Sunscreens, especially those with SPF ratings greater than 8, effectively block synthesis of vitamin D in the skin. However, people that use such sunscreens regularly vitamin D deficiency can be avoided by dietary intake.
Vitamin D supplementation can have great benefits it should be done only under the supervision of a physician who can monitor laboratory tests and recommend proper dosage. Taking too much Vitamin D can have serious side effects.
Vitamin D Drug Interactions
The following medications increase the metabolism of vitamin D and may decrease serum D levels: Phenytoin (Dilantin), fosphenytoin (Cerebyx), phenobarbital (Luminal), carbamazepine (Tegretol), and rifampin (Rimactane).
The following medications should not be taken at the same time as vitamin D because they can decrease the intestinal absorption of vitamin D: Cholestyramine (Questran), colestipol (Colestid), orlistat (Xenical), mineral oil, and the fat substitute Olestra. The oral anti-fungal medication, ketoconazole, inhibits the 25(OH)D3-1-hydroxylase enzyme and has been found to reduce serum levels of 1,25(OH)D in healthy men . The induction of hypercalcemia by toxic levels of vitamin D may precipitate cardiac arrhythmia in patients on digitalis (Digoxin).
Vitamin D toxicity: Excessive exposure to sunlight does not lead to overproduction of vitamin D. Vitamin D toxicity is the result of overdosing on vitamin D supplements. Don’t do this! Ingestion of large quantities of vitamin D over periods of weeks or months can be severely toxic to humans and animals. In fact, baits laced with vitamin D are used very effectively as rodenticides.