Editor’s Note: After the publication of Dr. David Zava’s last Health Watchers News and Views post, Hormone and Breast Cancer: the Latest Findings from the WHI, he received an attacking comment from a doctor who has been making claims for years that natural progesterone has the same effects as the synthetic progestins. Although, as an editor, I do not publish comments that attack, Dr. Zava wrote an eloquent, if technical response which adds to the dialogue about progestins, progesterone and breast cancer. We share it here for the reading pleasure of hormone biochemistry geeks everywhere!
I very much disagree with the comment that “Progestins cause more breast cancer than estrogens because they act like progesterone.” Yes, synthetic progestins increase breast cancer, but there is no evidence that progesterone does the same. Quite the contrary. Below is my argument in favor of natural progesterone as a preventive for breast cancer, with reference to the Fournier studies that address this issue.