Deva Boone’s blog (an MD featured often on HN) describes a case where an extra 5000IU supplement caused neurological problems.
IIRC, there was no regard to other sources - e.g. she might have gotten 30,000 other IU per day from Milk and another amount from fish. Very unlikely - much more likely that something else made it toxic in that case.
Regardless, it is clear that the upper safe limit has significant variance and is not well characterized.
(Personally have been on 10,000IU daily for the past 7 years with no ill effects and possibly good effects, n=1 standard disclaimer)
IIRC, there was no regard to other sources - e.g. she might have gotten 30,000 other IU per day from Milk and another amount from fish. Very unlikely - much more likely that something else made it toxic in that case.
Regardless, it is clear that the upper safe limit has significant variance and is not well characterized.
(Personally have been on 10,000IU daily for the past 7 years with no ill effects and possibly good effects, n=1 standard disclaimer)