Greetings, and thanks for all the work you do.
I have a question regarding dosage and it's relationship to blood plasma levels of progesterone.
On your website I found the following:
"The typical 20-40mg/day that is recommended does not raise levels to that found in the luteal phase. One study found that using 40mg/day...
"...only low plasma progesterone levels were found (median 2.5 nmol/l)"
The ranges for the luteal phase are 15.9 - 63.6 nmol/L (5 to 20 ng/ml). Men secrete <3.18 nmol/L (<1 ng/ml). For more information see Hormone Testing."
However, I've come across some interesting research on the Virginia Hopkins site that states that blood serum levels are the wrong tests to use, with reference to scientific research that shows that they don't accurately show absorption of progesterone. That the progesterone is absorbed into the red blood cells rather than in the watery serum. And that saliva tests are a much more accurate test to use.
"Direct Comparison of Plasma and Saliva Levels After Topical Progesterone Application Dollbaum CM, Duwe GF. Absorption of progesterone after topical application: plasma and saliva levels. Presented at the 7th Annual Meeting of the American Menopause Society, 1997.
The last reference is particularly revealing. Creams with varying concentrations of progesterone were applied to menopausal women after which both plasma and saliva levels were measure. The results are illustrated below.
When only 0.34 mg of progesterone was applied topically, the plasma level rose 39 percent, whereas saliva level rose 5-fold. This indicates that only a small portion of the added progesterone entered the plasma, whereas the saliva clearly showed a hefty increase of bioavailable progesterone. When an 88-fold larger dose was applied topically, the plasma level rose only 3.6-fold while the simultaneous saliva level rose 57-fold. This indicates that only the saliva reflected the great increase in absorbed bioavailable progesterone. The progesterone found in the saliva obviously was blood-borne, but it should be clear that the portion of the blood carrying the progesterone was not the plasma (serum) but, rather, was via red blood cells.
In all situations, however, it should be clear that plasma progesterone levels are not indicative of the true level of bioavailable progesterone such as is obtained from topical application. Saliva levels are far more appropriate for this purpose.
Could you comment on this? And specifically what Dr. John Lee stated, that most women should be using around 15-20mg per day (perhaps higher in the first few months to deal with side-effects of established estrogen dominance), but then reduce down to 15-20mg per day as a long-term supplement?