Quote:
Originally Posted by Azure
Every single study ever done has shown that you have to literally take 50,000IU of Vitamin D PER DAY, for several months before it becomes a problem. In other words, since Vitamin D usually comes in pills of 1000IU, that would be 50 of those pills per day. That is insane and extremely unlikely that anyone does that.
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50,000 IU is where toxicity has clearly been observed, but there's basically not much data between 10,000 IU and 50,000 IU. Dose-response relationships suggest toxic effects probably begin somewhere between 10,000 and 40,000 IU. Still a pretty high amount. IOM recommended 4000 IU as the upper limit mostly because there aren't really many studies looking at adverse effects of vitamin D, and those that exist are relatively short-term with incomplete monitoring of possible effects and not enough statistical power to detect much. IOM also didn't view the evidence as supporting any benefits from doses above 4000 IU in their 2011 evaluation.
This also only applies for adults - in infants effects have been observed as low as 1800 IU, which is why recommended doses for infants and children are lower than for adults.