Women’s Health Initiative:   A study designed by the National Institutes of Health and its National Heart, Lung and Blood Institute to determine the effects of synthetic hormone therapy on heart disease, osteoporosis, breast and colorectal cancer in post-menopausal women, 50 to 79 years of age.  Published in 2002, that study has been criticized for its flawed design: 

• Women with menopausal symptoms, such as hot flashes or night sweats, were excluded from the study.  Those are the women who may have benefitted most from hormone replacement.
• All of the study participants were post-menopausal with an average age of 64.  That means that those women, on average, had more than 10 years without sex hormones in which to develop diseases that hormone replacement may have prevented.
• The women were not prescreened for heart disease.  It is reasonable to conclude that some of the women began the study with pre-exisiting heart disease. 
• The study used synthetic hormones, which are chemically different than natural bioidentical hormones.  Synthetic hormones react and are metabolized differently in the body.  Oral synthetic hormones (Premarin or Prempro) are pro-inflammatory and can act as toxins in the body.
• The hormone doses used were nearly twice what are currently recommended.

Reanalysis of the study results were:

• Heart Disease:  Although initially reported as an increase in cardiovascular events, subsequent review of the data has shown no significant effect, either positive or negative, in the entire study population of women using oral synthetic hormones, Premarin or Prempro.  There was neither a protective effect on cardiovascular prevention nor an adverse effect on cardiovascular outcomes.  In the observational arm of the study, which included younger women within 5 years of menopause with typical menopausal symptoms, there was a statistically significant cardiovascular protective effect due to hormone therapy.
• Breast Cancer:  Taking into account all the other conventional risk factors for breast cancer, there was no statistically significant increase in breast cancer risk due to synthetic estrogen hormone therapy up to 5.6 years.  There was a slight increase in risk with the addition of synthetic progestins.  The French E3N study (2007) suggested that natural bioidentical progesterone therapy does not have an increased breast cancer risk
• Osteoporosis:  This was the first study to demonstrate a statistically significant increase in mineral bone density and a decrease in osteoporotic fracture rate with hormone replacement.
• Colon Cancer:  A reduction in colon cancer incidence was also noted in the hormone treated women.
• Total Mortality:  Women under age 60 and/or less than 10 years since the onset of menopause had a 30% reduction in total mortality due to hormone therapy.