Q: I've seen a number of articles recently suggesting that vitamin D protects against cancer. What do you think?-- AnonymousA: Vitamin D has been getting a lot of press lately as more and more studies link it with reduced rates of a number of types of cancer (18 at last count) as well as with lower risks of autoimmune diseases, including multiple sclerosis and rheumatoid arthritis. Some experts estimate that thousands of cancer deaths could be avoided in the United States each year if everyone got enough vitamin D.
The connections between vitamin D, cancer and other diseases stem from observations that certain disorders, including some forms of cancer, occur much less frequently in areas with sunny warm climates than they do in places where the sun doesn't shine brightly throughout the year. For example, in 1980 a team of epidemiologists found that rates of colon cancer were much higher in populations that were exposed to the least amount of light (especially in major cities and in high-latitude rural areas).
Bear in mind that our bodies make vitamin D in response to exposure to the ultraviolet B rays of the sun ("B" lightwaves are medium-length, as opposed to the long "A" waves). If you live in an area where the sun isn't strong year round or if you rarely venture outside or always put on sunscreen when you do, you could be shortchanged on vitamin D unless you take supplements.
It isn't easy to get enough from your diet. The best sources are fortified milk and cereals, eggs, salmon, tuna, mackerel and sardines. (Unfortunately, most fortified foods provide vitamin D2, a form which is much less well utilized by the body than D3.)
Recent research has suggested that vitamin D regulates cell proliferation and can hold in check the sort of wild cell growth that leads to cancer. A number of studies have shown that some cancer patients diagnosed in the summer or fall when vitamin D levels are high as a result of sun exposure have higher survival rates than patients diagnosed in the winter.
We've long known that multiple sclerosis is rare at the equator and becomes much more frequent at high latitudes. Researchers from the Harvard School of Public Health in Boston who followed a group of more than 185,000 nurses for 19 years, getting updated nutritional information from them every four years, found that those with the highest intake of supplemental vitamin D had a 40 percent lower risk of developing MS compared to women who didn't take supplements. The study was published in the January 13, 2004, issue of the journal Neurology. In Iowa, researchers who followed a group of more than 29,000 women for more than 11 years found that those with the highest intake of vitamin D had the lowest risk of rheumatoid arthritis. Here, vitamin D may be protective via effects on the immune system.
This is a fascinating and fast-growing area of research. As you may know, in 2005 I raised my vitamin D recommendation from 400 IU daily to 1,000 IU because of the accumulating body of evidence showing that vitamin D is more important than we once thought, not only for our bones (it promotes calcium absorption) but for the protection it provides against many serious diseases. Most experts now agree that 1,000 IU is the amount of vitamin D we all should be getting daily. Look for supplements that provide D3 (choleciferol) rather than D2 (ergocalciferol). And there is no concern about toxicity at this dose even though vitamin D is fat soluble. In fact, as more evidence about the benefits of vitamin D are forthcoming, some researchers are already suggesting that 2,000 IUs is a more sensible dose. Stay tuned.
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