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Progesterone
Is another piece of the
puzzle of hormone therapy. In women with a uterus, progesterone is required to oppose the stimulatory effects of estrogen on the uterus.
BHRT utilizes
isomolecular micronized progesterone.
HRT traditionally used Provera (medroxyprogesterone) in combination with
synthetic estrogens. Medroxyprogesterone was the progestin used in the WHI
trial.
The chemical structures of
Provera and progesterone are shown at right.
(figure obtained from http://www.tidesoflife.com/safealternative.htm)
It is generally accepted
that heart disease is responsible for at least three-fourths of the deaths in
postmenopausal women. There has been research that suggests estrogen
replacement reduces the cardiovascular risks associated with menopause.
Unfortunately, as first reported when one arm of the WHI study was stopped, the
progesterone replacement required to minimize the risk of endometrial cancer
seems to increase the risk of heart attack.
Those that support BHRT argue
that natural progesterone opposes the endometrial estrogen effects but does not
increase the risk of heart attack. Supporters quote research in rhesus
monkeys who were treated with estradiol plus Provera or natural progesterone9.
The monkeys were then administered a drug which causes constriction of arteries,
simulating a heart attack. It was reported that the subjects in the
natural progesterone group did not require pharmacologic resuscitation and
recovered more quickly from the simulated attack than the Provera group whom all
required resuscitation.
In addition, a British study of 16 postmenopausal women with coronary artery
disease received HRT with estrogen plus either Provera or natural progesterone.
Those who received natural progesterone were able to exercise significantly
longer on a treadmill test before developing symptoms which indicate reduced
blood flow to the heart11.
Proponents of HRT do not
argue that use of Provera can increase the risk of heart attacks. They do
however argue that there are not enough human tests or tests with enough humans
to provide sufficient evidence of the benefits of natural progesterone.
Supporters do offer an open label trial which assessed quality of life and costs
of therapy. There were no major differences between the two groups85.
9. Miyagawa K, Rösch J,
Stanczyk F, Hermsmeyer K. Medroxyprogesterone interferes with ovarian steroid
protection against coronary vasospasm. Nature Med. 1997;3:324-327.
11. De Ziegler D. Cardiovascular effects of the ovarian hormones. Arch Malad
Coeur Vais. 1996;89(suppl):9-16.
85. Boothby LA, Doering PL, Kipersztok S.
Bioidentical hormone therapy: a review. Menopause
2004;11:356–367.
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