Men over 50 who have higher levels of testosterone have a higher risk of prostate cancer, U.S. researchers reported on Sunday.

The findings may mean that men should be cautious about testosterone replacement therapy, being tested in older men who see a decline in general health and vigor.

A study of more than 750 men showed those with the highest levels of free testosterone in the blood were the most likely to have prostate cancer.

“Since testosterone replacement therapy increases the amount of free testosterone in the blood, older men considering or receiving testosterone replacement should be counseled as to the association until data from long-term clinical trials becomes available,” said Dr. Kellogg Parsons, a urologist at Johns Hopkins University who led the study, said in a statement.

The association between free testosterone and prostate cancer risk in older men was not affected by height, weight, percent of body fat or muscle mass, Parsons told a meeting of the American Urological Association in San Francisco.

Another Johns Hopkins team found that obese men are more likely than men with normal weight to have high levels of prostate specific antigen, or PSA, which is overproduced when the prostate becomes cancerous.

“Our results show that moderately and severely obese men were at an increased risk for high PSA levels after surgery and therefore are likely to have prostate cancer recurrence,” said Dr. Stephen Freedland, who led the study.

His team studied 1,106 patients treated at five Veteran’s Administration and military hospitals across the country.

“Our findings add to the burgeoning list of chronic and deadly diseases associated with obesity and underscore the importance of this major public health problem,” Freedland said.

Obesity is also linked with pancreatic, breast and colon cancer, as well as heart disease and diabetes.

Prostate cancer affects 221,000 American men a year and kills 29,000.