Vitamin D3 plays a role in many essential bodily functions. Most people obtain adequate levels of vitamin D3 through exposure to the sun's ultraviolet light, but people in northern latitudes, those who wear clothing that covers the entire body, and those who work in occupations that prevent sun exposure are at risk of deficiency. Supplements and dietary sources, such as cod liver oil, fatty fish, egg yolks, fortified orange juice, fortified milk, and ready-to-eat cereals, are effective at preventing deficiency and associated health effects in most cases.
Calcium Absorption and Regulation
Vitamin D3 helps maintain adequate blood calcium levels and is necessary for effective absorption of calcium in the intestines. The Office of Dietary Supplements states that vitamin D3 is important in preventing osteoporosis, rickets and other bone diseases. Without sufficient intake of vitamin D3, the bones will lose density and become weak and prone to fracture.
Cellular Growth and Function
According to the George Mateljan Foundation, vitamin D3 helps maintain healthy cellular development, growth, and function, which may help reduce the risk of certain cancers. By promoting healthy cell growth and activity, the risk of malignant changes to cells is reduced. The vitamin may be especially beneficial at preventing colon, breast and prostate cancers.
Improved Glucose Tolerance
Infants who receive supplemental D3 during their first year of life have a lower rate of type 1 diabetes than infants who consume lower amounts of the vitamin, according to the Mayo Clinic. Moreover, adults taking supplemental vitamin D3 show an improvement in insulin sensitivity. More research is needed into the specific effects of vitamin D3 on the development of type 1 and type 2 diabetes and glucose tolerance.
Immune and Inflammatory Regulation
By regulating immune system activity and decreasing the body's inflammatory response, vitamin D3 may help treat or prevent high blood pressure, autoimmune diseases, multiple sclerosis and irritable bowel disorders.
The George Mateljan Foundation states that certain immune cells in the body, called active T-cells, have vitamin D receptors that help switch off the inflammatory response when vitamin D levels are adequate. This process is directly involved in the progression of many diseases, such as multiple sclerosis, rheumatoid arthritis, and Crohn's disease. In addition, topical vitamin D3 medications, such as the psoriasis drug tacalcitol, are effective at controlling skin cell growth and reducing tissue inflammation, according to the Mayo Clinic.
Toxic Effects of Vitamin D3
When taken in high doses for prolonged periods, vitamin D3 toxicity may occur. The Mayo Clinic warns that too much vitamin D3 may lead to bone loss and hypercalcemia, especially in those with kidney disease, tuberculosis, hyperparathyroidism, sarcoidosis or histoplasmosis.
Symptoms of vitamin D3 toxicity include poor appetite, constipation, nausea, vomiting, weight loss, high blood pressure, weakness, fatigue, headache, dry mouth and kidney dysfunction. According to the Office of Dietary Supplements, vitamin D toxicity typically results from taking too much of the vitamin in supplement form, as dietary sources contain only a small amount of the vitamin and the heat from sun exposure photo-degrades most vitamin D3 before toxic levels are reached.
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