Many people live by the adage “If a little is good, a lot is better.” In some areas of life, that may well be true. But, when it comes to exercise, too much is not always healthy. A new study quantified the amount of weekly exercise that promotes mental health and found that, while too little isn’t healthy, neither is too much.

Many studies have shown a subjective association between physical activity and mental health or overall well-being, but quantifying the effects of physical activity is difficult. The new study, published in Preventive Medicine, aimed to do just that and reported that the optimal amount of exercise for improved mental health is between 2.5 and 7.5 hours each week.

The authors used data collected from the 2007 US Health Information National Trends Survey. They analyzed the self-reported physical activity data and mental health symptoms of nearly 8,000 adults. In addition to symptoms of psychological distress, depression, and anxiety and frequency and duration of physical activity that led to increased breathing, the authors considered variables such as age, employment, marital status, educational attainment, income, physical health, race, and ethnicity.

Individuals who exercised between 2.5 and 7.5 hours each week were 1.39 times more likely to have better mental health than those who exercised less or more than that. Older age, college education, higher income, and good physical health were also positively associated with mental health.

The authors report that exercising too much may lead to poor mental health, because the exercise likely occurs at the expense of other activities that are important for mental health, including family activities, social interactions, and leisure time. Or, frequent exercise may be part of a compulsion that is a symptom of poor mental health, such as anorexia nervosa or obsessive compulsive disorder, so it may not be the exercise itself that leads to poor mental health.

On the other end of the activity spectrum, sedentary behavior is also associated with poor mental health. In a 2010 study of screen-based activities among adults, sedentary behavior was independently associated with poor mental health.

The current study is limited by recall bias, but the results still support a relationship between physical activity and mental health. Many studies have attempted to quantify the amount of exercise that leads to improved physical health, and at least 30 minutes of exercise most days of the week has become synonymous with a healthy lifestyle and prevention of diseases such as diabetes, obesity, and cardiovascular disease. But, mental health is more difficult to define and diagnose, which makes its prevention harder to measure. Still, moderation seems to be the key when it comes to mental health. A balance of factors that influence mental health, including physical health, social support, and relaxation time, is likely necessary to maintain an overall sense of well-being and life satisfaction. Sometimes, only a little is good, and a lot isn’t necessarily better.

References

Hamer M, Stamatakis E, & Mishra GD (2010). Television- and screen-based activity and mental well-being in adults. American journal of preventive medicine, 38 (4), 375-80 PMID: 20307805

Kim YS, Park YS, Allegrante JP, Marks R, Ok H, Ok Cho K, & Garber CE (2012). Relationship between physical activity and general mental health. Preventive medicine, 55 (5), 458-63 PMID: 22981733

Maher JP, Doerksen SE, Elavsky S, Hyde AL, Pincus AL, Ram N, & Conroy DE (2012). A Daily Analysis of Physical Activity and Satisfaction With Life in Emerging Adults. Health psychology : official journal of the Division of Health Psychology, American Psychological Association PMID: 23088171

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