Max "official" safe daily limit is 4000 IU currently, but the only studies I'm aware of where actual toxicity was reported started at something like 40,000 IU daily for months. Vitamin D is likely pretty safe.
No, the estimated RDA based on EPIC series of studies is 3000 IU daily and it's suspected to be on the lower side due to old people being bit overrepresented. This based on all cause mortality, various European subjects. Intake estimated by direct multiple blood levels.
Vitamin D intake vs mortality followed a very shallow U curve (almost J) and minimum was between 2000 and 4000 IU.
Vitamin D intake vs mortality followed a very shallow U curve (almost J) and minimum was between 2000 and 4000 IU.