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>>While symptoms of toxicity are unlikely at daily intakes below 10,000 IU/day, the FNB pointed to emerging science from national survey data, observational studies, and clinical trials suggesting that even lower vitamin D intakes and serum 25(OH)D levels might have adverse health effects over time.<<

First, a note on measurement of vit D3 in the blood: Don’t confuse nanomoles/liter with nanograms/milliliter. In the U.S. we tend to use the latter measurement, ng/ml. To convert to nmol/L (used in Canada, Great Britain, etc.) you need to multiply by 2.5. Thus, a level of 50 ng/ml is equivalent to 125 nmol/L.

Second, in the quote taken above from the article, note the hedging by the FNB. They admit toxicity is unlikely when supplementing at 10,000 IU, but then cite non-experimental studies that “suggest” that such levels “might” have adverse health effects. The FNB was dragged kicking and screaming into DOUBLING their previous upper limits, not raising them 10% or 25%, or even 50%, but 100%! And they did this without allowing participation by the most active vitamin D researchers. The benefits of higher blood levels of vitamin D3 are becoming apparent even to them.

There’s little doubt that getting vitamin D3 from sun or from tanning is preferred due to the automatic mechanism the body has for preventing excess accumulation. But few people do so, and supplementation then remains the only option. Besides, the older one gets, the less is absorbed through the skin, in many cases.

Now, I wouldn’t take 10,000 IU unless I knew I was starting at an exceptionally low level, and I would test regularly to make sure I wasn’t getting into a level of 100 ng/ml (250 nmol/L), but 5,000 IU/day was acknowledged even by the FNB to be required to get to the 48-60 ng/ml level, the level that the active researchers consider to be close to that required to get the optimum benefits. And people weighing 200-250 pounds are likely to need even higher levels, because weight matters too.