The D vitamins are fat-soluble vitamins that occur naturally in very few foods, such as salmon and tuna. Some foods are fortified with vitamin D, and the substance is available as a dietary supplement. The body also synthesizes vitamin D from sunlight. Vitamin D3 is the form important for humans, and vitamin D2 is the synthetic form of D3.
Bone Health
Vitamin D is essential for calcium absorption and for maintaining adequate calcium and phosphate levels in the blood, according to the U.S. National Institutes of Health (NIH). This allows normal bone mineralization and bone growth. Along with calcium, vitamin D protects against loss of bone density (osteoporosis), a condition common in older adults that results in thin and brittle bones. Adequate intake or synthesis of vitamin D is necessary for preventing bone softening, called rickets in children and osteomalacia in adults.
Neuromuscular Function
Vitamin D3 is important for neuromuscular function. A review of current knowledge published in Osteoporosis International in March 2002 found that vitamin D deficiency in elderly people was associated with increased body sway and decreased muscle strength. Changes in gait, difficulty getting up from a seated position, inability to climb stairs and muscle pain can occur due to vitamin D deficiency. The Linus Pauling Institute (LPI) at Oregon State University cites a study of nursing home residents with an average age of 89 years in which those taking 800 international units (IU) a day of supplemental vitamin D had a 72 percent lower rate of falling than those taking a placebo. Vitamin D deficiency causes muscle weakness and pain not only in elderly people, but in other adults and in children as well, according to the LPI.
Cancer Prevention
Vitamin D inhibits proliferation (rapid division) of cells and stimulates the differentiation of cells. Differentiation involves the specialization of cells for specific functions and generally reduces proliferation. Uncontrolled proliferation of cells may lead to cancer.
Immune System and Inflammation
Vitamin D may enhance the immune system while also stopping the development of autoimmune disorders, according to the LPI. Additionally, nutritional science research at the University of Missouri has found that vitamin D deficiency is linked to inflammation, a negative immune system response, in healthy women. Vitamin D3 shows benefits in preventing and treating inflammatory diseases such as heart disease, and disorders with both inflammatory and autoimmune factors, such as multiple sclerosis and rheumatoid arthritis.
Cardiovascular Benefits
Sufficient vitamin D levels may be important for lowering the risk of high blood pressure, as explained by the LPI. Additionally, research at the Heart Institute at Intermountain Medical Center indicates that insufficient levels of vitamin D may significantly increase the risk of stroke, heart disease, heart failure and death, even among people with no history of heart disease.
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