase the risk of developing symptoms of depression, while foods that are high in vitamins and minerals can help to prevent low mood and anxiety.
• Good sleep hygiene: Getting plenty of sleep, going to bed and waking up at the same time each day, and avoiding screens before bedtime can all help improve quality of sleep, which has a significant impact on mental and physical health.
• Exercising: Engaging in regular exercise is also important for physical and mental wellbeing and can help to reduce or prevent symptoms of depression.
• Mindfulness: Mindfulness techniques, including yoga and meditation, have been found to be beneficial in preventing or reducing feelings of stress, depression, and anxiety.
• Talking to others: It is important to talk to someone if you ever experience feelings of low mood or depression, whether a professional, friend, or family member, as this can help to prevent worsening mental health.