Being physically active lowers the risk of depression by 16 percent, according to a University of College London study.

The researchers said that people, who were physically active at least three times a week, reported fewer depressive symptoms. And those with more symptoms were less active, particularly at younger ages.

The finding suggests that depressive symptoms could be considered a barrier to activity in young adulthood. Engaging in physical activity could significantly improve mental and physical health and reduce obesity, heart disease and diabetes risk.

"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 percent," said Dr Snehal Pinto Pereira of the UCL Institute of Child Health, lead author of the study, in a press release.

"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."

For the study, the researchers followed 11,135 people, born in 1958, up until the age of 50 and recorded their depressive symptoms and levels of physical activity in adulthood. To assess depressive symptoms and psychological distress, the participants completed questionnaires at ages 23, 33, 42, and 50.

They found that each additional activity session per week lowered depression by 6 percent. The participants who reported more depressive symptoms at age 23 were more likely to be less physically active. However, the relationship weakened as they grew older.

"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," said Professor Mark Petticrew of the London School of Hygiene & Tropical Medicine, Director of the Public Health Research Consortium.