[LocalPCGuy]

As has been commented elsewhere, everyone absorbs vitamin D differently, this really is a matter where someone should just get tested, if they (and their doctor) decide supplementation is needed, do so, test again, and adjust dosage accordingly until desired levels are attained.

Not medical advice here, but harmful effects from vitamin D exposure/toxicity generally only happen at very high levels, or if high doses are taken over long periods of time (as excess can be stored in fatty tissue/liver). Doctors often prescribe a very high dose (like 50,000 IUs) for individuals who are very deficient (often taken once a week, not daily) for a short period before going on a more standard (400-2,000, maybe 5,000) IU dose for maintenance.