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Children living in areas of high pollution are at risk of developing vitamin D deficiency rickets and should be offered vitamin D supplements. The most important source of vitamin D is that produced in the skin after exposure to ultraviolet B (UVB) sunlight, and there is increasing concern that smog created by industrial and vehicular emissions absorbs UVB photons, thus reducing the cutaneous vitamin D synthesis. Researchers recruited a total of 57 children from Delhi, India, who lived in two areas of the city with disparate pollution levels, and hypothesised that serum total 25-hydroxycholecalciferol (25(OH)D)—a reliable measure of vitamin D status—would be lower in those from the heavily polluted area. They were right: mean 25(OH)D of children in the more polluted area was 12.4 (7) ng/ml, compared with 27.1 (7) ng/ml in children in the less polluted area. The authors also measured the amount of UVB sunlight to reach the ground in both areas and found that significantly more did so in the less polluted area. The …