The government is ending the last major study of estrogen, saying taking estrogen alone isn't as bad as taking it together with the hormone progestin, but it's still too risky for long-term use.
Women who took estrogen alone after menopause had a significantly increased risk of stroke, and possibly a higher risk of dementia too, the National Institutes of Health said.
Doctors long thought that using estrogen, alone or together with progestin, would keep women healthier after menopause, in such ways as reducing heart attacks and keeping the brain sharp.
Millions of women have quit using the estrogen-progestin combination since 2002, when federal scientists warned that those pills raised the risk of breast cancer, strokes and heart attacks. Scientists weren't sure whether estrogen alone was as risky.
Only women who have undergone a hysterectomy can even consider taking estrogen alone; in other women, progestin use with estrogen is crucial to protect against uterine cancer.
Now, the NIH is shutting down its study of estrogen-only use, too, telling the 11,000 women enrolled to quit their pills, essentially ending hope that estrogen alone would have some overarching usefulness that the hormone combination didn't.
The women, who were healthy 50- to 79-year-olds, took either estrogen or a dummy pill for nearly seven years. Among the findings released Tuesday:
- Estrogen alone increased the risk of a stroke as much as estrogen-progestin does. For every 10,000 women, those taking hormones suffer eight more strokes per year than nonhormone users.
- Estrogen alone had no effect, good or bad, on heart disease. In contrast, the estrogen-progestin combination increases heart attack risk by 29 percent.
- Estrogen alone didn't increase the risk of breast cancer. Again in contrast, the estrogen-progestin combination had increased that risk, by 26 percent.
Neither type of hormone therapy seems good for women's brains. Preliminary data from a related study of women 65 and older suggest those taking estrogen alone were more likely to suffer some degree of dementia than those taking a placebo, the NIH said.
Likewise, scientists announced last May that the estrogen-progestin combination doubled the risk of Alzheimer's and other forms of dementia.
Both estrogen alone and with progestin have some benefits. Both types decrease the risk of a hip fracture from bone-thinning osteoporosis, and are the more effective treatment for such symptoms of menopause as hot flashes.
But the NIH said considering the pills' other risks, only women who cannot take one of the nation's many other osteoporosis treatments should consider estrogen for that use.
The Food and Drug Administration stresses that women who use any form of estrogen to relieve menopausal symptoms should use the lowest dose for the shortest duration.
Women now taking hormone therapy, or considering it, for those two reasons must discuss their individual risk factors with their doctors, cautioned the American Society for Reproductive Medicine.
The NIH decided to stop the estrogen-only study last month, a year before its planned completion, saying enough data had been collected to assess overall risks and benefits.
The agency plans to report details of the data within two months, but released preliminary findings Tuesday to coincide with letters telling study participants to quit their pills.