Smoking as an effect modifier of the association of calcium intake with bone mineral density

Data from physiological studies suggest smoking to have detrimental effects on calcium absorption, but large-scale investigations of this interaction and its importance with respect to bone health in humans are lacking.

The objective of the study was to examine the potential smoking-associated effect heterogeneity in the relationship of dietary calcium intake with bone mineral density in the general population.

This was an observational, cross-sectional study.

A total of 14 116 participants of the Third National Health and Nutrition Examination Survey, including 6882 never, 3532 former, and 3702 current smokers. The median age of the participants was 44 years, and 52% were female.

Bone mineral density at the femoral neck as determined by dual-energy x-ray absorptiometry was measured.

In multiple linear regression adjusting for age, sex, race/ethnicity, and education, the association of calcium intake with bone mineral density was characterized by suggestive overall positive trends in all three smoking behavior categories. Detailed dose-response analyses by restricted cubic spline modeling revealed more pronounced nonlinearity among former smokers, but the interaction of smoking with calcium intake on bone mineral density did not reach statistical significance in any of these models. The dose-response curves became even more homogenous across smoking behavior strata after additional adjustment for body mass index and physical activity.

Even though the present results cannot rule out that smoking-associated differences in calcium absorption exist, they do suggest that smoking behavior does not have any relevant impact on the beneficial effects of calcium intake on bone mineral density at the population level.