Four extra hours of weekly exercise reduce depression risk by a fifth: Study

Physical activity can significantly reduce the odds of depression, even among people who are genetically predisposed to the condition, according to a study that may lead to better clinical strategies to counter the mental disorder.

The researchers, including those from Massachusetts General Hospital in the US, said people may see a 17 percent reduction in odds of a new episode of depression for each added four-hour block of activity per week. The study, published in the journal Depression and Anxiety, analyzed the genomic and electronic health record data from nearly 8,000 participants in the Partners Healthcare Biobank -- a long-term research program designed to help scientists understand how genes and other factors affect people's health.

The researchers also followed patients who filled out a survey about their lifestyle habits such as physical activity when they enrolled in the Biobank. Over the next two years, they identified people who received diagnoses related to depression, and also calculated genetic risk scores for each participant, combining information across the entire genome into a single score that reflected on a person's inherited risk for depression.

The findings of the study revealed that people who were more physically active were less likely to develop depression, even after accounting for genetic risk. "Our findings strongly suggest that, when it comes to depression, genes are not destiny and that being physically active has the potential to neutralize the added risk of future episodes in individuals who are genetically vulnerable," said study lead author Karmel Choi from Harvard University.

The researchers said on average 35 additional minutes of physical activity each day may reduce people's risk of depression, and protect against future episodes of the illness.