Every year, millions of women worldwide enter menopause, a universal female experience. Although some women sail through the transition with few problems, three of every four experience symptoms due to the wide fluctuations of the female hormones estrogen and progesterone during this time, and one in four experiences major symptoms. The most common symptoms include bothersome hot flashes, drenching night sweats, disturbed sleep, mood swings, vaginal dryness, concerns about sexuality, and worries about memory slippage-all of which may affect a woman’s most important relationships and her ability to function effectively at home and/or at work.

Although these symptoms can be quite troubling in the short term, the good news is that most symptoms will eventually subside over time as the hormonal tempest calms and one’s body adjusts to its new steady state of lower estrogen levels.

In the meantime, however, women are faced with one of the most complex healthcare decisions that many have ever had to make: to take or not to take hormone therapy. Many women (and their doctors) feel that they are in great need of guideposts in making informed and rational choices about this treatment.

There is little debate that hormone therapy offers highly effective relief from hot flashes and some (though not all) of the other menopause symptoms mentioned-it clearly does! Where the complexity arises is with regard to hormone therapy’s safety and whether benefits will outweigh risks. Only a short time ago, hormone therapy was considered fairly safe for most women. But a seismic shift in attitudes toward hormone therapy has occurred in recent years because of apparent discrepancies among results of different types of studies. Dozens of observational studies, which examine large numbers of people over long periods of time and record their health-related characteristics and behavior in relation to their health outcomes, have suggested major health benefits of hormone therapy, including reductions in heart disease, hip fractures, and colon cancer, as well as major risks, such as breast cancer, stroke, and blood clots in the legs or lungs. More recent findings from randomized clinical trials, which use a figurative flip of the coin to assign either an active treatment or an inactive placebo to participants, have not only appeared to refute the idea that hormone therapy protects the heart but also suggest it may actually increase the risk of heart disease.

The largest of these clinical trials, which my colleagues and I carried out as part of a huge study called the Women’s Health Initiative, assigned more than 27,000 women to a five- to seven-year course of hormone therapy or placebo to determine the impact of such treatment on a myriad of health outcomes. The heart disease findings became major news and convinced many women and their healthcare providers that the potential risks of hormone therapy outweighed the potential benefits. Women began to abandon hormone therapy in droves, feeling betrayed by the earlier assurances of its benefits.

While the pendulum has swung from the view that hormone therapy is good for all women to the view that it’s harmful for all women, both positions are oversimplifications that have confused and alarmed women, not to mention their doctors.

In my opinion, the answer is much more subtle and individual. A “one-size-fits-all” approach is inappropriate, yet very few physicians can provide women with truly satisfactory answers to their questions about hormone therapy-that is, answers tailored to a patient’s particular situation and health profile. (Along with doctors, nurse practitioners and other health professionals are on the front line of giving advice and providing care to women as they navigate the menopausal transition. Although for brevity’s sake I tend to use the words doctor or physician throughout this book, in most instances what I am saying also applies to other healthcare providers.)

After initially giving up hormone therapy, many women are now finding that their untreated menopausal symptoms are eroding their quality of life. In 2004, the American College of Obstetricians and Gynecologists stated that 25 percent of U.S. women who had stopped taking hormone therapy had restarted it-a mere two years after the Women’s Health Initiative trial reported that such therapy increased the risk of cardiovascular disease. They apparently found the symptoms simply unbearable.

But how did it happen that decades of research suggested heart protection from hormone therapy only to have clinical trials, when finally undertaken, seem to show the opposite? What are the reasons for such discrepancies between earlier and later research? And why am I now saying that the new conclusion that hormone therapy is “bad” for all women is an inaccurate oversimplification?

Only in the past year have we come to a “unifying theory” that can explain the apparent discrepancies in the research and that can help women and their doctors make appropriate use of hormone therapy. I have had the privilege of being a lead investigator on two of the largest and most comprehensive research studies on the health of U.S. women undertaken to date-the Nurses’ Health Study, which has observationally followed more than 121,000 female nurses for three decades and is still going strong, and the Women’s Health Initiative, mentioned previously. My colleagues and I developed the unifying theory based on detailed analyses of data from these and other observational studies and randomized clinical trials. Some of the results have been recently published, and others will appear in the medical literature in the coming months. I have also had the opportunity to become involved with a new randomized clinical trial testing low-dose hormone therapy in recently menopausal women.  This trial,  the Kronos Early Estrogen Prevention Study (KEEPS), is assessing the effects of oral versus patch estrogen on the development of atherosclerosis as well as on quality of life and memory and thinking ability.