Cis4me wrote:Everything I've read suggests that the 30-minute half-life is based on the blood levels being above the kidney threshold, the point where the kidneys send the vitamin c to the urine rather than back into the blood. Once your blood levels drop below that amount, the kidneys are no longer actively excreting vitamin C and the half-life becomes considerably longer (on the order of weeks).
I have not seen any studies that prove or disprove this (I wonder why? ), but I've suspected that when under stress, the half-life is considerably shorter due to the Vitamin C being used as well as being excreted.
This idea is interesting, and it may be true, but I don't really think so. Various substances and drugs have different
pharmakinetic half-lives, even though the kidneys regulate blood levels. Certainly spillage into the urine has something to do with this, but any measurement with 200 mg or less of ascorbate would have little or nothing to do with kidney spillage. I think the work in Sherry Lewin's lab showing the half-life of vitamin C as ascorbic acid in water offers a better explanation. The vitamin breaks down to 50% of its original value after 4 hours in tape water.
Scurvy doesn't set in for 3-5 weeks or so without vitamin C intake, and the "half life" of vitamin C in tissues (already inside cells) is around 27 days. So this "half-life" in cells is different than the half life of ascorbate traveling through the blood.
Owen R. Fonorow
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