Vitamin D is the vitamin du jour these days, with many doctors urging more sun exposure following years of campaigns advising us to cover up and use sunscreen to prevent skin cancer. Many of us, especially in cloudier areas, don’t get enough of the sunshine vitamin. The elderly and post-menopausal women are more at risk for deficiency, as are those who live in northern climes.

But today comes news that one group seems to be at particular risk, doctors report in the journal Endocrine Practice. Arab-American women who wore the hijab (a Koran-derived dress code that includes a scarf or veil over their hair and modest dress) and didn’t get enough vitamin D through their diet had half the levels of the vitamin of those who didn’t adhere as closely to the dress code. There was no difference in rates of health problems linked to vitamin D deficiency, such as bone or joint pain or breaks, or muscle weakness. The study involved 87 women in Dearborn, Mich., which has a large Arab population.

The more conservatively the women dressed, the lower their vitamin D; those who wore the hijab but ate vitamin D-rich foods such as milk or oily fish had higher levels, though not as high as the women who didn’t adhere to hijab. A measure of 30 nanograms per milliliter of blood is considered sufficient; the most conservatively dressed women in the study had levels as low as 4.5, but even those who didn’t wear the hijab and got some vitamin D in their diets had an average level of 8.5 — "and that's still low," says co-author Raymond Hobbs, a senior staff physician Henry Ford Hospital in Detroit.

"We're not trying to get anyone to take off their hijab," Hobbs tells, but "to do things to prevent problems that might arise" from the tradition. The vitamin was once thought to be necessary only to prevent rickets (soft bones) in childhood and osteoporosis later on, but now, vitamin D deficiency is associated with diabetes, cancer, Crohn's disease, multiple sclerosis, heart disease and infections.

The study isn’t the first to link style of dress to vitamin D deficiency, which affects an estimated 1 billion people around the world. A study published in Pediatrics in 2000 found that ultra-Orthodox Jewish children in Brooklyn who are covered up year-round in long sleeves and dresses were vitamin D deficient. Studies in sunny climes (including Saudi Arabia, the United Arab Emirates, Australia, Turkey, India, and Lebanon) where people may be covered up for religious or other reasons, also found that 30 percent to 50 percent of adults and kids were vitamin D-deficient, according to a 2007 review in the New England Journal of Medicine.

While heavy doses of vitamin D are available in supplements, the body manufacturers the most through sun exposure (admittedly in short supply in early spring in Michigan, when the study was done), Hobbs says. The vitamin naturally occurs in only a few foods, including mackerel, tuna, salmon and eggs, and it's added to milk in the U.S. To get the recommended 1,000 International Units of vitamin D a day (or no more than 2,000), you'd have to drink 20 glasses of milk daily, or eat 80 eggs, Hobbs says. Spend a few minutes in the sunshine, though, and your body will make 10,000 to 20,000 units, he says.

Image by Ranoush via Flickr