You cannot get too much vitamin D from the sun
Skin destroys the excess vitamin D it makes, so sun exposure has never caused intoxication. The blood test measures a storage form with a half-life of about two weeks.
What the study found
Sunlight cannot overdose you, and the blood test lags weeks
Skin destroys the excess vitamin D it makes, which is why sun exposure has never caused intoxication. What a blood test measures is 25-hydroxyvitamin D, the storage form, which has a half-life of about two weeks; the active hormone it becomes lasts under four hours.
The caveat · A textbook chapter, not a trial
These are standing pharmacological facts from a clinical reference chapter rather than findings from a trial. The chapter does not say how long supplementation takes to raise a level, or the dose at which toxicity begins. Nothing in it settles what level to aim for, which is a separate and open question.