Smoking increases bone loss and decreases intestinal calcium absorption

Cigarette use is a risk factor for increased bone mineral density (BMD) los s but the mechanisms are not well understood. The relationship of smoking t o rates of BMD change at the femoral neck, spine, and total body, and to in testinal calcium absorption were examined in 402 elderly men and women (32 smokers, 370 nonsmokers) who participated in a 3-year placebo-controlled st udy of calcium and vitamin D supplementation. Subjects in the supplemented group took 500 mg/day of elemental calcium and 700 IU/day of cholecalcifero l. 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) we re 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 differen ce 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 abso rption fraction was lower in smokers (12.9 +/- 0.8%, n = 23) than nonsmoker s (14.6 +/- 0.2%, n = 310,p < 0.05) after adjustment for gender, age, suppl ementation status, and dietary calcium and vitamin D intakes. Smokers of at least 20 cigarettes per day (n = 15) had the lowest mean absorption fracti on (12.1 +/- 1.1%). With calcium and vitamin D supplementation, the proport ionate increase in urinary calcium/creatinine excretion was lower in smoker s (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 contribu ting factor.