Zoltan Rona - Vitamin D: The Sunshine Vitamin

Vitamin D Basics Vitamin D is not your typical vitamin. First, vitamin D (also called the sunshine vitamin) is created under the skin by ultraviolet light. We usually get vitamins from the foods we eat; however, in the case of vitamin D, there simply are not enough rich food sources for people to get adequate amounts in their diet. To get sufficient vitamin D, we need to be exposed to sunshine or use supplements.

Second, unlike other vitamins, vitamin D is turned into a hormone in the body. This biochemically active form of vitamin D is closely related structurally to two other hormones, cortisone and estrogen.

The body has a huge need for vitamin D. All cells, tissues, and organs in the human body have vitamin D receptors, basically meaning that they await the arrival of the vitamin (or hormone) to perform various vital functions.

The most basic and best-known role of vitamin D is to regulate calcium and phosphorus metabolism; that is, vitamin D tells calcium and phosphorus where to go and what to do. Working with the parathyroid glands located in the neck, vitamin D helps the gut absorb calcium and helps to balance calcium with phosphorus in the arteries, bones, kidneys, and teeth. If calcium and phosphorus intakes are adequate and vitamin D is deficient, major problems can arise in numerous tissues and organs, leading to diseases such as atherosclerosis, blood-clotting disorders, kidney stones, osteoporosis, and at least thirty-six other diseases.

When vitamin D levels in the blood are low, both calcium and phosphorus levels decrease, causing parathormone to be released from the parathyroid glands. This, in turn, causes the bones to release calcium and phosphorus to maintain a steady state of these two minerals in the blood. When vitamin D levels in the blood are sufficient, the hormone calcitonin causes excess calcium and phosphorus to be returned to the bones. Vitamin D works to orchestrate this complex phenomenon, and sufficient levels are crucial for bone health.

Without adequate amounts of vitamin D, bones lose minerals and even mass. Low levels of calcium also affect the nervous system and the cardiovascular system. In addition, it is now known that vitamin D controls several adrenal gland hormones, the speed at which cells grow, the production of enzymes, and the function of some of our genes.

VITAMIN D IN THE HUMAN BODY

Without sunshine or a source of ultraviolet lightor in people with very dark skinvitamin D production is significantly impaired. Vitamin D3 (cholecalciferol) is actually manufactured in the skin when ultraviolet light, either from the sun or a tanning bed, interacts with the enzyme 7-dehydrocholesterol to form it. Then the liver and kidneys take over, converting vitamin D3 into the major circulating, active forms of vitamin D called 25-hydroxy cholecalciferol and 1,25-dihydroxy cholecalciferol.

If vitamin D is ingested from either an animal or plant source (it exists in only minute amounts in the plant kingdom), it is absorbed through the walls of the small intestine with the aid of bile coming from the gallbladder (or the liver, in those people without gallbladders). Some conditions such as food allergies can bind vitamin D and prevent its absorption from the gut.