The Black Dog Institute has published a study showing that regular exercise can protect against depression, even if it is just for one hour a week.
The study, which is the largest analysis of its kind, involved 33,908 healthy participants who had their exercise levels and symptoms of depression and anxiety assessed over an 11-year period.
The participants were asked to self-report how often they engaged in physical activity and at what intensity, ranging from exercise that does not cause breathlessness or sweating, exercise that does cause breathlessness and sweating and exercise that leads to exhaustion. As part of follow-up, the subjects were asked to complete a questionnaire called the Hospital Anxiety and Depression Scale, which flags up any emerging depression or anxiety symptoms.
Variables that may influence the association between mental illness and exercise were accounted for and included substance use, socio-economic and demographic factors, new-onset physical illness, perceived social support and body mass index.
As reported in the American Journal of Psychiatry, the study showed that people who do not engage in any exercise are 44% more likely to suffer from depression compared with people who exercise for one to two hours per week and that exercising for just one hour per week could have prevented 12% of depression cases. However, the study did not show that exercise had any protective effect against anxiety, with no level or intensity of exercise being associated with any reduced risk of developing the disorder.
Lead author of the study, Professor Samuel Harvey (Black Dog Institute), says that it has been known for some time that exercise plays a role in relieving symptoms of depression, but that this is the first time researchers have been able to quantify the preventative potential of physical activity in terms of reducing future levels of depression. The findings are exciting, he says, “because they show that even relatively small amounts of exercise - from one hour per week - can deliver significant protection against depression.”
Harvey and team are trying to establish exactly why exercise can have a protective effect against depression, but they suspect the benefit may be the result of the combined effects of the various physical and social benefits of engaging in physical activity.
"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," concludes Harvey.