By the mid-1990s, ERT had become one of the most widely prescribed medications for women in their menopausal period. Several observational studies have shown that women who were given ERT had lower risk of heart disease. However, in 2002, the results of the large Women’s Health Initiative (WHI) study have been both influential and controversial. This study involved 27,347 U.S. women ages 50-79 – 16,608 of them had a uterus and were given estrogen-plus-progestin while 10,739 had no uterus and were given estrogen alone. Unfortunately, the study concluded that ERT can increase one’s risk of developing breast cancer, heart disease, stroke, blood clots, and overall harm, which led to early stoppage of the clinical trial.  While the WHI study is considered as one of the largest clinical trials assessing the safety and efficacy of estrogen on women, several high quality studies do not agree with its results because of the following reasons:
1. The hazard ratio (HR) of the WHI study did not reach statistical significance. The authors of the WHI study reported a “significant” hazard ratio for coronary heart disease (CHD), breast cancer, blood clots, and stroke. However, other health experts who have carefully examined the WHI study suggest that the conclusions drawn were incorrect because their hazard ratio for each potential health hazard did not reach statistical significance and was based on unadjusted risk hazards. [509-510]
2. The WHI study does not even qualify as a randomized placebo-controlled study.
The reasons for this are the following: [511-515]
a. After randomization, the women were free to decide whether to continue their assigned treatment or whether to undergo diagnostic procedures.
b. Almost 50% of the women were aware of their treatment.
c. The participants received several warnings regarding increased risks of heart disease, stroke and blood clots during the study.
3. Post-hoc analyses suggest no increase in CHD in women starting estrogen treatment within 10 years of menopause. Post-hoc analyses are analyses that were not pre-planned and were conducted as additional analyses after completion of the experiment or clinical trial. Authors of the WHI study concluded that estrogen therapy had no beneficial effect on the risk of CHD and such treatment might increase CHD risk. On the contrary, post-hoc analyses found that there was no increase in CHD risk in women starting estrogen treatment within 10 years of menopause. 
4. The authors of the WHI study did not mention the other significant benefits of estrogen treatment among the participants. The authors only reported increased risk of breast cancer, heart attacks, stroke and blood clotting among women receiving estrogen therapy. They did not mention that the treatment “significantly” decreased the risk of colon cancer and hip fractures among the participants. 
5. There are some health factors that might have altered the outcome of the WHI study. The participants in the WHI study has an average BMI of 28 (overweight), one-third were hypertensive and one-half were smokers, suggesting that these factors might have significantly altered the outcome of the clinical trial. 
6. The women in the WHI study were 12-15 years past the onset of menopause. This means that the participants were without their pre-menopausal estrogen levels long enough to bring about various changes in bodily functions. For instance, when estrogen is no longer secreted at menopause, this causes a decline in bone mineral density, thereby increasing a person’s risk of fractures and osteoporosis. In addition, estrogen is crucial for maintaining normal structure and function of the blood vascular system. Once a disease has already afflicted this system, ERT will not likely reverse its negative effects.  Therefore, ERT should be used as preventive, not corrective therapy; therefore, administration of estrogen should start during the menopausal transition and not 12-15 years past the onset of menopause.
7. The WHI study actually found beneficial effects of estrogen on heart disease, breast cancer and diabetes risk as well as improvements in menopausal symptoms, joint pain and physical functioning. The authors of the WHI study found the following beneficial effects of estrogen on various health hazards: 
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