We’ve written many times about how exercise can help reduce the risk of depression. Now scientists have finally found out just how much exercise is enough to improve your mental health.

Combining research findings from 15 studies, scientists from the University of Cambridge concluded that just half of the World Health Organization’s recommended weekly levels of physical activity is needed to reduce depression. Not only that, but they also found that the benefits are not much greater if you reach the full recommended amount.

As part of the new research, the team compiled the findings of 15 previous studies whose authors measured the activities and health outcomes of more than 191,000 participants over an average period of 8.5 years. They then measured depression using the same techniques as the original authors, including diagnoses and reports of depression symptoms.

What are METs?

For measuring physical activity, the researchers used a unit called marginal metabolic equivalent task hours. One metabolic equivalent (MET) minute is essentially the energy employed while performing any activity for one minute. MET is expressed as a ratio compared to the energy expended when fully at rest for one minute.

If you’d like to check out the MET scores of your daily activities this MET calculator can come in quite handy. But to quickly put things into perspective, one minute of cycling is 7.5 MET minutes, playing the guitar (while standing) is 3 MET minutes, running at eight miles an hour is 11.8 MET minutes, and cleaning the windows is 3.2 MET minutes.

While translating the records of weekly exercise into MET time, the scientists realized that since the previous studies relied on self-reported data the subjects probably didn’t subtract the time in which they stopped for breaks. To accommodate for this, the scientists took subtracted about 12 percent from each activity’s MET-hours, creating marginal metabolic equivalent task hours.

Half of the global recommended levels of weekly exercise

The World Health Organization’s recommended amount of weekly physical activity is 600 MET minutes or 10 MET-hours. The findings of the new study concluded that just half of that can already help reduce the risk of depression. Compared to adults who reported no physical activity at all, people who engaged in 4.4 marginal MET-hours of exercise per week had an 18 percent lower chance to suffer from depression.

Those who accumulated 8.8 marginal MET-hours weekly had a 25 percent lower risk, with no significant change in benefits when exercising more than that. As such, just 2.5 hours of brisk walking per week can help reduce your risk of depression by 25 percent. And just half of that can reduce risk by 18 percent compared to no physical activity at all.

If physical activity is generally not a priority for you, we hope these new findings will motivate you to get a little more exercise in your daily life.

Source study: JAMA Psychiatry — Association Between Physical Activity and Risk of Depression