Testosterone therapy (TRT) could lower the risk of heart attack, stroke, and all-cause mortality in patients with already-low testosterone levels, according to results from a 15-year-long VA study involving 83,000 male veterans.

The study used the largest cohort of patients and the longest follow-up for testosterone therapy to date. Results were published in the European Heart Journal.

Dr. Rajat Barua, a cardiologist and a major author of the paper, explained the significance of the findings: “It is the first study to demonstrate that significant benefit is observed only if the dose is adequate to normalize the total testosterone levels.”

“In this study of men, without previous history [heart attack] or stroke, with low testosterone levels, normalization of testosterone levels using TRT is associated with lower mortality, fewer [heart attacks], and strokes,” she said.

Researchers analyzed records of 83,010 vets, all with lowered testosterone levels. The men were divided into three groups; two of the groups received TRT, and the other group remained untreated. The groups receiving TRT with split into two treatment goals; treatment of the first group focused on restoring testosterone to normal levels, where the second group’s treatment merely focused on increasing levels (though not necessarily up to to normal levels). About four to six years after receiving TRT, researchers did a follow-up survey.

Surprisingly, men who were able to restore their testosterone levels to normal were shown to be 24 percent less likely to have a heart attack and 36 percent less likely to have a stroke during the 4-6 year follow-up period, in comparison to men who received no treatment. Also, during the follow-up period, men who restored testosterone to normal levels were 56 percent less likely to die than untreated men.

Researchers wrote in the study that future studies will need to clarify the effects of testosterone on the cardiovascular system.