by Uma Shankari

Created on: October 12, 2009

Vitamin D deficiency is a growing epidemic across the world and is a causative factor for several debilitating diseases.

Strictly speaking, vitamin D is not a vitamin at all, because with moderate exposure to ultraviolet radiation from the sun, we do not need to get it from food. Living in high latitudes, indoor living, darker skin pigmentation, and use of sunscreen can cause vitamin D deficiency. Breast-fed babies can be deficient in vitamin D as mother's milk doesn't contain adequate vitamin D, a condition made worse if the mother is already low on the vitamin.

Vitamin D is considered a prohormone, a precursor to a hormone. Vitamin D is an essential part of the endocrine system as it controls the growth and differentiation of cells, the synthesis of key enzymes, several of the adrenal hormones and appears to have other direct DNA functions and even be involved in DNA repair.

When ultraviolet rays from the sun strike the skin of our bodies, the skin cells in our body called keratinocytes trigger vitamin D synthesis. The endogenously made as well as vitamin D obtained from food are biologically inert (called vitamin D3). D3 is the major circulating form of Vitamin D and is what gets measured in the lab tests. D3 must be metabolized further in the liver and in the kidney to yield activated forms of D called calcidiol and calcitriol, respectively. It is this activated form that can form calcium-binding protein needed for the absorption of calcium from the intestines.

Vitamin D and Calcium Metabolism

Vitamin D facilitates the absorption of calcium and phosphate in the intestines. Calcium's absorption from the gut is important to preserve homeostasis and for the maintenance of many physiological systems.

Vitamin D, calcium, and parathyroid hormone coordinate in a tightly regulated system. Parathyroid glands in the body regulate the calcium level in our bodies within a very narrow range (by withdrawing or depositing calcium on the bones) so that the nervous and muscular systems can function properly. If your body does not have sufficient calcium, it will start producing parathyroid hormone (PTH). PTH causes your body to take calcium and phosphorous from your bones. Insufficient vitamin D will weaken both your bones and teeth.

Without sufficient vitamin D, bones can become thin, brittle, or misshapen. The growth of children deficient in vitamin D may become retarded; in addition to being subjected to skeletal deformities, they run the risk of hip fracture later in life.

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