Regular exercise can help prevent depression, and only one hour a week can help, says a landmark study published in the American Journal of Psychiatry.

The study found that even small amounts of exercise, regardless of intensity, can protect against depression. Benefits were accrued regardless of age or gender.

The analysis, which was led by Black Dog Institute, was the largest and most extensive study of its kind. It involved 33,908 Norwegian adults whose levels of exercise and symptoms of depression and anxiety were monitored over 11 years.

The researchers found that 12 percent of cases of depression could have been prevented if participants exercised only one hour each week.

"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 Samuel Harvey.

"These findings are exciting because they show that even relatively small amounts of exercise — from one hour per week — can deliver significant protection against depression.

"We are still trying to determine exactly why exercise can have this protective effect, but we believe it is from the combined impact of the various physical and social benefits of physical activity," he said.

"These results highlight the great potential to integrate exercise into individual mental health plans and broader public health campaigns," Harvey continued. "If we can find ways to increase the population's level of physical activity even by a small amount, then this is likely to bring substantial physical and mental health benefits."

Harvey's study wasn’t the first to find that exercise reduced the risk of mental disorders. Last year, researchers from the University of Manchester found that aerobic exercise eased the symptoms of the mental disorder schizophrenia.

While medication can usually treat the hallucinations and delusions caused by the disease, patients are still plagued with cognitive defects, including poor memory and concentration. Researchers analyzed data from 10 clinical trials and found that 12 weeks of aerobic exercise, including treadmills and exercise bikes, significantly improved memory and concentration.

"We are searching for new ways to treat these aspects of the illness, and now research is increasingly suggesting that physical exercise can provide a solution," said researcher Joe Firth.