The Possible Adventures
"Now that we're seeing the connections to diabetes, heart disease and cancer, are the low D levels increasing [African Americans'] risk for other conditions? We really don't know yet."
— Susan Harris, D.Sc., N87
But what hasn't been shown as clearly, Harris adds, is how this affects health outcomes, because even though African Americans have lower vitamin D levels than Caucasians, they also have lower rates of osteoporosis. The underlying physiological reasons for this are not well understood, and are most likely connected to factors other than vitamin D status.
"There was less interest in vitamin D nutrition in African Americans than there could have been," Harris says, because for a long time, it wasn't seen as having a strong negative impact. "Now that we're seeing the connections to diabetes, heart disease and cancer, are the low D levels increasing their risk for other conditions? We really don't know yet."
With that in mind, Harris has begun work on a three-year study of vitamin D, glucose control and insulin sensitivity in African Americans; the research is funded by a $455,000 grant from the American Diabetes Association. The study will look at whether giving African Americans vitamin D supplements for three months will improve their markers for diabetes risk. The African-American population has a higher incidence of diabetes than Caucasians; among people over age 65, the death rate from diabetes is nearly twice as high.
Let the sun shine?
In general, researchers recommend meeting increased needs for vitamin D through supplements -- unfamiliar words in the nutrition community, where experts usually prefer nutrient-rich foods to pills. But, quite simply, it's almost impossible for most people to eat the volume of vitamin D-rich foods -- whether natural or fortified -- to meet their needs.
"It's not really feasible right now," Dawson-Hughes says. "Foods are fortified at fairly low levels, and there is not a lot of vitamin D, as far as we know, in the natural food supply."
Vitamin D is included in most multivitamins, and also in combination with calcium supplements; in fact, one of the major vitamin manufacturers recently doubled the amount of vitamin D it puts in its "women's formula" multivitamin, from 400 to 800 IUs.
Which raises a thorny question: What about sunlight? Some researchers say 10 minutes of sun exposure to the face and arms at midday, depending on season and location, could be enough to guarantee the body will make enough D.
At the same time, people are cautioned to mind the risks of skin cancer. There's no sure formula for figuring out how much sun exposure might be adequate, but not dangerous, on an individual basis. The 2007 Agency for Healthcare Research and Quality review of vitamin D and bone health states: "We did not find any systematic reviews that addressed the question on the level of sunlight exposure that is sufficient to maintain [vitamin D] concentrations but minimizes risk of melanoma and non-melanoma skin cancer."
The American Academy of Dermatology is emphatic in its advice that people avoid unprotected sun exposure and get their vitamin D from food and supplements, noting that ultraviolet radiation is responsible for more than 1 million skin cancers each year in the United States. Perhaps fearing that people will shun their sunscreen or take to a tanning bed in an effort to get their D, the academy notes that sunscreens are not perfect, and that even those who wear sunscreen will likely absorb some UV rays and produce some vitamin D. On a sunny June day, it could take a fair-skinned individual wearing a typical coating of SPF 15 as little as 20 minutes to get her fill of vitamin D.
That said, in northern-most and southern-most latitudes, "you're still left with almost half the year" when sunlight won't do the job, says Dawson-Hughes. While the body can store vitamin D made during the summer for several months, it's unlikely to be enough to see most people through the winter, Harris says. That process worked much better for prehistoric humans, who spent much more time outside -- and usually died of other causes long before skin cancer could claim them, she says.
Feature by Helene Ragovin, senior writer, Office of Publications
Homepage image by istockphoto
This story ran online on Jan. 12, 2008. It originally appeared in the Fall 2008 issue of Tufts Nutrition.