"Acute toxicity would be caused by doses of vitamin D probably in excess of 10,000 IU/day, which result in serum 25(OH)D concentrations >150 ng/ml (>375 nmol/l). That level is clearly more than the IOM-recommended UL of 4,000 IU/day. Potential chronic toxicity would result from administration of doses above 4,000 IU/day for extended periods, possibly for years, that cause serum 25(OH)D concentrations in the 50–150 ng/ml (125–375 nmol/l) range (15)." (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6158375/)
