https://vitamindforall.org/letter.html https://vitamindforall.org/letter.html is a letter that goes into why >= 4000 IU daily is recommended based on blood seru

https://vitamindforall.org/letter.html https://vitamindforall.org/letter.html is a letter that goes into why >= 4000 IU daily is recommended based on blood serum levels with more literature review.