In one of the largest and most extensive studies of its kind, Australian researchers have found that regular exercise of any intensity can help to prevent depression, with just one hour a week enough to reap the benefits.
Led by researchers from the Black Dog Institute, the international study looked at 33,908 Norwegian adults who were taking part in the Health Study of Nord-Trøndelag County (HUNT study) -- one of the largest and most comprehensive population-based health surveys ever undertaken.
The participants were asked at the start of the research to report on how frequently they participated in exercise and at what intensity: without becoming breathless or sweating, becoming breathless and sweating, or exhausting themselves.
The participants were then followed for more than 11 years, during which time they were asked to complete a questionnaire to monitor levels of anxiety or depression.
The team also took into account factors which might affect a possible relationship between exercise and mental illness, including socio-economic and demographic factors, substance use, body mass index, physical illness and perceived social support.
The results showed that even small amounts of exercise can protect against depression, with those who reported doing no exercise at all at the start of the study showing a 44% increased chance of developing depression compared to those who were exercising one to two hours a week.
The team also found that 12 percent of cases of depression could have been prevented if participants undertook just one hour of physical activity each week, and the beneficial effect of exercise on depression was also found in both men and women and across all ages.
"We've known for some time that exercise has a role to play in treating symptoms of depression, but this is the first time we have been able to quantify the preventative potential of physical activity in terms of reducing future levels of depression," said lead author Associate Professor Samuel Harvey from Black Dog Institute and UNSW.
"With sedentary lifestyles becoming the norm worldwide, and rates of depression growing, these results are particularly pertinent as they highlight that even small lifestyle changes can reap significant mental health benefits," he concluded.
The results can be found published online in the American Journal of Psychiatry.