Being physically active three times a week reduces the odds of being depressed by approximately 16%, according to new UCL research undertaken as part of the Public Health Research Consortium.

The study, published in JAMA Psychiatry, found a two-way relationship between depression and physical activity. People who increased their weekly activity reported fewer depressive symptoms but those with more depressive symptoms were less active, particularly at younger ages.

Researchers followed 11,135 people born in 1958 up until the age of 50, recording depressive symptoms and levels of physical activity at regular intervals in adulthood. They found that each additional activity session per week reduced odds of depression by 6%. In England 19% of men and 26% of women are currently classed as 'inactive', and this study suggests that activity could significantly improve their mental as well as physical health.

"Assuming the association is causal, leisure time physical activity has a protective effect against depression. If an adult between their twenties and forties who isn't physically active became active 3 times per week, they would reduce their risk of depression by approximately 16%," says Dr Snehal Pinto Pereira of the UCL Institute of Child Health, lead author of the study. "Importantly, this effect was seen across the whole population and not just in those at high risk of clinical depression. The more physically active people were, the fewer depressive symptoms they reported. Just as someone might be a little overweight but not clinically overweight or obese, many people who are not clinically depressed could still experience some depressive symptoms."

To assess depressive symptoms, the researchers looked at participants' responses to the Malaise Inventory, a questionnaire designed to assess psychological distress at ages 23, 33, 42, and 50. The participants were also asked how often they were physically active. The relationship between activity and depressive symptoms was examined over this age range.

The study showed that people who reported more depressive symptoms at age 23 tended to be less physically active, but this effect weakened as they grew older. "This finding is important for policies designed to get people more active, because it suggests that depressive symptoms could be considered a barrier to activity in young adulthood," says Dr Pinto Pereira. By contrast, increasing the frequency of activity consistently reduced depressive symptoms across the entire age range. Previous studies investigating activity as a treatment for depression have produced mixed results, but this large longitudinal study suggests that exercise has an important role to play for mental health."

"There is some evidence to suggest that activity can be used as a treatment for depression, but our study goes beyond examining the depressed group and suggests a benefit of activity to curb depressive symptoms in the general population," says senior author Chris Power, Professor of Epidemiology and Public Health at the UCL Institute of Child Health. "If everyone was physically active at least three times a week we would expect to see a drop in depression risk, not to mention the benefits for physical health, as pointed out by other research, including reduced obesity, heart disease and diabetes risk."

Professor Mark Petticrew of the London School of Hygiene & Tropical Medicine, Director of the Public Health Research Consortium, said: "Many people are already aware of the benefits of physical activity on their general health, but we are now seeing a growing body of evidence that suggests it also has a positive effect on a person's mental well-being. This latest research highlights just how important it is to ensure that people are working and living in environments that allow them to be both physically active and mentally healthy."

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