Frank hypercalcemia is incredibly rare, as in: you will never experience it if you are not frankly poisoning yourself with vitamin D and if you're healthy to begin with. Most definitely not with 2,000 IU. The real danger stems from possible chronic side-effects of 25(OH)D levels >50ng/ml (acute toxicity featuring the prominent disturbance of calcium metabolism is normally seen at levels >150ng/ml). Any toxic effects are most probably mediated via the vitamin D receptor and not blood calcium, so there's no warning that you could be chronically damaging your health. There are no known benefits of levels >50ng/ml so we could play it safe for now. 5000 IU will get many of us to those levels, which is why I consider it borderline high (w/o blood testing).
hmm, andre, unfortunately there are not many meaningful markers of calcium metabolism. Ca x P, PTH, 25(OH)D and calcitriol work well for the vitamin D side of the equation and undercarboxylated osteocalcin could work as a marker of vitamin K deficiency. A million things can (and do) go wrong with calcium metabolism and we'd prefer to have it all figured out, but we haven't.
Anthony, you quoted: "The dose of vitamin D that causes significant hypercalcemia is highly variable between individuals but is rarely less than 1000 micrograms/day." That's 40'000 IU or 2-4 times the amount produced by heavy sun exposure. The risk is real, but the proposed mechanism of action (i.e. hypercalcemia) is not. Adding calcium could increase the risk further, but not vit D alone.
Edited by kismet, 03 April 2009 - 11:15 PM.