In men, testosterone is responsible for sustaining sperm production, sex drive, facial and body hair, muscle size and strength, fat distribution, red blood cell production, and bone density. Low testosterone levels can lead to a whole host of problems, including weight increase, reduced energy, loss of bone density, reduced muscle mass, increased body fat, depression and difficulty concentrating. Unfortunately, a decreasing level of testosterone is a natural part of the aging process.

There is, however, some new hope, particularly for overweight men. It comes in the form of a new study from researchers out of Tsukuba University and Ryutsu Keizai University in Japan who found that twelve weeks of aerobic exercise can significantly boost testosterone levels in overweight and obese men. The more vigorous the exercise, the more significant the testosterone gain.

The research team compared 16 normal weight men to 28 overweight to obese men, none of whom were regular exercisers. At baseline, the overweight/obese men had significantly lower total, free and bio-available testosterone level than normal weight men. All of the volunteers in the study completed a 12-week aerobic exercise plan that entailed 40 to 60 minutes of walking or jogging on just one to three days per week. Testosterone levels were also recorded at the end of the study.

While their testosterone was still at lower levels than the normal weight men at baseline, overweight/obese men saw a meaningful increase in all measured testosterone levels. This effect was particularly obvious among the men who exercised vigorously. However, the exercise intervention had no significant effect on testosterone levels in the normal weight men. Not only did testosterone levels rise, but body weight also significantly decreased following the exercise intervention in the overweight/obese volunteer segment.

“I think decrease in body mass is one of the factors for increasing serum testosterone levels,” said Hiroshi Kumagai, lead researcher on the study. “However, the degree of weight loss is small, and we found that the increase in vigorous physical activity was independently associated with the increase in serum testosterone levels. So, it seems the increase in physical activity, especially vigorous physical activity, is the main factor for increasing serum testosterone levels.”