Study finds too much can be as ineffective as too little.
You’re probably well aware of running’s and other activities’ positive effect on your mental health. That’s especially true for many people this time of year, with less daylight contributing to seasonal affective disorder. But if some exercise is good at warding off the blues, is more inherently better?
Not necessarily, according to a study published in Preventive Medicine. Researchers compared self-reported data from more than 7,600 Americans on two matters: mental health, as measured by a standardized depression score, and hours per week of physical activity. Not surprisingly, mental health was better in people who reported some physical activity than in those who said they were sedentary. Moreover, as you can see in the graph below, there were marked differences in mental health with just a little physical activity, supporting the notion that the biggest gains from exercise often come from moving from being sedentary to just slightly active.
After about two hours per week of activity, however, there wasn’t significant continued gain in mental health. And then, after about 7.5 hours of physical activity, the gains in mental health plateued, and then started to reverse. That reversal was ever so slight at first, as weekly physical activity climbed to 10 hours. But with more and more activity, the mental-health benefits of exercise declined significantly. Nearing 25 hours a week, reported mental health was no better than in barely active people. At the extreme end of the scale–a reported five hours a day of vigorous activity–mental health was as bad as in sedentary people.
Of course, people who average five hours of exercise a day might very well have mental health issues not amenable simply to a good workout. And some of the sedentary people may be so depressed that regular exercise seems impossible to them. But for most of us between the two extremes, “[t]he optimal threshold volume for mental health benefits was of 2.5 to 7.5 [hours] of weekly physical activity,” the researchers concluded.
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