Vitamin D, known as the sunshine vitamin, exists in several forms. Of course there are the edible forms, but there is also a form inside the fatty substances in your body. This form reacts to ultraviolet sunlight in such a way that when it is exposed to ultraviolet rays it converts into a usable substance that your body can then absorb.
Vitamin D functions to help your body use minerals from other foods to build strong teeth and bones, and helps prevent tooth decay.
Vitamin D can be obtained by spending an hour or two outside on a sunny day, or eating some liver(yuck), fish liver oils, sardines, salmon, tuna, or egg yolks. You can also obtain vitamin D from milk that has been exposed to ultraviolet rays (sunlight), since the fatty substance in your skin that is converted to vitamin D also exists in milk.
A lack of an appropriate amount of vitamin D can cause soft or poorly formed bones and teeth as well as rickets. The appropriate amount of vitamin D varies from person to person, so just do your best to eat healthy and spend time outdoors and your body will do the rest!