Vitamin D, commonly referred to as the sunshine vitamin, helps the body maintain normal levels of calcium and phosphorus in the blood. Vitamin D facilitates absorption of calcium in the body to form and maintain strong bones. Recent research suggests vitamin D may also provide protection from a growing list of chronic diseases including hypertension and several auto-immune diseases. Other roles vitamin D plays in the body is currently under investigation:

• Muscle strength: vitamin D improves balance and muscle performance thereby reducing the risk of falling.

• Osteoarthritis: vitamin D's anti-inflammatory effects on cartilage look promising.

• Gum disease: vitamin D suppresses inflammation that causes periodontal disease.

• Cancer: vitamin D hinders growth of new blood vessels that feed tumors.

• Insulin & Diabetes: preliminary evidence shows that vitamin D may positively influence resistance to insulin.

The term "Vitamin D" refers to several different forms of this nutrient. Two forms of vitamin D, important for humans, are: ergocalciferol (vitamin D2) synthesized by plants, and cholecalciferol (vitamin D3) synthesized by human skin when exposed to ultraviolet-B (UVB) rays, or consumed in one's diet.

Ergosterol is the basic building block of vitamin D in plants. When ultraviolet light from the sun hits the leaf of a plant, ergosterol is converted into ergocalciferol, or vitamin D2.

Cholesterol is the basic building block of vitamin D in humans. When UVB rays from sunlight reaches our skin cells, cholesterol is converted into cholecalciferol, or vitamin D3.

Both of these substances, ergocalciferol and cholecalciferol, are usually referred to as "pro-vitamin D". They are carried by the bloodstream to the liver, then the kidneys, as they are converted into fully active vitamin D, called calcitriol.

Who Needs Vitamin D and How Much?

The U.S. RDA/RDV for vitamin D is 400 IU. Most experts agree the current recommended intake is too low. Taking supplements of vitamin D, with or without calcium, increases the density of some bones including the hip. However, for vitamin D to help strengthen bones, it must be consumed in high enough doses.

Unless you're exposed to sunshine regularly, take a supplement. Plan to consume 1,000 IU of vitamin D a day. Vitamin D is usually included in multivitamins and is added to most calcium supplements. There is very little risk of overdose. It's safe to take well over 2,000 IU daily. Food sources of vitamin D include:

Lisa Tsakos