Vitamin D—how much is best? How much is toxic?

·      Vitamin D is crucial for many non-skeletal functions including immune system regulation.

·      Numerous factors can interfere with vitamin D effectiveness, and there is significant individual variation in response to vitamin D.

·      Some individuals require very high doses for therapeutic effectiveness.

·      PTH (parathyroid hormone) levels in response to supplementation are a gauge of VDR (vitamin D receptor) response.

·      Toxicity is extremely rare; professionally managed, even ultra-high therapeutic doses have been given without toxicity.