Smoking increases bone loss and decreases intestinal calcium absorption

Cigarette use is a risk factor for increased bone mineral density (BMD) loss but the mechanisms are not well understood. The relationship of smoking to rates of BMD change at the femoral neck, spine, and total body, and to intestinal calcium absorption were examined in 402 elderly men and women (32 smokers, 370 nonsmokers) who participated in a 3-year placebo-controlled study of calcium and vitamin D supplementation. Subjects in the supplemented group took 500 mg/day of elemental calcium and 700 IU/day of cholecalciferol. Two-hour calcium absorption fraction was determined three times, at 18, 30, and 36 months, with a single isotope method utilizing Ca-45 in a subset of 333 subjects. Annualized rates of BMD loss (adjusted for baseline BMD, weight, age, gender, supplementation status, and dietary calcium intake) were higher in smokers than nonsmokers at the femoral neck (-0.714 +/- 0.285 %/year vs. +0.038 +/- 0.084 %/year, p < 0.02), and total body (-0.360 +/- 0.101 %/year vs. -0.152 +/- 0.030 %/year, p < 0.05). No significant difference was observed at the spine (+0.260 +/- 0.252 %/year in smokers vs. +0.593 +/- 0.074 %/year in nonsmokers, p = 0.21). The mean (+/- SEM) calcium absorption fraction was lower in smokers (12.9 +/- 0.8%, n = 23) than nonsmokers (14.6 +/- 0.2%, n = 310,p < 0.05) after adjustment for gender, age, supplementation status, and dietary calcium and vitamin D intakes. Smokers of at least 20 cigarettes per day (n = 15) had the lowest mean absorption fraction (12.1 +/- 1.1%). With calcium and vitamin D supplementation, the proportionate increase in urinary calcium/creatinine excretion was lower in smokers (44 +/- 12%) than nonsmokers (79 +/- 9%, p < 0.05). These results suggest that smoking accelerates bone loss from the femoral neck and total body in the elderly and that less efficient calcium absorption may be one contributing factor.