By SUSAN IPAKTCHIAN

A portion of the national Women’s Health Initiative study dealing with estrogen therapy was halted Monday by the National Institutes of Health a year before its scheduled conclusion because of concerns that the estrogen increased the risk of stroke while offering no protection against heart disease.

The stoppage affects about 11,000 postmenopausal women nationally including 230 who participated in Stanford’s portion of the trial, said Marcia Stefanick, PhD, professor (research) of medicine at the Stanford Prevention Research Center and chair of the national steering committee for the WHI study.

Local participants received letters Monday advising them to stop taking the hormone study pills and encouraging them to contact Stefanick’s office if they have questions.

Stefanick cautioned that researchers are still finalizing the data from the estrogen portion of the study, which they plan to publish in mid-April. Until then, they are informing women that the increased risk of stroke associated with the estrogen used in the study, known as conjugated equine estrogens, appears similar to what was found in a related WHI study of the combination of estrogen and progestin. In that study, there was an increase of eight strokes per year for every 10,000 women compared with those taking a placebo.

The initial data indicate that the estrogen doesn’t appear to have any effect on the risk of developing heart disease, whereas it does appear to reduce the hip fracture risk. It doesn’t appear to increase the risk of breast cancer.

“The overall picture of the benefits versus the risks of using the estrogen is reasonably well-balanced, but in the absence of any indication that it protects against heart disease the NIH felt that the increased risk of stroke among otherwise healthy women was unacceptable,” Stefanick said.

WHI was launched in 1991 to examine the most common causes of death, disability and impaired quality of life in postmenopausal women. The 15-year, multimillion-dollar effort involves more than 161,000 women nationwide.

In addition to the studies of estrogen and the estrogen-progestin combination, the study has arms examining the role of a low-fat diet in reducing breast and colon cancer; the role of calcium and vitamin D in fracture prevention; and an observational study to identify disease predictors. Those arms are continuing.

In 2002, the arm dealing with the estrogen-progestin combination was halted because of evidence that the participants experienced a greater risk of breast cancer, heart attack, stroke and blood clots.

Since then, women have received conflicting messages as to the need for hormone replacement therapy. Stefanick encouraged women to discuss their concerns with their physicians and to follow guidelines from the U.S. Food and Drug Administration.

Those guidelines say that women should consider using hormone therapy for relief of hot flashes and other symptoms related to menopause. However, women are encouraged to use the lowest hormone dose needed to achieve treatment goals and to limit the duration of the therapy.

The FDA advises against the use of hormone therapy as a method of preventing heart disease.