Vitamin D-3 (400 IU)

he most potent source of Vitamin D is the sun. Although to be more accurate, it is the action of the sun’s energy on melanin in human skin actually produces the Vitamin D. Given the easy access to sunlight, it would seem that of all vitamins, this is one that we would never need to introduce in supplement form into our diets. And yet, this is not necessarily the case.