Higher levels of testosterone, the principal male sex hormone, but present in women, may put women at greater heart risk, U.S. researchers said.

The study, published in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism, found women with the highest testosterone levels -- in the top 25 percent of this study group -- were three times as likely to have coronary heart disease compared to women with lower testosterone levels.

The researchers, who measured levels of testosterone in 344 women between the ages of 65-98, also found women in the top 25 percent three times as likely to have a group of metabolic risk factors called the metabolic syndrome -- in particular they had a greater degree of insulin resistance where the body does not use insulin efficiently.

"For many years, androgens like testosterone were thought to play a significant role in men only and to be largely irrelevant in women," study researcher Dr. Anne Cappola of the University of Pennsylvania School of Medicine in Philadelphia said in a statement.

"Further studies are needed to determine if a causal relationship exists between testosterone and insulin resistance and to provide more insight into the role testosterone plays in the pathogenesis of cardiovascular disease in women."