Inclusion of tobacco exposure as a predictive factor for decreased bone mineral content

Tobacco exposure has been implicated as a risk factor for decreased bone density, which might result in osteoporosis. Cotinine, a metabolite of nicotine, is commonly used as a marker for tobacco exposure (active or passive). The objective of the present study was to compare tobacco exposure with other predictive factors for low bone mineral content (BMC), as determined by dual photon bone absorptiometry (DXA) in a national U.S. sample. Publicly available interview and clinical examination data from the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES-III) were used. Our data included 14,060 subjects from 19,528 randomly selected representative U.S. households. Clinical laboratory data included serum values for calcium and cotinine. BMC was assessed radiologically by DXA at five proximal femur sites. BMC values were adjusted for age, as well as height, weight, and bone area to correct for bone and body size. We used t tests to compare continuous variables and chi-square tests to explore associations between categorical variables. Multivariate regression models were developed for each gender with appropriate covariates. Intertrochanter BMC explained the most variation (highest R-2) and was selected as the basis of the comparison. Serum cotinine had a significant inverse relationship to BMC in both males (p=.0069) and females (p=.0063). Serum cotinine, as a marker for tobacco exposure, is a statistically significant risk factor for decreased BMC in both genders and should be included in multivariate regression models to predict low BMC.