Smoking and bone metabolism in elderly women

Cigarette smoking has been implicated as a risk factor for osteoporosis. In the present study, the relationship between smoking and bone mineral density, calcitropic hormones, calcium absorption, and biochemical indices related to bone and mineral metabolism was examined at baseline, in subjects recruited for an osteoporotic study. The subjects included 489 elderly women, aged 65-77 years. After exclusions (thiazide users), 54 women constituted the smoking group and 390 women were classified as nonsmokers. The effect of frequency of smoking was also examined in this population (33 light smokers [<1 pack/day] and 21 heavy smokers [>1 pack/day]). Adjusted mean total body bone mineral density was 4% lower (0.968 +/- 0.019 vs. 1.009 +/- 0.004) and the total hip density was 6% lower (0.778 +/- 0.024 vs. 0.826 +/- 0.006) in heavy smokers compared with nonsmokers. At the other sites measured (spine, midradius, femoral neck, trochanter, and Ward's triangle), a similar nonsignificant trend was observed. The adjusted mean calcium absorption corrected for weight was lower (13%) both in light and heavy smokers compared with nonsmokers, and serum 25-hydroxyvitamin D was significantly lower (16%) in heavy smokers than nonsmokers. Serum parathryroid hormone (PTH) was higher in heavy smokers, but was not significantly different from that of nonsmokers. A significant increase in bone remodeling markers, serum osteocalcin (4.35 +/- 0.271 vs. 3.79 +/- 0. 066) and urine N-telopeptide/creatinine (NTx/Cr) ratio (74.5 +/- 5. 75 vs. 49.8 +/- 1.4) was seen in heavy smokers compared with nonsmokers. These results suggest that smoking lowers bone mineral density, and is a result of decreased calcium absorption associated with secondary hyperparathyroidism and increased bone resorption.