What I don't understand is how it's possible for 90% of people to have a vitamin D deficiency, or whatever that crazy number was. Surely by that point it's just normal?
If everyone is being told to get 10x less vitamin d than they really need, seems easy
Vit d deficiency is a known problem because of our indoor lives and sunscreen culture, so FDA requires by law supplementation of foods. Like milk. But because the RDA is wrong, these foods get supplemented with insufficient amounts.
Case in point, seasonally adjusted the typical American gets in a day average ~1800iu from the sun and ~200iu from supplemented dietary intake (2000iu total, deficient). If we were to acknowledge the RDA is wrong then milk etc could have 30x more supplementation bringing the average up and filling the gap better