he cited this reference
Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. However, at doses above 1 g/day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine . Results from pharmacokinetic studies indicate that oral doses of 1.25 g/day ascorbic acid produce mean peak plasma vitamin C concentrations of 135 micromol/L, which are about two times higher than those produced by consuming 200–300 mg/day ascorbic acid from vitamin C-rich foods . Pharmacokinetic modeling predicts that even doses as high as 3 g ascorbic acid taken every 4 hours would produce peak plasma concentrations of only 220 micromol/L .
Question: What is "unmetabolized" ascorbic acid - and how does it reach the urine (if it doesn't enter the blood stream?)
Question: Re: "absorption falls to less than 50% " What is the definition of "asbsorbed?" Into the blood stream? From the blood into cells? To me, this implies that fully half of dosage of one gram (or 500 mg) is not absorbed into the blood stream, but I want to understand if this is what they are saying.