The prostate gland depends on testosterone for growth and development. Prostate cells, both noncancer and cancer, do too. This is why prostate cancer is sometimes referred to as a hormone-dependent cancer. Higher levels of circulating testosterone lead to higher concentrations in the prostate, and this appears to increase the risk of clinically significant prostate cancer. However, higher testosterone levels are not consistently found in prostate cancer patients, so there is more to the relationship.

A possible protective role of exercise has been proposed based on its ability to lower testosterone levels and to boost the immune system. Exercise causes a temporary reduction in testosterone, so regular exercise can reduce long-term exposure to testosterone. And chronic exercise has been shown to increase the number and activity of natural killer cells, which are part of the immune system that attack cancer cells.

Based on these effects, it seems that exercise should be beneficial, but the evidence concerning the impact of exercise on prostate cancer risk is inconclusive. In a review of 17 epidemiological studies of varying quality, 9 showed a beneficial effect, 5 no effect, and the other 3 actually showed an increased risk related to exercise or physical activity. None of the studies, however, provided conclusive proof, but taken together, they seem to support a weak beneficial effect of regular exercise on prostate cancer risk.

The challenge is proving that men who exercise regularly develop less prostate cancer when all other factors are the same. This requires a prospective long-term randomized study, and this probably will never be done. The best long-term prospective studies that looked at habitual physical activity in adulthood are encouraging, however.

A study of nearly 18,000 alumni of Harvard University showed that those who maintained a high level of physical activity were about half as likely to develop prostate cancer after the age of 70 as those who were least active. Another prospective study evaluated the level of physical fitness, as well as physical activity, on the risk of prostate cancer. Higher fitness levels were associated with lower risk in men under 60, but not in older men. And men who expended more than 1,000 kcal per week in exercise had lower risk than those who did not get this much exercise. The best long-term study of men's health is the Health Professionals Follow-up Study. It began in 1986 and has followed over 47,000 men in various health occupations since then. Data was collected in the beginning, and periodically through the study, on many factors including physical activity. The only positive result through 1994 was that at least 3 hours per week of vigorous physical activity was associated with a reduced risk of metastatic prostate cancer. But no relationship was observed between physical activity and the incidence of total or advanced prostate cancer. The same study, however, found an inverse relation between physical activity and BPH, more activity meant a lower likelihood of urinary symptoms or surgery for BPH. Walking 2–3 hours per week was enough to lower the risk of BPH.

The bottom line is that questions remain about the relation between exercise and prostate cancer, but there is no question that regular exercise is good for general health. So, it is wise to get some moderate exercise on most days of the week, and you may be protecting yourself from prostate problems, too.