Vitamin D can be created by the body when the skin is exposed to sunshine for a small amount of time. Certain factors such as amount of melatonin, lack of sunshine and certain lifestyles can diminish Vitamin D stored within the body. A lack of Vitamin D can be lethargy, tiredness, muscle problems, bone pains and mood changes. Certain health problems such as weak immune system may be assisted by Vitamin D. Supplementation with Vitamin D alongside a healthy diet can contribute to the normal absorption and utilization of calcium and phosphorus (which contribute to normal bones and normal teeth). Vitamin D is also used within the body for the normal function of the immune system. Vitamin D also contributes to normal blood Calcium levels and has a role in cell division.