In a recent study published in the journal Nature Mental Health, an international team of researchers including the University of Cambridge and Fudan University looked at a combination of lifestyle factors, genetics, brain structure, and our immune and metabolic systems to identify potential mechanisms that might explain this link.
New findings suggest that maintaining a healthy lifestyle that includes moderate drinking, a healthy diet, regular physical activity, healthy sleep and frequent social activities, while avoiding smoking and excessive inactivity, can reduce the risk of depression.
According to the World Health Organization, approximately one in 20 adults suffers from depression, and the disease poses a huge burden to global public health. The factors that influence the onset of depression are very complex, including biological factors and lifestyle factors.
Data sources and key findings
To better understand the relationship between these factors and depression, researchers turned to the UK Biobank, a biomedical database and research resource that contains anonymized genetic, lifestyle and health information about participants.
By following data from nearly 290,000 people, 13,000 of whom suffered from depression, for nine years, the team identified seven healthy lifestyle factors associated with a reduced risk of depression. These factors are:
Drink in moderation
healthy eating
exercise regularly
healthy sleep
no smoking
Try not to sit still for too long
Participate in social activities regularly
Of all these factors, getting good sleep - between seven and nine hours a night - was the most influential, reducing the risk of depression (both single depressive episode and drug-resistant depression) by 22 percent.
Regular interaction with others can reduce the overall risk of depression by 18% and is the most effective way to prevent the recurrence of depression.
Moderate drinking can reduce the risk of depression by 11%, eating a healthy diet can reduce it by 6%, participating in regular physical exercise can reduce it by 14%, never smoking can reduce it by 20%, and sitting for moderate to low periods can reduce it by 13%.
Based on the number of healthy lifestyle factors individuals adhere to, they are assigned to one of three groups: adverse, moderate, and favorable lifestyle groups. Compared with people in the unfavorable lifestyle group, those in the moderate lifestyle group were about 41% less likely to suffer from depression, while those in the favorable lifestyle group were 57% less likely to suffer from depression.
Genetics and lifestyle
The team then examined the participants' DNA and assigned each person a genetic risk score. The score is based on the number of genetic variants a person carries that are known to be linked to depression risk. People with the lowest genetic risk scores were 25 percent less likely to develop depression than those with the highest scores, a much smaller effect than lifestyle factors.
Among people with high, medium and low genetic risk for depression, the research team further found that a healthy lifestyle can reduce the risk of depression. This study highlights the importance of a healthy lifestyle in preventing depression, regardless of a person's genetic risk.
Professor Barbara Sahakian, from the Department of Psychiatry at the University of Cambridge, said: "While our DNA (i.e. our genetic makeup) can increase our risk of depression, we have shown that a healthy lifestyle may be even more important. Some of these lifestyle factors are within our control to a certain extent, so finding ways to improve them - for example, making sure we get a good night's sleep and go out to see friends - could make a real difference to people's lives."
Understand the basic mechanics
To understand why a healthy lifestyle may reduce the risk of depression, the team looked at a number of other factors.
First, they examined MRI brain scans from nearly 33,000 participants and found that larger size in some areas of the brain - with more neurons and connections - was associated with a healthier lifestyle. These areas include the globus pallidus, thalamus, amygdala, and hippocampus.
Next, the team looked for markers in the blood that indicated problems with the immune system or metabolism (how we process food and produce energy). Among the markers found to be related to lifestyle are C-reactive protein, a molecule produced by the body in response to stress, and triglycerides, one of the main forms of fat used by the body to store energy.
These links are supported by some previous research. For example, stress in life can affect our ability to regulate blood sugar, which can lead to decreased immune function and accelerate age-related damage to cells and molecules in the body. A lack of physical activity and sleep impairs the body's ability to cope with stress. Studies have found that loneliness and lack of social support increase the risk of infection and increase markers of immune deficiency.
The team found that pathways from lifestyle to immune and metabolic function were most important. In other words, a poor lifestyle affects our immune system and metabolism, which in turn increases our risk of depression.
Dr Christelle Langley, from the Department of Psychiatry at the University of Cambridge, said: "We're used to thinking that a healthy lifestyle is important for our physical health, but it's just as important for our mental health. Not only is it good for our brain health and cognitive abilities, it also indirectly promotes a healthier immune system and better metabolism."
Professor Feng Jianfeng from Fudan University and the University of Warwick added: "We know that depression can start as early as adolescence or young adulthood, so educating young people about the importance of a healthy lifestyle and its impact on mental health should start in school."