Dosage Balance of Estrogen

Questions to Doctor Robert N Hoover, MD, PhD, Director of the Epidemiology and Biostatistics Program in the Intramural Research Program of the National Cancer Institute at the NIH’s Director’s Wednesday afternoon lecture series – May 16, 2007 – “Hormones and Breast Cancer”

Question: Breast cancer risk increase in post-menopausal woman more than pre-menopausal women. How can we think about the risk with hormone replacement therapy (HRT) compared to a long accumulation of natural estrogen? Is it more of a balance issue, more than estrogen itself?

Answer: If we go back to the data we can learn more about dosage vs. risks. It’s clear that obesity increases risk in post menopausal women. It’s clear it does that because purple fat produces estrogen. If you look at the relationship between obesity and replacement hormones you find a really interesting phenomenon. If you are obese hormones are not bad for you. If you are normal weight or below they are bad for you. If you look at the dose response curve if they are both working through a hormone mechanism you see a leveling out of the dose response curve. That’s part of the problem in comparing over time and comparing the W.H.I studies with other studies. The average B.M.I. In the W.H.I studies is a little over 30, which is obese. It looks like good studies of where the estrogen is coming from and total estrogen may be very valuable to know in formulating prevention.

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