Link Between Hormones and Heart Attacks Studied

A new study at Baylor College of Medicine is investigating whether hormone replacement therapy may cause heart attack-inducing blood clots.

"Millions of women are currently taking hormone replacement therapy, and there still are good reasons to use HRT," said Paul Bray, M.D., professor of medicine at Baylor and director of Baylor’s Thombosis Center, launched in 2000. "By combining our knowledge of genetic risk factors for heart attack and stroke and how sex hormones affect the risk for blood clotting, we hope to learn whether it is the right option for every woman."

Bray’s research team is collaborating with The Methodist Hospital gynecologists Ronald Young, M.D., director of the division of gynecology at Baylor, and Lynn Hoffman, M.D., who practices at Methodist, to recruit 120 postmenopausal women into the three-month study. Blood samples of participants will be analyzed before and after women initiate HRT.

HRT combats the symptoms of menopause resulting from decreased estrogen production that occurs when most American women stop menstruating between the ages of 45 and 55. The therapy can be given as either estrogen alone or in combination with progesterone. Premarin, the brand name for estrogen, and Prempro, which contains estrogen plus progesterone, are commonly used forms of HRT.

The 1998 Heart and Estrogen/Progestin Replacement Study, also known as HERS, found that women in the first year of the study had 53 percent more heart attacks than study participants who were not taking HRT. The risk decreased once the women had made it past the first year of the study. These findings motivated Bray to find out more about the relationship between HRT and heart attacks.

"What was surprising about the HERS study was that women taking HRT were at greater risk of heart attacks, even though HRT lowered their cholesterol," Bray said. "When we learned that the women taking HRT also had an increased risk of developing blood clots in their veins, we wondered if the missing link might be thrombosis."

Like high cholesterol, thrombosis, the medical term for blood clotting, plays a central role in developing heart attacks and strokes. A heart attack occurs when a blood clot forms where cholesterol plaque breaks away from the wall of an artery in the heart. The blood clot and plaque block the artery and prevent bloodflow to the heart, which can cause death or, if the patient survives, scarring and weakening of the heart muscle.

While at Johns Hopkins University School of Medicine in Baltimore, Bray discovered the first inherited defect in blood platelets that causes thrombosis and is a risk factor for heart attacks and stroke. His group has previously shown that platelets from women are "stickier" than platelets from men, suggesting that sex hormones might play a role in those clots that cause heart attacks and strokes.

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©2006 Texas Medical Center

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