It is certainly a different mechanism. There are inactive isomers of pre-Vitamin D (tachysterol and lumisterol) that prevent over-production of Vitamin D from continued UV exposure.

I list these numbers to give a general idea of the levels of Vitamin D that people experience without oral supplementation.

My conclusion was that too many studies were being done to determine the correct or safe amount to supplement rather than testing regularly to determine a safe/optimal blood concentration.

Very excited for good prospective studies of Vitamin D.