The influence of smoking on vitamin D status and calcium metabolism

Objective: To assess the influence of smoking on serum parathyroid hormone (PTH), serum vitamin D metabolites, serum ionized calcium, serum phosphate, and biochemical markers of bone turnover in a cohort of 510 healthy Danish perimenopausal women. Design: A cross-sectional study. Setting: Copenhagen, Denmark. Subjects: Five-hundred-and-ten healthy women aged 45-58 y, included 3-24 months after last menstrual bleeding. None were using hormone replacement therapy. Methods: The women were grouped according to their current smoking status. The two groups were compared with regard to serum levels of 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25-(OH)(2)D), intact PTH, ionized calcium and phosphate, osteocalcin, as well as urine pyridinolines. Bone mineral density (BMD) was measured with DEXA-scans. Multiple regression analyses were performed to detect the effect of potentially confounding lifestyle factors, such as calcium and vitamin D intakes, alcohol and coffee consumption, sunbathing, and physical exercise. Results: Fifty percent were current smokers. Smokers had significantly reduced levels of serum 25OHD (P = 0.02), 1,25(OH)(2)D (P = 0.001), and PTH (P < 0.001). There was no difference in serum ionized calcium between smelters and non-smokers. We found a negative effect of smoking on serum osteocalcin (P = 0.01), while urinary pyridinolines were similar in the two groups; The small differences in lifestyle between the two groups could not explain these findings. Smokers had small but significant reductions in bone mineral density, Conclusions: Smoking has a significant effect on calcium and vitamin D metabolism, which is not likely to be explained by other confounding lifestyle factors. The depression of the vitamin D-PTH system seen among smokers may represent another potential mechanism for the deleterious effects of smoking on the skeleton, and may contribute to the reported risk of osteoporosis among smokers.