29-04-2016, 05:48
lotus: citations, gladly 
what I wrote I pulled mainly from memory but I'll pull all the citations I find and I'll try to explain the reasoning behind the 14 hour half life too.
The short half-life you mention seems to be based 1) on oral and injected progesterone, which can be short lived thanks to the liver, or first pass metabolism, as well as 2) the way hormones are bound to be transported in the blood if I'm not wrong, indicated by serum testing. all of this reasoning is not mine, but courtesy ProgesteroneTherapy.com which tends to cite good primary sources.
Transdermal progesterone, or progesterone from cream is different since it bypasses first pass to be absorbed directly into the body.
The second study you cite, first one is behind a paywall for me, actually states that transdermal is not ideal compared to oral because it results in low serum progesterone. however there is more than one way to measure, and serum hormone measurements really only read free hormone levels at the time of testing, not the other 90% or so that are bound to SHBG, etc.. this may explain why earlier research based on the assumptions of serum progesterone should be looked at differently, at least with this in mind of serum compared to salivary versus real effective levels of hormone.
There are advantages and disadvantages with either method, but supposedly salivary shows you your effective hormones floating around in blood more accurately, and this can be pinpointed to the time of the salivary sampling.
This page explains why serum progesterone, or most hormones really, don't paint a complete picture without salivary. most studies, if not all, have relied on serum rather than salivary. It's a republished letter by a Dr. David Zava http://www.progesteronetherapy.com/progesterone-test.html
So as for half life of progesterone - Transdermal progesterone from wikipedia on progesterone under "other routes"
sources they cite:
[1] https://books.google.com/books?id=AS3UBAAAQBAJ&pg=PA370 (mentions effectiveness of transdermal over oral)
[105] https://books.google.com/books?id=0IAJBgAAQBAJ&pg=PA51 (mentions time to reach peak levels of progesterone after intramuscular injection)
14 hour half life. I seem to remember the 14 hours from Progesterone Therapy under their facts and history of progesterone. so forgive me if it seems like I pulled it from thin air since I didn't cite it to begin with.
http://www.progesteronetherapy.com/history-of-progesterone.html
But I guess it might be a little longer! Wikipedia's says 16-18 hours for oral progesterone and here is what they cite for that https://books.google.com/books?id=IBxBbaDjXw0C&pg=PA74
that study also goes on to say there is no significant accumulation of progesterone or alteration of progesterone metabolism with multiple dosing over 5 days.
I would have copy pasted quotes from the google books but it won't let me select text for some reason. I also try not to see Progesterone Therapy as a primary source or final authority on the subject but I just really like all the information that the author put together there.
and for the record, I know all of this is about progesterone cream but there are other ways to raise progesterone
I just think it's a very important and misunderstood hormone, and we're still learning more about what it does for us.
what I wrote I pulled mainly from memory but I'll pull all the citations I find and I'll try to explain the reasoning behind the 14 hour half life too.
The short half-life you mention seems to be based 1) on oral and injected progesterone, which can be short lived thanks to the liver, or first pass metabolism, as well as 2) the way hormones are bound to be transported in the blood if I'm not wrong, indicated by serum testing. all of this reasoning is not mine, but courtesy ProgesteroneTherapy.com which tends to cite good primary sources.
Transdermal progesterone, or progesterone from cream is different since it bypasses first pass to be absorbed directly into the body.
The second study you cite, first one is behind a paywall for me, actually states that transdermal is not ideal compared to oral because it results in low serum progesterone. however there is more than one way to measure, and serum hormone measurements really only read free hormone levels at the time of testing, not the other 90% or so that are bound to SHBG, etc.. this may explain why earlier research based on the assumptions of serum progesterone should be looked at differently, at least with this in mind of serum compared to salivary versus real effective levels of hormone.
There are advantages and disadvantages with either method, but supposedly salivary shows you your effective hormones floating around in blood more accurately, and this can be pinpointed to the time of the salivary sampling.
This page explains why serum progesterone, or most hormones really, don't paint a complete picture without salivary. most studies, if not all, have relied on serum rather than salivary. It's a republished letter by a Dr. David Zava http://www.progesteronetherapy.com/progesterone-test.html
So as for half life of progesterone - Transdermal progesterone from wikipedia on progesterone under "other routes"
Quote:Transdermal progesterone is about 5–7 times stronger than oral progesterone.[1] This is due to the fact transdermal administration bypasses first-pass metabolism.[1] As such, 20–30 mg/day transdermal progesterone is equivalent to about 100–200 mg/day oral progesterone.[1]
With vaginal and rectal administration, a 100 mg dose of progesterone results in peak levels at 4 hours and 8 hours after dosing, respectively, with the levels achieved being in the serum luteal phase range.[105] Following peak serum concentrations, there is a gradual decline in plasma levels, and after 24 hours, serum levels typical of the follicular phase are reached.[105]
sources they cite:
[1] https://books.google.com/books?id=AS3UBAAAQBAJ&pg=PA370 (mentions effectiveness of transdermal over oral)
[105] https://books.google.com/books?id=0IAJBgAAQBAJ&pg=PA51 (mentions time to reach peak levels of progesterone after intramuscular injection)
14 hour half life. I seem to remember the 14 hours from Progesterone Therapy under their facts and history of progesterone. so forgive me if it seems like I pulled it from thin air since I didn't cite it to begin with.
http://www.progesteronetherapy.com/history-of-progesterone.html
Quote:Facts about progesterone
Molecular Formula C21H30O2 (Carbon 21, Hydrogen 30, Oxygen 2)
Molecular weight 314.46
Synonym 4-pregnene-3,20-dione
Melting point 126 C (259 F)
Bioavailability prolonged absorption
Protein binding 96%-99%
Metabolism hepatic to pregnanediols and pregnanolones
Terminal half-life 13.18 1.3
Excretion renal
But I guess it might be a little longer! Wikipedia's says 16-18 hours for oral progesterone and here is what they cite for that https://books.google.com/books?id=IBxBbaDjXw0C&pg=PA74
that study also goes on to say there is no significant accumulation of progesterone or alteration of progesterone metabolism with multiple dosing over 5 days.
I would have copy pasted quotes from the google books but it won't let me select text for some reason. I also try not to see Progesterone Therapy as a primary source or final authority on the subject but I just really like all the information that the author put together there.
and for the record, I know all of this is about progesterone cream but there are other ways to raise progesterone
I just think it's a very important and misunderstood hormone, and we're still learning more about what it does for us.