The Institute of Medicine of the National Academies has weighed in with a report today on Vitamin D. They’ve tripled the RDA for many adults to 600 IU from 200, and raised it to 800 for people over 70. They also doubled the upper safe boundary to 4,000 IU from 2,000.
(.pdf of the conclusions of the report HERE).
NB: they note that the chances of harm rise if you take more than 4,000 IU/day, and particularly 10,000 and over.
There is a deeply misleading, indeed borderline irresponsible, article on this in the NYTimes today by Gina Kolata, HERE. Kolata swallows the ledes, which are the huge increases in RDA and safe upper bound. Indeed, the article doesn’t even mention them!
Kolata makes all her hay from the report’s claim that most Americans don’t need to take supplements, and that some people are dosing at levels that may be dangerous. (The important area is in blood levels of Vitamin D, which the report says should be above 20 ng/ml. If indeed most Americans are well above that level, then it’s true that there isn’t much concern).
However it’s far from clear how someone who works inside during daylight hours, doesn’t drink more than a cup of milk a day (and probably significantly less) and doesn’t eat salmon or mackerel regularly is going to get anywhere near 600-800 IU/day of Vitamin D without supplementation. FYI: fortified milk has 400 IU/quart or 100 IU/cup. That’s only somewhere between 12-17% of your RDA of Vitamin D (one sixth to one eighth of what you require to remain healthy). Since Vitamin D is available in virtually no other food sources, where are we supposed to be getting it?
The lack will be particularly acute for those with dark skin or those who live at northern latitudes, and particularly during winter months when the sun is low in the sky. ... and again, for those who don’t get sun exposure at all because they work indoors during daylight hours.
While Kolata (and to some extent the authors of the study) are right to point out the dangers of overdosage, certainly for many if not most Americans the numbers simply don’t add up unless one takes a small supplement. And since there isn’t any recognized danger under 4,000 IU/day, I continue being happy taking my 1,000-2,000 IU/day supplements.