The current Recommended Dietary Allowance (RDA) for vitamin D is 600 IU, which is insufficient to raise blood levels to a sufficient range for deficient individuals.

“you know, the RDA right now for vitamin D is 600 IUs, of international units of vitamin D. That's what people are required to take, you know, orally as a supplement. But the question is, if you're very deficient, so deficiency is defined as 25-hydroxy vitamin D levels precursor to the hormone, less than 20 nanograms per mil. And it takes 1000 IUs a day to raise blood levels by 5 points, right? 5 nanograms per milliliter. So if you're very deficient, you're still not gonna raise yourself up to a sufficient level, which is considered 30 nanograms per mil or above.”