Um, yes I’ve heard of estriol. It’s made out of estrone (either directly, or via estradiol), and is naturally made by those precursors travelling through the liver, where the necessary enzymes for the conversion are found. The question is, why would anyone need to take estriol directly unless, she had a defect or deficiency in the enzymes that convert estrone and estradiol to estriol? In the absence of clear evidence that the body is unable to produce the proper balance on its own, even when an ample supply of precursors are provided, I think it makes a lot more sense to just take the precursors.
There *are* various conditions in which the body is unable to convert precursors into the needed array of hormones. Some are genetic defects in enzymes and others involve damage to key organs that produce certain of these enzymes. For example, people with kidney failure often lose the ability to convert vitamin D from dietary and/or sunlight sources into its active form (calcitriol) because the kidney is no longer able to produce a key enzyme needed for that conversion process. For those people, direct supplementation of calcitriol is needed. But it would make no sense at all (and potentially be very dangerous) to take calcitriol to correct a calcitriol deficiency, when your body is perfectly capable of converting dietary vitamin D to calcitriol, and just needs to be provided with adequate amounts of dietary vitamin D.
I take the precursors.....and a little of the estriol....and my tests reflect that....without that....well...who knows. I probably have a genetic issue somewhere since at menopause my body fell apart....almost literally. And, I do not think I am alone....also, estriol is now being seen as an issue for MS patients from what I read....so, I imagine there are quite a number of people who have conversion deficiencies. Thanks for your info.