Scientists have calculated the minimum amount of physical exercise to fight depression

Physical activity lowers their risk of developing depression. This is a consensus from countless studies. Recently, a team of scientists set out to determine how much of a difference little exercise makes.

Summarizing the results of 15 studies, a group from the University of Cambridge found that a difference begins to be felt at around half of the World Health Organization’s recommended minimum for weekly physical activity and that the benefits don’t increase much once you reach the full amount (creating yet another reason to never join CrossFit if you don’t want to).

Science in action — The researchers, who publish their findings this month in JAMA Psychiatry, compiled 15 pre-existing studies in which participants’ activities and health outcomes were measured over a median of 8.5 years. In total, the meta-analysis included data from 191,130 people.

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Incidents of depression were measured by diagnosis or symptoms of depression, as recorded by the researchers who completed the original study.

The researchers measured exercise using a unit called marginal metabolic equivalent hours of work. A metabolic equivalent minute (MET) is the energy expended during activity for one minute, expressed as a ratio of the energy expended at total rest – literally doing nothing – for one minute .

“A volume of activity equivalent to 2.5 hours of brisk walking per week was associated with a 25% lower risk of depression”

Kinesiologists have MET scores for a variety of activities, some of which are stored in this handy MET calculator. For a 160 pound person, one minute of:

  • The bike is 7.5 minutes MET
  • The salsa dance is 4.5 minutes MET
  • Window cleaning takes 3.2 MET minutes
  • Playing guitar (while standing) lasts 3 minutes MET
  • Walking at a moderate pace of about three miles per hour is 3.5 minutes MET
  • Running at eight miles per hour equals 11.8 MET minutes
  • Coal mining is 5.5 minutes MET

The authors of the new report encountered a problem when translating weekly exercise records into MET times: MET minutes and MET hours are times during which a person actually does the activity. The studies they used relied on self-reports, which obviously included pauses and interruptions. If you played basketball (6.5 minutes MET) for an hour, you probably didn’t subtract the time in which, for example, you stopped to snuggle or broke for a Gatorade or waited for your buddy picks up the ball he threw into a neighbor’s yard.

So the researchers introduced a new concept: they removed about 12% of MET hours from each activity to account for this, creating marginal metabolic equivalent task hours.

For healthy adults under age 65, the World Health Organization recommends 600 MET minutes — or 10 MET hours — per week.

The researchers found that a reduced risk of depression started for people who suffered from it half as much. Compared to adults reporting no activity, people who accumulated a marginal 4.4 hours of MET per week had an 18% reduced risk of developing depression, according to the accumulation of all these studies.

People who accumulated the marginal 8.8 hours of MET (approximately the WHO recommendation) per week had a 25% lower risk and there was no definite or noticeable benefit beyond this level of activity .

Put simply, the researchers wrote:

Accumulating a volume of activity equivalent to 2.5 hours of brisk walking per week was associated with a 25% lower risk of depression, and at half this dose the risk was 18% lower than in the absence of activity. Only minor additional benefits were seen at higher activity levels.

Why it’s a hack — The researchers looked at a few reasons why exercising at such a low frequency or intensity had a benefit.

  • Exercise releases endorphins and other good brain chemicals. Some previous research has shown that less than 60 minutes of moderate exercise triggers neuroendocrine and inflammatory responses, with no more responses from these systems with more exercise.
  • Perhaps part of the exercise-correlated reduction in depression was related to subjective measures, such as self-image and socialization.
  • People often exercise in green spaces, another depression fighter, and of course more MET minutes doesn’t directly mean more time in nature.
  • Conversely, exercise keeps people away from noise pollution and insulates indoor environments.

How it affects longevity — As the study notes, depression is the leading cause of mental health-related disease burden worldwide, affecting an estimated 280 million people. It is associated with increased mortality rates due to various conditions.

Exercise of any duration or intensity can mean exposure to green spaces, perhaps a way to combat depression.AscentXmedia/E+/Getty Images

People with regular exercise routines are less likely to suffer from depression. Some of this could be attributed to reverse causation; people who don’t have depression are more likely to have the drive to work out. But scientists believe that exercise has a protective effect on the brain.

More than a third of Americans said they never exercise in a 2021 survey. If they want to put on running shoes or hit the weight machines for better mental health, it might be good to know a minimum scientifically informed to obtain results.

Hack Score — Three out of ten walks halfway the block 👟👟👟

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