Air pollution may be a neglected risk factor for vitamin D deficiency, authors of a study published Wednesday in the Journal of Clinical Endrocrinology and Metobolism say.

According to the Belgian research people living in urban areas — who are exposed to ground air pollution up to three times higher than rural residents — have more than twice the prevalence of vitamin D deficiency as their rural counterparts even if they are consuming the same amount of vitamin D through diet and supplements.

Air pollution filters UVB light, which makes vitamin D.

“The data is already overwhelming, but this is one more piece of work showing that UV light is the body’s natural, intended and most reliable source of vitamin D,” Smart Tan Vice President Joseph Levy said.

In the study, the urban residents and rural residents did not differ in mean ages, body mass indices, and vitamin D intakes, according to the Journal. To read the article click here.