skin produces what the works with calcium for some body processes
Vitamin D comes from two sources. It is made in the skin through direct exposure to sunlight, and it comes from the diet. The body's ability to produce vitamin D from exposure to sunlight and to absorb calcium and vitamin D decreases with age. Getting enough vitamin D helps the body absorb calcium and also helps the kidneys break down and incorporate (resorb) calcium that would otherwise be excreted.