Study raises questions about HRT in diabetic women

December 02, 2002

DALLAS, Dec. 3 - In a large observational study of hormone replacement therapy (HRT) in women with diabetes, researchers have found that the effects of HRT may depend on whether a woman has had a prior heart attack, according to a report in today's rapid access Circulation: Journal of the American Heart Association.

In diabetic women who hadn't experienced a recent heart attack, HRT was associated with a 16 percent lower risk of heart attack.

"Our results are inconsistent with the results from the Women's Health Initiative (WHI), a randomized trial in women without heart disease, which reported a 30 percent increased risk of heart disease in women taking HRT compared with women on placebo," says lead author Assiamira Ferrara, M.D., Ph.D., in the division of research at the Kaiser Foundation Research Institute in Oakland, Calif.

"Dr. Ferrara's research adds to the pool of literature regarding the cardiovascular effects of HRT in postmenopausal women, but observational studies such as this, as opposed to prospective clinical trials like WHI, are not definitive and often raise more questions than they answer," says American Heart Association President Robert Bonow, M.D. "And this study does raise an important question about HRT in diabetic women - a question that can only be answered by a randomized clinical trial."

In July 2002, the Women's Health Initiative trial was stopped when the study demonstrated no benefit, and possibly an increased risk of heart attacks and strokes in women taking combined HRT (estrogen plus progestin).

"WHI is an important study that demonstrates the value of large, randomized trials to guide clinical decisions and to advise the public," said Bonow in a statement responding to the findings from WHI.

Ferrara and colleagues followed 24,420 women (average age 65) with no history of recent heart attack (within the past year), and 580 women (average age 69) with a recent heart attack.

Among women without a recent heart attack, 2,526 were using estrogen alone and 2,088 were using estrogen plus progestin. After an average of three years of follow-up, there were 256 fatal heart attacks and 854 nonfatal attacks. Current use of estrogen plus progestin was associated with a 22 percent lower rate of heart attack compared with women not taking HRT. The heart attack rate among women on estrogen alone was 11 percent lower but was not statistically significant. Risk estimates did not change significantly after researchers adjusted for heart disease risk factors, ethnicity, education and body mass index.

"Another key finding was that women taking low or medium doses of estrogen had a lower risk of heart attack, but women taking high doses did not," Ferrara says.

Women on low doses had a 51 percent lower risk and those taking medium doses had a 19 percent lower risk of heart attack than women not taking estrogen. High dose estrogen was associated with a 7 percent increased risk of heart attack.

In addition, among women without previous heart attack, the researchers found that the duration of HRT therapy also made a difference. Risk of heart attack for women using HRT for less than one year was about the same as the risk for women not taking HRT. For women on HRT longer than one year, risk of heart attack was 19 percent lower than among women not taking it.

Among the 580 women with a recent heart attack, 15 percent were using HRT at baseline. After an average follow-up of 2.5 years, women on HRT had a 78 percent higher risk of recurrent heart attack than women not taking hormones. Also among this group of women, those taking HRT for less than one year had nearly a four-fold increased risk for recurrent heart attack than women not taking HRT. There was no association between HRT and risk of recurrent heart attack in women who took hormones for one year or longer.

In an editorial that will accompany this study in the printed issue of Circulation, David M. Herrington, M.D., of Wake Forest University School of Medicine in North Carolina, notes that this study illustrates yet another "awkward reality" of clinical research on HRT.

"Observational studies like this one are likely to provide an overly optimistic view of the effect of HRT because they are not well suited to detect early adverse effects," he writes. "That is a likely explanation for the difference between the Ferrara study and WHI results." "Results from this observational study do not prove causality," says Ferrara. "More data from clinical trials in diabetic women are needed."

In the absence of such randomized clinical trials, the American Heart Association currently advises that women should not start or continue combined HRT to prevent coronary heart disease.
Co-authors are Charles P. Quesenberry, Ph.D.; Andrew J. Karter, Ph.D.; Catherine W. Njoroge; Alice S. Jacobson; and Joseph V. Selby, M.D., MPH.

American Heart Association

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