Vitamin D excess and protection against sunlight-induced toxicity
THE CONTEXT
Excess dietary vitamin D can cause toxicity, and some infants develop hypercalcemia even at relatively low intakes.
Hypercalcemia and its consequences
•
Some infants are sensitive to vitamin D intakes as low as 50 μg/day and develop an elevated plasma calcium concentration.
•
The elevated calcium can cause blood vessel contraction, high blood pressure, and calcinosis, which means calcification of soft tissues.
•
In at least some cases, hypercalcemia at low vitamin D intakes results from genetic defects of calcidiol 24-hydroxylase, an enzyme involved in vitamin inactivation.
Why sunlight does not cause vitamin D poisoning
•
Excessive sunlight exposure does not cause vitamin D poisoning because the capacity to form the precursor, 7-dehydrocholesterol, is limited.
•
Prolonged exposure of previtamin D to sunlight produces inactive compounds.