Vitamin D is an important chemical in the body that keeps bones strong by helping to transport calcium from digested food in the stomach to the blood stream. There are two ways the body gets Vitamin D: 1) Exposure to UV Radiation and 2) Ingesting foods or supplements that contain Vitamin D.
Some studies have asserted that practicing safe sun habits can lead to a Vitamin D deficiency which in turn can increase your risk for certain cancers and other diseases such as Multiple Sclerosis, Rheumatoid Arthritis, Juvenile Diabetes, Parkinson's and Alzheimer's. Because UV Radiation stimulates the body to manufacture Vitamin D also known as "the sunshine vitamin" some scientists have suggested that people regularly visit tanning salons and dose themselves with UV Rays, however overexposure to UV can actually weaken your immune system reducing your defense against infection and disease.
For most people the RDA (recommended daily allowance) of Vitamin D can be easily met by eating D-Rich Foods such as fatty fish (Salmon, Tuna, Sardines, Mackerel, Eel, etc.), eggs, beef liver, mushrooms and D-fortified dairy products or by taking a regular dietary supplement of 2000 IU per day during the summer and 5000 IU per day during the winter time - Research has shown that adequate Vitamin-D may also be associated with healthy hair follicle growth cycles.