Several studies have suggested that vitamin D deficiency contributes to cardiovascular disease, cancer,  obesity and diabetes and death, according to background information in the article. The optimum blood level of 25-hydroxyvitamin D (25[OH]D) has been suggested to be 30 nanograms per milliliter or higher. Approximately 41 percent of U.S. men and 53 percent of U.S. women have levels lower than 28 nanograms per milliliter.

Michal L. Melamed, M.D., M.H.S., of the Albert Einstein College of Medicine, Bronx, N.Y., and colleagues analyzed vitamin D levels in 13,331 individuals who participated in the Third National Health and Nutritional Examination Survey (NHANES III), conducted by the Centers for Disease Control and Prevention. Vitamin D levels were collected between 1988 and 1994, and participants were tracked through 2000.

Over a median (midpoint) of 8.7 years of follow-up, 1,806 of the participants died. When they were divided into four groups (quartiles) based on their vitamin D levels, those in the group with the lowest level (less than 17.8 nanograms per milliliter) had a 26 percent increased rate of death from any cause compared with those in the group with the highest vitamin D levels. No significant associations were found when the researchers assessed vitamin D levels and risk of death from cardiovascular disease or cancer alone.

Low vitamin D levels may be associated with death through their effect on blood pressure, the body’s ability to respond to insulin, obesity and diabetes risk, the authors note. Several lines of evidence support vitamin D’s role in death risk, including the fact that cardiovascular events are more common in the winter, when vitamin D levels are lower, and that cancer survival is better if the disease is diagnosed in the summer when levels are higher.

“In conclusion, the lowest 25(OH)D quartile (less than 17.8 nanograms per milliliter) is associated with a higher risk of all-cause mortality in the general U.S. population,” the authors conclude. “Further observational studies are needed to confirm these findings and establish the mechanisms underlying these observations. If confirmed, randomized clinical trials will be needed to determine whether vitamin D supplementation at higher doses could have any potential benefit in reducing future mortality risk in those with 25(OH)D deficiency.” (Arch Intern Med. 2008;168[15]:1629-1637.)

Editor’s Note: Dr. Melamed and this analysis and co-author Dr. Michos were supported by grants from the National Institutes of Health. Dr. Michos is also supported by the P.J. Schafer Cardiovascular Research Fund. Co-author Dr. Post is supported in part by the Paul Beeson Physician Faculty Scholars in Aging Program. Dr. Michos has received consulting fees from Abbott Pharmaceuticals. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. Vitamin D can also be produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis and as such is said to be a preventative mechanism for some forms of skin cancer.

Not all forms of vitamin D are created equal. Some forms are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form.

Vitamin D is essential for promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and prevent hypocalcemic tetany. Vitamin D is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.

Vitamin D has other roles in human health, including modulation of neuromuscular and immune function and reduction of inflammation. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D.

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. Unlike many other nutrients, there is insufficient evidence to establish an RDA for vitamin D. Instead, an Adequate Intake (AI) -- a level of intake sufficient to maintain healthy blood levels of an active form of vitamin D -- has been established. The 1998 AIs for vitamin D for adults are the same in males and females, but increase with age.
    * Ages 19-50: 200 International Units (IU)
    * Ages 51-69: 400 IU
    * Age 70 and older: 600 IU

Deficiencies may result in several undesirable health effects:

• Vitamin D deficiencies can increase your risk for