I never thought I'd write the following sentence, but the evidence has become pretty overwhelming: Unless a woman has a history of breast cancer or has some other condition aggravated by estrogen, the benefits of postmenopausal hormone replacement therapy (HRT) far outweigh the risks.
For the past 15 years, I've been very skeptical about the safety of estrogen in both HRT (estrogen plus the hormone progestin), which women use to ease the passage into menopause, and in birth control pills (see Pilling Time). Many studies have shown that HRT increases the risk of breast cancer in postmenopausal women; others have shown no association. On balance, I felt that estrogen was a bad idea.
However, studies have also shown that estrogen helps prevent heart disease, osteoporosis (postmenopausal bone-thinning), and colon cancer, and can even reduce the risk of Alzheimer's. Women faced a stark decision: What are you more afraid of? Breast cancer? Heart disease? Osteoporosis? But the terms of the debate have changed -- and as a result, I've changed my tune.
It's been a long road for yours truly. For years, I've been astonished at the number of scientists who gamely argued that HRT poses no breast cancer risk. That seemed ridiculous. For decades, estrogen has been widely recognized as a stimulator of breast tumors in both animals and humans. It stood to reason that as growing numbers of women took estrogen, over time, we would see a steady increase in breast cancer -- and we have, at a rate of about 1 percent per year. Contrary to what some experts have claimed, the increase cannot be fully explained by earlier detection (i.e., mammography).
In addition, it has become increasingly clear that compounds which mimic estrogen -- chemicals unrelated to the hormone but that bind to cellular estrogen receptors -- have been disrupting mammalian wildlife reproduction and, quite possibly, contributing to the higher incidence of human breast cancer. (See "Breast Cancer Cover-Up," May/June 1994.)
Meanwhile, arguments in favor of estrogen to ward off heart disease and osteoporosis rubbed me the wrong way. It made no sense to throw a cancer-promoting hormone at women to prevent diseases that could be checked as effectively and more safely by quitting smoking, a low-fat diet, regular exercise, stress management, and supplemental calcium.
But now the equation has changed. Here's why: During the past few years, a scientific consensus has emerged that HRT does indeed, when used for 10 to 15 years, increase the lifetime risk of developing breast cancer (by 20 to 30 percent). Ironically, however, the latest research shows that, in addition to other health benefits, women taking HRT actually enjoy a decreased lifetime risk of breast cancer death.
Menopause marks not only the end of a woman's reproductive years, it also signals the beginning of her major-risk years for heart disease. Heart disease is by far the No. 1 killer of both older men and women, but while heart disease takes a considerable toll on men in their 40s, estrogen protects women until after menopause. Then, as their natural levels of estrogen decline, their risk of heart disease soars.
Unfortunately, few women appreciate this. Not long ago, the Gallup Organization asked women to name the leading cause of female death. Forty percent said breast cancer, while 19 percent said heart disease. In fact, 35 percent of women die from heart disease, while only 4 percent succumb to breast cancer. And among postmenopausal white women, the lifetime probability of death from heart disease is even higher -- 46 percent.
The survey respondents' mistaken assumption was to some extent understandable. Breast cancer begins claiming a significant number of lives while women are in their 40s. Heart disease doesn't surpass it until women are well into their 50s. As a result, fear of breast cancer hits hard premenopausally, and lingers long after the risk from heart disease has dwarfed it.
Recently, Dawn B. Willis, scientific program director for the American Cancer Society, provided some welcome perspective on the risks and benefits of HRT. On the risk side, a decade or so of HRT increases the risk of breast cancer by as much as 30 percent. However, HRT also significantly reduces a woman's risk of heart disease.
Some simple math shows what these figures mean: At age 50, a white woman has a 9 percent risk of developing breast cancer over the next 30 years. HRT increases that risk by approximately a third, or 3 percentage points, to about 12 percent. However, the same woman faces a 46 percent risk of developing heart disease. HRT cuts it 12 percentage points to 34 percent. Even if breast cancer and heart disease killed the same number of postmenopausal women, these numbers would argue in favor of HRT -- a 12-point reduction in heart disease risk outweighs a 3-point increase in breast cancer risk. But heart disease is much more lethal than breast cancer, which argues even more strongly in favor of HRT.
As for osteoporosis, one-quarter of white women over 45 have detectable bone-thinning, and by age 75, the figure is 90 percent. In a study of women over age 50, HRT reduced hip fracture risk from 15 to 12 percent.
As I mentioned, both heart disease and osteoporosis can be prevented without estrogen. But doing so requires lifestyle changes many American women seem unwilling to make. I'm all for encouraging a healthier lifestyle, but from a public health perspective, it's callous to insist on lifestyle transformations when HRT provides significant benefits quickly and easily without them.
What's more, two recent studies show that estrogen may help prevent Alzheimer's (which is currently destroying the minds of some 2 million American women) because it helps preserve the neurotransmitters in the brain that become impaired by the disease. Researchers from the National Institute on Aging who followed 472 postmenopausal women for 16 years found that, compared with those who had used estrogen, those who had never taken it were more than twice as likely to develop Alzheimer's. A similar study in New York showed that women taking estrogen had a 2.7 percent risk of being diagnosed with Alzheimer's; among those not taking the hormone, the risk was 8.4 percent.
In addition, HRT helps prevent colon cancer. After 50, 6 percent of white women develop colon cancer; new research shows that HRT cuts this risk to just 3 percent.
Still, breast cancer is the disease women fear most, and despite the evidence of HRT's benefits, women have rejected it in droves because of breast cancer-phobia. Fewer than 25 percent of postmenopausal women who could take HRT do so.
Which brings me to the research showing that while HRT increases risk of developing breast cancer, it also reduces risk of dying from it by a whopping 22 percent. These findings come from American Cancer Society researchers who followed 422,000 postmenopausal women for nine years. This study's enormous number of participants and its long duration give its findings considerable scientific weight.
How could a hormone that increases risk of developing breast cancer simultaneously reduce the risk of dying from it? No one knows for sure, but most studies have shown that HRT use decreases women's risk of death from breast cancer.
Don't get me wrong: I'm not urging every postmenopausal woman to take HRT. The current consensus is that those with a history of breast cancer should not take it. HRT also increases risk of gallstones, asthma, and, more rarely, blood clots in veins.
But for women who have a low risk for these conditions, and especially for those with family histories of heart disease, colon cancer, osteoporosis, or Alzheimer's, HRT is definitely something to consider.
Health columnist Michael Castleman is the author of the best-selling books Nature's Cures and The Healing Herbs (Emmaus, Penn.: Rodale Press).