Heart disease is one of the greatest killers in America, and high testosterone levels may be what puts men at risk. Those were the findings from a new study out of Harvard, and could lead to a new risk factor for heart disease in men. The results were presented at ENDO 2015, the 97th annual meeting of the Endocrine Society.

"These observations may help explain why men have a higher risk of cardiovascular disease," said the study’s lead researcher Dr. Elaine Yu, a professor at Harvard Medical School, in a press release. Yu and her team studied the testosterone levels of 400 men between the ages of 20 and 50, and compared them to their cholesterol levels in order to figure out whether testosterone had any effect on their risk of heart disease.

Each man received the drug gosereline to suppress his own testosterone and estrogen levels. Then, half of them received either a placebo or one of four doses of testosterone gel — some of which brought their testosterone levels down to what they were before puberty. The other half of the participants also received a drug called anatrozole, which blocked testosterone's conversion to estrogen, thus making their estrogen levels especially low. 

The higher a man’s testosterone level was, the lower their “good” cholesterol levels dropped. The drugs seemed to have no effect on “bad” cholesterol levels (low-density lipoprotein cholesterol). The female hormone estrogen, which is in both men and women, had no effect on the men's risk, however, it did lead to worsening insulin resistance and the accumulation of more fat in muscle.

Cardiovascular disease (CVD) is the leading cause of death for both men and women, according to the American Heart Association, however, men are at a higher risk. More than one in three men have CVD, threatening over 8.8 million lives every day in America. Now that researchers know high testosterone levels may explain the differences in risk between men and women, they have an additional risk factor to work with.