I've checked my 25-OHD levels before (which prompted my doctor to recommend vitamin D supplements) and 6 months after. 95% of the population need supplementati

I've checked my 25-OHD levels before (which prompted my doctor to recommend vitamin D supplements) and 6 months after. 95% of the population need supplementation with 1700 UI to reach a serum level of 75nmol/L (considered optimal) [1]. Men can metabolize 3000-5000 UI [2]. The body adapts to higher doses by stopping solar synthesis thus we can tolerate up to 10000 UI [3]. Also vitamin D is a fat soluble vitamin and a supplement isn't necessarily absorbed well. Thus 2000 UI is generally recommended for individuals that have sub-optimal levels (this was a prescription from my doctor which is fairly standard) and it isn't considered toxic if you take up to 10000 UI. [1]: https://www.ncbi.nlm.nih.gov/pubmed/17344484 https://www.ncbi.nlm.nih.gov/pubmed/17344484 [2]: https://www.ncbi.nlm.nih.gov/pubmed/12499343 https://www.ncbi.nlm.nih.gov/pubmed/12499343 [3]: https://www.ncbi.nlm.nih.gov/pubmed/10232622 https://www.ncbi.nlm.nih.gov/pubmed/10232622