Vitamin D Abnormalities
The Effects of Deficiency and Toxicity of a Fat-Soluble Vitamin
Jun 20, 2008
Vitamin D, one of the fat-soluble vitamins along with vitamins A, E, and K, is necessary for regulation of calcium in the body. The vitamin is both consumed in food and made by the body, the latter of which involves multiple steps from formation to activation. It can also be problematic when there is too little or too much of the vitamin.
Vitamin D Metabolism
The process of vitamin D formation begins with a molecule called 7-dehydrocholesterol found in the skin. Ultraviolet rays in sunlight convert this molecule into pre-vitamin D. From there, it goes to the liver to be hydroxylated, forming 25-hydroxyvitamin D. This product in turn goes to the kidney to undergo one more hydroxylation reaction and produce 1,25-dihydroxyvitamin D. This is the active form of vitamin D.
Active vitamin D proceeds to raise the blood calcium level in two ways. It stimulates the absorption of calcium from the small intestine and stimulates reabsorption of calcium filtered through the kidneys. In addition, it promotes absorption of calcium by bones in order to strengthen them.
Vitamin D Deficiency
There are many ways to become deficient in vitamin D, most of which involve interference with the normal metabolism of the vitamin. Vitamin D deficiency, in general, can be due to inadequate intake of vitamin D, minimal exposure to sunlight, intestinal diseases that limit absorption of vitamin D from the gut, altered liver function, kidney disease, and resistance to active vitamin D in rare cases. These processes may act alone or on conjunction with one another to reduce vitamin D in the body.
The result is hypocalcemia, a reduction in blood calcium levels. Calcium is an ion necessary for optimal function of muscles and nerves. Symptoms include but are not limited to muscle weakness, muscle pain, muscle spasms, and bone pain due to demineralization of bone to compensate for reduced blood calcium. The treatment is administration of calcium, either orally or intravenously depending on the severity of the deficiency. This is often accompanied with phosphorous supplementation.
Vitamin D Toxicity
Vitamin D toxicity is usually the result of excessive ingestion of the vitamin. The result is hypercalcemia, elevated levels of calcium in the blood. Clinical manifestations include but are not limited to weakness, nausea, vomiting, loss of appetite, and formation of kidney stones. Such patients are treated with cessation of vitamin D supplement intake, intravenous fluids to flush out calcium through the kidneys, and bisphosphonates, if necessary, to inhibit the demineralization of bone.
