Vitamin D

Vitamin D is a fat soluble vitamin that is
naturally present in very few foods.  Vitamin
D promotes Calcium absorption in the gut and
maintains adequate serum calcium and phosphate
concentrations to enable normal mineralization
of bone.
Vitamin D has other roles in the body, including
modulation of cell growth, neuromuscular and
immune function, and reduction of inflammation.

Food sources include fatty fish, like tuna, mackerel,
and salmon. Foods that are fortified with vitamin D,
like dairy, soy milk, cereals, and orange juice.
Other food sources include liver, cheese, and egg
yolks.  Many times a supplement is required.