“Results show clear differences in vitamin D status between the north and south and marked ethnic differences,” said researchers from Aberdeen University in Scotland.
The body produces vitamin D upon exposure to the UV-B radiation found in sunlight, with a light-skinned person able to synthesize all they need in as little as 15 minutes during the summer at a moderate latitude. Because the sun gets weaker the farther a person moves from the equator, however, it takes more and more sun exposure to get the same amount of the vitamin. This problem is only exacerbated in the winter.
The researchers compared both sun exposure and vitamin D levels in women under the age of 66 living in either Aberdeen, in the north of Scotland, or in Surrey, in England’s south. All the women wore UV-B sensitive bandages on their bodies, and their vitamin D blood levels were measured once every three months over a 15-month period.
The researchers found significantly lower sun exposure in Aberdeen than in Surrey at all times of the year. Mirroring these results, they found no vitamin D deficiency among any white Surrey residents. In contrast, between 25 and 27 percent of Aberdeen women were vitamin D deficient during the winter or spring, while 4.2 percent were deficient even in the summer.
Even in Surrey, as many as 60 percent of Asian women were still vitamin D deficient, and also showed lower sun exposure than their white counterparts. The researchers suggested that more traditional clothing (which covers more of the skin) and darker skin might account for part of this difference.
People with darker skin produce vitamin D more slowly than people with lighter skin.
“The recommendation of 10 minutes of sunlight exposure a day may need to be changed for those with darker skin or in higher latitudes,” researcher Helen Macdonald said.