(NEW YORK) -- Researchers in Denmark have become the first to offer statistical proof that hormone therapy is not only safe for menopausal women who begin it early -- it actually reduces their risk of mortality, heart attack and heart failure.
The 16-year randomized study of about a thousand women offers new proof that the "timing hypothesis," which suggests that hormone therapy protects women from heart disease if they start it soon after their last menstrual period, is correct. Researchers also saw no difference in breast cancer risk between those who were assigned the hormone therapy and those who were not.
"It really confirms the timing hypothesis and hopefully will change the way we look at hormone therapy, so it will change the quality of life for many women," said study author Dr. Louise Schierbeck, who works in the department of endocrinology at Hvidovre Hospital in Denmark.
The women took estrogen for about ten years until 2002, when another study, the Women's Health Initiative (WHI), found significant evidence that women taking progestin and estrogen were more likely to develop aggressive breast cancer. Although WHI researchers studied 160,000 women ages 50 to 79, many of whom had chronic diseases already, Danish researchers studied 1,000 women ages 45 to 58, and excluded people who previously had had cancer or other major illnesses, according to the study text, which was published in the BMJ, formerly the British Medical Journal.
Schierbeck's colleagues used Danish hospital data to figure out how many patients died or had other health problems in 2002 and six years later. Both times, they discovered that fewer hormone therapy patients died or had heart disease than the hormone-free patients.
Researchers additionally found that fewer hormone therapy patients had breast cancer or other cancers, but because the findings were not statistically significant, they can only officially conclude that there was no difference in cancer risk for the hormone therapy group and the hormone-free group, Schierbeck said.
Although the study is much smaller than WHI, doctors in the United States are calling it "important" and "encouraging" because it shows that women can relieve their menopausal symptoms, such as night sweats and hot flashes, without worrying that the long-term hormone therapy will eventually kill them.
The study will not affect current guidelines, which recommend as little hormone therapy as possible, because larger studies will be needed to affirm the findings, several doctors agreed. They were especially interested in how the study looked at women who were on hormone therapy for 10 years, which is longer than the WHI study participants were on it.
"This study is likely to lead to a resurgence of interest in studies of how hormones affect the cardiovascular system related to age and to the level of underlying pathology," said Dr. Carl Lavie, the medical director of cardiac rehabilitation and prevention at Ochsner Clinic Foundation and Hospital in New Orleans.
Still, some medical professionals were not convinced this study is a big step at all.
"This is a non-informative study with too many shortcomings to list," said Wulf Utian, the founding president and former executive director of the North American Menopause Society, or NAMS. (Preliminary findings of a different study were announced at the NAMS annual conference in Orlando last week.)
What shortcomings? The trial had an "extremely small" number of adverse health events, no placebo control and no description of the randomization method, Utian said.
Shierbeck responded to the study size criticism by saying that she reported statistically significant results.
Pamela Ouyang, a Johns Hopkins professor, said that the 1,000 women followed for almost two decades provides an enormous number of "woman-years" worth of data. Ouyang was one of the doctors who suggested that the guidelines would be rewritten because of this study.
Every doctor interviewed said that women should discuss hormone therapy with their doctors.
Copyright 2012 ABC News Radio