While you are sun tanning, your body is actually working. Our body produces this vitamin when we are exposed to sunlight – it needs ultraviolet B rays in order to produce vitamin D. However, you have to actually be outdoors since UV rays don’t go through glass windows. Another direct source of vitamin D is food. You can increase your daily dose through fatty fish, like salmon, sardines and tuna, egg yolks, mushrooms and some dairy products. The biggest role of vitamin D is that enables absorption of calcium and phosphorus to keep bones strong and healthy.