Vitamin D: Obese and ‘uniform’ risks

Many factors--even Army training--may contribute to high rates of deficiency in this important nutrient.

ANAHEIM Although vitamin D insufficiency has reached what might be considered epidemic proportions, it’s failed to move onto the radar screens of most physicians, much less consumers. A host of new studies now link excess weight with a deficiency in this, the sunshine vitamin. But that wouldn’t explain why female soldiers become increasing D-ficient during basic combat training. For them, an Army study suggests, the problem may trace to what they wear.

The findings emerged this week at Experimental Biology 2010. This umbrella conference, sponsored by the American Society of Nutrition and five other biomedical research societies, also hosted the annual meetings of another 17 guest research societies.

Vitamin D isn’t really a “vitamin” in the classic sense — a nutrient that the body uses to build tissue and perform activities. This so-called vitamin is instead the starting ingredient for a hormone: 1,25-dihydroxy vitamin D. That hormone plays a role in everything from building bone and muscle to fighting infection and risk of diabetes — even autoimmune diseases.

Over the millennia, people have evolved the ability to make ample vitamin D in their skin, at least during most of the year. However, covering up with clothes or sunscreen can block the ultraviolet light needed for skin to stimulate its production. Foods can supply some D, but tend to be a rather anemic source. Not surprisingly, many nutritionists now advocate dietary supplements.

Not that many people avail themselves of much supplemental D — as evidenced by a growing number of studies, many of them presented at this week’s meeting. Most of these measured the form of D that circulates in the body: 25-hydroxy vitamin D. And even in regions where UV exposure remains fairly high year round, like Puerto Rico, people don’t seem to be getting nearly enough of the vitamin.

For instance, Karen Gil and her colleagues at the University of Puerto Rico, in San Juan, found that among the 100 overweight and obese men and women they looked at, 55 percent had sufficient vitamin D — and 29 percent were clearly deficient. Not surprising, given the numbers, some 60 percent of the surveyed individuals were not eating the recommended daily allowance of D (which nearly every nutritionist concedes is woefully in need of revision upward), and many didn’t get much time in the sun.

A drink didn’t hurt
Somdat Mahabir of the National Cancer Institute and his colleagues were investigating the role of alcohol on serum vitamin D values among post-menopausal women. Although alcoholics tend to have weak bones, some data had indicated that moderate alcohol consumption might improve bone mineral density. The question Mahabir’s group sought to answer: Would a drink or two a day compromise bone health?

So they recruited 51 postmenopausal women to a long trial. For eight weeks, each got no alcohol (in orange juice), the equivalent of one drink’s worth, or two drink’s worth of alcohol. Each woman went through each eight week cycle, although in a random order (with four weeks off in between each cycle). During the test phases, all meals were prepared for the women — ensuring that each received all the nutrients needed to support health and maintain her current weight.

Bottom line: This federal study found no link between alcohol and D. Only two things stuck out: Blacks tended to have about two-thirds as much 25-hydroxy vitamin D in their blood as did white women (a trend noted elsewhere in the past). And the more obese a woman was, the lower her vitamin D level. Some studies have indicated that anything under 80 nanomoles of 25-hydroxy vitamin D per liter of blood should be deemed insufficient. In this new NCI trial, lean women tended to average about 60 nm/l, overweight women had around 55 nm/l, and those who were obese averaged only about half the desired level — i.e. roughly 40 nm/l.

Slimming down helps . . .
The good news: A year-long Jenny Craig-sponsored study of weight loss in roughly 400 women in their mid-40s found that as these ladies shed the pounds, their vitamin D values climbed. Which was a good thing since their starting (and, unfortunately, ending) vitamin D levels would qualify them as deficient.

Still, women who dropped 10 percent of their body weight increased 25-hydroxy vitamin D values by about 9 percent, reports Cheryl Rock of the University of California, San Diego, and her colleagues. One possible confounder they couldn’t exclude: As women slimmed down, they might have spent more time exercising outdoors — soaking up some rays. And making extra vitamin D.

. . . unless you’re wearing combat fatigues
Presumably, the 74 female Army soldiers undergoing basic combat training at Fort Jackson in Columbia, S.C., between August and October got plenty of sun — and exercise. Still, during eight weeks of intense drills and training, their 25-hydroxy vitamin D dropped by an average of 13 nm/l. Which is bad news, since nearly 60 percent of these young women entered basic training below 75 nm/l. By the end of their training, 75 percent fell into this category.

Drops varied by ethnicity. Blacks started low — about 46 nm/l — and stayed there. Almost exactly. Hispanic whites started out averaging 74 nm/ml and non-Hispanic whites started at nearly 90 nm/l. Vitamin D values in both of these groups dropped 16 percent during training.

Although it’s impossible to know precisely what contributed to the decline in their circulating vitamin D levels, Nancy Andersen of the U.S. Army Research Institute of Environmental Medicine in Natick, Mass., and her colleagues speculate it was the uniforms these women had to wear — and a diet that didn’t provide much vitamin D.

There may be an important lesson here for the military, the authors say. They point out that risk of stress fractures — one of the most debilitating injuries in recruits — has been linked to low vitamin D. “And attrition rate from basic combat training in female soldiers with a diagnosis of stress fracture is 60 percent,” they add.

Want to retain recruits, keep their bones healthy. And what helps a 21-year-old female recruit will help the rest of us as well. We all need to bone up on plenty of D, and the plumper and more darkly skinned among us may need to work especially hard at fighting D-ficiency.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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