The good news about vitamin D just keeps getting better. Researchers at the International Agency for Research on Cancer in Lyon, France, recently announced that vitamin D supplementation is linked to lower mortality rates among healthy adults.

The French scientists analyzed the results of 18 separate trials assessing the effects of vitamin D supplementation in more than 57,000 individuals. They found an 8 percent reduction in all-cause mortality among those subjects taking the vitamin for at least three years.

How does extra D boost longevity? The answer may lie in our genes.

Genes are situated on twisted, double-stranded molecules of DNA known as chromosomes. At the ends of the chromosomes are structures called telomeres.

Telomeres have been likened to the plastic tips on shoelaces because they prevent chromosome ends from fraying. This type of damage could scramble DNA and lead to cancer or other serious diseases.

Unfortunately, telomeres aren't indestructible. Each time a cell divides, the telomeres get shorter. When they become too short, the cell can no longer divide. The end result is the deterioration of cells and tissues, accompanied by a higher risk of death.

The findings of a study recently published in the American Journal of Clinical Nutrition suggest that vitamin D may somehow reduce the rate at which telomeres shorten. In a study of more than 2,000 female twins aged 18 to 79, British researchers found that high blood levels of vitamin D corresponded to greater telomere length, protecting the chromosomal structures from the equivalent of five years of aging.

In addition to its apparent anti-aging effects, vitamin D has been shown to deter the growth of cancer, preventing the out-of-control cell division that makes it such a dangerous disease. In humans, higher blood levels of the vitamin have been linked to lower rates of cancer of the prostate, breast and colon.

Researchers at Creighton University recently demonstrated the importance of vitamin D in breast cancer prevention. In a four-year study of more than 1,000 healthy menopausal women, those who took daily doses of calcium plus 1,100 International Units (IU) of vitamin D experienced a 60 percent reduction in breast cancer compared to women taking placebo pills.

Adequate intakes of vitamin D have long been associated with a lower risk of colorectal cancer.

A study conducted by Harvard researchers revealed that men with low blood levels of the vitamin were significantly more likely to develop colon or rectal cancer than those men with higher levels.

The results of several small clinical trials suggest that vitamin D also may thwart the progression of prostate cancer. In men diagnosed with the disease, supplementation was shown to slow the rise in blood levels of prostate specific antigen, a biological marker for the condition.

Vitamin D deficiency appears to contribute to autoimmune disorders, conditions in which the immune system attacks the body. Autoimmune diseases linked to a deficiency of D include type 1 diabetes, rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis.

While much remains to be learned about the role of vitamin D in aging, cancer and autoimmune diseases, scientists have long known that the nutrient is critical to bone health. In the absence of vitamin D, only about 10 to 15 percent of dietary calcium can be absorbed by the body. Higher blood levels of D are associated with greater bone mineral density and a reduced risk of osteoporosis in older adults.

In light of the fact that vitamin D deficiency is relatively widespread in the United States, many experts believe the recommended daily allowance should be increased to at least 800 IU to 1,000 IU. Currently, the recommended daily intake is 200 IU for folks younger than 50, 400 IU for adults 51 to 70 years of age, and 600 IU daily for those 70 and older.

Although some foods, including milk, orange juice and a few grain products are fortified with the vitamin, the amounts they contain are rather low — typically less than 100 IU vitamin D. With about 350 IU per serving, oily fish, including salmon and mackerel, are excellent food sources.

If your eating habits leave something to be desired, there's a good chance that you're not getting enough vitamin D for optimal health. Although there's no substitute for a wholesome, balanced diet, a daily dose of vitamin D could lower your risk for many diseases, and it might even help prolong your life.

Rallie McAllister is a board-certified family physician, speaker and the author of several books, including "Healthy Lunchbox: The Working Mom's Guide to Keeping You and Your Kids Trim." Her website is www.rallieonhealth.com. To find out more about Rallie McAllister, M.D., and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.

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