Context: By absorbing sunlight UVB and thereby reducing cutaneous vitamin D photosynthesis, ozone, a common urban pollutant, could cause hypovitaminosis D. Objectives: To establish the characteristics and percentage of subjects with serum 25-hydroxyvitamin-D (25(OH)D)<75 nmol/L among postmenopausal women engaging in outdoor activities either in Brussels or in the countryside. Design/Setting: Cross-sectional study conducted in a university research hospital. Patients/Methods: Among 249 women consulting for either shoulder tendonitis or lumbar spine osteoarthritis, 121 free of conditions and drugs affecting bone and calcium metabolism completed two food-frequency questionnaires within 15 days and we selected the 85 subjects with retest scores within the +/-15% of test scores. Other parameters included sun exposure index (SEI), PTH levels, and femoral neck (FN) T-score. Results: Urban residents (n=38) and rural residents (n=47) did not differ in mean ages, body mass indices and vitamin D intakes. When compared to rural inhabitants, urban inhabitants were exposed to ozone levels 3 times higher, and despite a higher mean SEI (113 versus 87; p<0.001), they had a higher prevalence of 25(OH)D<75 nmol/L (84% versus 38%). After adjusting for SEI, 25(OH)D was 2-fold higher in rural residents, and after adjusting for 25(OH)D, SEI was 3-fold higher in urban residents. FN T-scores correlated positively with 25(OH)D and negatively with PTH levels. Conclusions: Air pollution may be a neglected risk factor for hypovitaminosis D, which is known to compromise several health outcomes. As long as 25(OH)D is >75 nmol/L, calcium intakes>17.5 nmol/day are unnecessary to prevent elevations in PTH levels.