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Figure  . Estrogen lowers risk of coronary heart disease in thin women

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In a large new study, American Cancer Society (ACS) researchers found that women who use estrogen replace-ment after menopause have about a 20% lower risk of death from all causes combined than those who do not. The results, published in the American Journal of Epidemiology (2001;153:145-152) showed that the reduction in death is greatest for thin women, largely due to a lower risk of coronary heart disease. Estrogen use did not raise the overall risk of dying from all cancers combined.

Carmen Rodriguez, MD, and colleagues in the ACS epidemiology and surveillance research department, examined the effect of body mass on the link between estrogen replacement therapy (ERT) and mortality among 290,827 postmenopausal women who were free of cancer and heart disease when first enrolled in the study. The median follow-up was 12 years.

Protection Against Heart Disease

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  2. Protection Against Heart Disease
  3. Estrogen Increases Risk of Random Genetic Errors

Rodriguez et al. concluded that thin women are protected from coronary heart disease by taking estrogen replacement after menopause. Women using estrogen who were not quite as thin but were still at healthy weights lowered their heart disease risk by about 25%. In contrast, obese women did not derive any heart disease protection at all from ERT. Until recently, researchers were uncertain whether a woman's weight influenced ERT-associated protection against heart disease.

“There's little question estrogen helps protect against coronary heart disease,” says Rodriguez. “But after menopause, the main source of estrogen in women's bodies is adipose tissue. In obese women, the large amount of adipose tissue produces enough estrogen so that the amount added by ERT may not offer additional protection.”

Estrogen Increases Risk of Random Genetic Errors

  1. Top of page
  2. Protection Against Heart Disease
  3. Estrogen Increases Risk of Random Genetic Errors

On the other hand, a thin woman's risk of developing breast cancer may rise with use of ERT because estrogen can increase the rate of breast cell replication, thus increasing the risk of a random genetic error that could lead to cancer, according to Rodriguez.

ERT has minimal impact on breast cancer risk among obese women because their fat cells already produce levels of estrogen high enough to stimulate breast cell replication.

In obese women, the large amount of adipose tissue produces enough estrogen so that the amount added by ERT may not offer additional protection.

No increased risk of death from breast cancer was found in either the thin or obese women on ERT in this study. “In the time period studied (1982 to 1994), ERT was usually only prescribed to women for relief of menopausal symptoms. Women using it were more likely to be under a doctor's care, and so were more likely to have early detection of any breast cancer that did develop, reducing their chances of dying from it,” Rodriguez says.

Rodriguez notes that although the questionnaire did not ask participants about progesterone use, most other studies have not found addition of progesterone to substantially reduce estrogen's cardiovascular benefits. On the other hand, there is evidence that progesterone is responsible for much of the increased breast cancer risk associated with combined hormone re-placement therapy.

The findings from this study must be confirmed, the researchers pointed out, but the apparent lack of protection against heart disease by ERT in obese women is another reason for clinicians and patients to take an individual woman's body mass index into account when deciding about estrogen replacement.