News Stories in Perspective

Vitamin D: Play It Smart While Watching & Waiting

A growing number of researchers are calling for a re-evaluation of long-standing recommendations regarding our vitamin D needs. Some current proposals would require many people to rely on supplements or fortified foods to attain the higher targets. It’s a bit early in the debate for the public to fully embrace a universal jump in dosage (some experts note potential risks), but the spotlight shining on the “sunshine vitamin” can remind us to make sure we at least meet the current standards.

Vitamin D is regarded as essential to bone health, but also shows potential cancer fighting effects, according to emerging research. In laboratory studies, vitamin D promotes the development of “normal” cells, controlling growth and prompting self-destruction of cancer cells.

We produce vitamin D in our skin in response to sunlight and we also get the vitamin from our food. Fortified milk is a major source of vitamin D in the U.S.

A study published in 2007 linked early exposure to vitamin D with reduced breast cancer later in life. Among more than 2000 women (almost half recently diagnosed with breast cancer) those subjects who reported more sun exposure or most milk consumption during adolescence were about a third less likely to have breast cancer compared to those with lowest levels of exposure. Abundance of either source of the vitamin later in life showed little or no protection.

Similarly, another recent study, which involved more than 30,000 participants, found that premenopausal women who consumed the most vitamin D were 35 percent less likely to develop breast cancer over a 10-year period compared to women who consumed the least. Again, vitamin D intake of post-menopausal women showed no breast cancer link.

Since both diet and sun exposure affect vitamin D status, researchers say it may be best to study the relationship of blood levels of vitamin D to health. In a recent study of more than 2700 women, compared to those with the lowest blood levels – including levels within the current “normal” range – women with higher levels showed 43 to 59 percent lower breast cancer risk. In an analysis of two earlier studies, those with highest blood levels had up to a 50 percent drop in breast cancer risk.

A 2007 study in the Journal of the National Cancer Institute showed no connection between blood levels of vitamin D and total cancer deaths. Yet highest blood levels of vitamin D were linked to a 72 percent drop in colon cancer deaths. Likewise, in an analysis of five earlier studies, those with highest blood levels of vitamin D showed 50 percent less incidence of colon cancer.

Some researchers say that studies like these should be enough to prompt the Institute of Medicine (IOM) to raise vitamin D recommendations – paving the way for greater food fortification or higher amounts of the vitamin in multivitamins. Yet questions remain about whether benefits vary with life stage or genetic differences. Some researchers question whether high supplementation could impair immune function and actually increase cancer risk.

Current government standards define adequate vitamin D intake (total of food and any supplements) as 200 IU (International Units) for adults younger than 50 years, 400 IU for those between the ages of 50 and 70, and 600 IU for those 71 years and older. The safe upper intake level is set at 2,000 IU.

Two 8-ounce glasses of fortified milk provide about 200 international units (IU) of vitamin D and 3-ounces of cooked salmon provide about 360 IU. Egg yolks and several other varieties of wild fatty fish are also sources of the vitamin.

Most older people need some fortified foods or a supplement to reach the existing recommendations. While the D debate continues among the experts, however, other adults can choose whether they’d rather aim for the current minimum standard, or combine dairy, fortified foods and supplements to reach higher levels (staying, of course, within the 2000 IU limit).