The association between serum parathyroid hormone and bone mineral density, and the impact of smoking: the Tromso Study

Objective: To explore the relation between serum parathyroid hormone (PTH) and bone mineral density (BMD), adjusted for lifestyle factors including smoking. Design: Cross-sectional study. Methods: The Tromso Study is a population-based study performed for the fifth time in 2001. Serum PTH was measured and the subjects tilled in a questionnaire covering lifestyle factors. BMD at the hip, distal and ultradistal forearm was measured. Results: Complete datasets were available in 1442 men and 1368 women. Age, body mass index and serum PTH were strong predictors of BMD level at the hip in both genders. No significant relation was seen between serum PTH and BMD at the distal or ultradistal forearm. When smokers and nonsmokers were analysed separately, the relation between PTH and BMD at the hip was significant in current non-smokers only In males, current non-smokers had significantly higher BMD at all three measurement sites compared with current smokers. Male former smokers had values in between current and never smokers. There was a significant and negative relation between number of years smoked and BMD at the hip. In male former smokers, there was an increase in BMD with increasing years since smoking cessation. Conclusion: Serum PTH is negatively associated with BMD at the hip, and the relation seems to be masked, or diminished, by smoking. Smoking reduces BMD at the hip, distal and ultradistal forearm in males, and the effect appears to be mainly time and not dose dependent.