Editor, Science of NAD
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some interesting studies. You can read more about me here. And check with your physician -- your physician can look at this research, too.
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Is NR Bioavailable?
Some oral NR gets converted to other precursors in the gut, liver, and bloodstream, but enough gets through as NR to make a difference...
It is clear that orally ingested NR gets broken down into a number of different precursors that replenish NAD through different pathways, which is a good thing. It is equally clear that some of the NR gets through to cells as NR and replenishes NAD through the Brenner pathway, which is an even better thing. Exactly how much NR gets through to which cells and how quickly is not clear, which is probably why is why the recommended dose of NR is about 15x higher than the RDA for Niacin, and why high doses of NR like 1,000 mg or more are used in most clinical research -- to make sure that enough gets through to have a measurable effect.
A number of studies have drawn strongly negative conclusions about the bioavailability of NR, asserting that it is "almost entirely" degraded and "nearly all" is converted to NAM.
But other studies are less certain, pointing out that "at least some gets through," and "a therapeutic amount apparently makes it through."