Two studies cite need for more Vitamin D

Two unrelated research reports yesterday added to a growing pile of evidence on the importance of Vitamin D while offering little guidance on how much extra to take, if any.

A study of 6,824 British subjects, nearly all of them white and every one born during a single week in March 1958, found an association between very low blood levels of Vitamin D and chronic widespread pain in women but not in men. The link was apparent even after the numbers were statistically adjusted to account for a series of known risk factors, from low physical activity to high body mass index, the authors write in the online edition of Annals of the Rheumatic Diseases.

In the other report, researchers tracked 13,331 American adults ages 20 and older whose Vitamin D levels were recorded as part of a national survey between 1988 and 1994. Their analysis, published in the Archives of Internal Medicine, found that people whose Vitamin D levels at the time of the physical fell into the sample's lowest quartile were 26 percent more likely to die from all causes over the following nine years than were those in the highest quartile.

Low Vitamin D levels had previously been linked to diabetes, hypertension and several cancers; this is believed to be the first study to examine mortality in the general population.

And although the effect was seen in both men and women, it was more pronounced in women in this study, too - possibly, the authors speculated, because of a hormone interaction between estrogen levels and Vitamin D. Authors of both studies also cautioned that very high blood levels of the vitamin could increase the risk.

With surveys finding that perhaps half of all Americans have less-than-optimal levels of Vitamin D - though nowhere near as low as what was defined as deficient in these two studies - some physicians recommend that patients routinely get simple 25(OH)D tests, which measure blood levels of 25-hydroxyvitamin D. They should then discuss the results.

Erin Michos, co-lead investigator on the mortality study and an assistant professor at the Johns Hopkins University School of Medicine's Heart and Vascular Institute, recommends that people boost their Vitamin D levels by consuming dairy products (such as milk) that are fortified with Vitamin D, eating diets rich in fish such as sardines and mackerel (or taking cod-liver oil supplements), and getting 10 to 15 minutes of daily exposure to the sun, particularly in winter.

If vitamin supplements are used, Michos says, there is no evidence of benefits from more than 2,000 international units per day. The U.S. Institute of Medicine suggests that an adequate daily intake of Vitamin D is between 200 and 400 IU, leading to blood levels close to 30 ng/ml (nanograms per milliliter), which it considers optimal.