Another difference between the two studies is the kind of hormone used. WHI used equine estrogen, which comes from horses, and the Danish study used 17-beta estradiol, which comes from humans. Women who had hysterectomies took additional differing hormones.
Schierbeck said because the hormones themselves are different, the dosages cannot be compared.
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 KEEPS trial findings 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.
Ouyang, the 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.