Vitamin D is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body's fatty tissue. Vitamin D helps the body absorb calcium. Calcium and phosphate are two minerals that are essential for normal bone formation. Throughout childhood, your body uses these minerals to produce bones. If you do not get enough calcium, or if your body does not absorb enough calcium from your diet, bone production and bone tissues may suffer. Vitamin D deficiency can lead to osteoporosis in adults or rickets in children.

Celiac disease is a digestive disease that damages the small intestine and interferes with absorption of nutrients from food. People who have celiac disease cannot tolerate gluten, a protein in wheat, rye and barley. Gluten is found mainly in foods but may also be found in everyday products such as medicines, vitamins and lip balms.

Multiple sclerosis (MS) is a chronic, unpredictable disease of the central nervous system (the brain, optic nerves, and spinal cord). It is thought to be an autoimmune disorder. This means the immune system incorrectly attacks the person's healthy tissue.