remember the zinc bubba!
no matter how much time you spend in the sun, after cholecalciferol is synthesized in the skin, stage two is it heads to the liver for hydroxylation.
zinc is very important for liver function. i don't have the study at my fingertips but i saw one where the researchers observed reversal of alcohol-induced liver damage with zinc treatment.
zinc is involved in hydroxylation in a way i have not quite nailed down yet, but i have seen what happens to D3 dose response when i'm deficient and replete in zinc.
"Zinc is a good Lewis acid, making it a useful catalytic agent in hydroxylation and other enzymatic reactions..."
http://books.nap.edu/openbook.php?recor ... 6&page=446
"Zinc is defined as a Lewis acid, and its action as an electron acceptor contributes to its catalytic activity in many of these enzymes ... The structural role of zinc involves proteins that form domains capable of zinc coordination, which facilitates protein folding to produce biologically active molecules. The vast majority of such proteins form a 'zinc finger-like' structure ... Examples include ... specific factors such as ... vitamin D receptors."