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

Parathyroid hormone (PTH) is the main regulator of calcium homeostasis, and plays an important role in regulation of bone mass. Decreased bone mineral density (BMD) has been shown in subjects with primary and secondary hypoparathyroidism. Previous epidemiological studies showing conflicting results in subjects with primary and secondary hypothyroidism have failed to adjust for smoking. This is important as even moderate smoking can cause a decrease in serum parathyroid hormone levels. In a cross-sectional study by Sneve et al., serum PTH and BMD were measured and a questionnaire completed covering lifestyle factors including smoking status and alcohol consumption. The paper reports on the fifth Tromsø Study, a population based study from which complete datasets, comprising of two questionnaires, x-ray absorptiometry of the hip and forearm, and serum PTH measured from non-fasting subjects, were available in 2810 subjects (1442 males and 1368 females). Statistically significant relationships between BMD and serum PTH levels, age, and body mass index were found at the hip. BMD at the hip, distal and ultradistal forearm was found to be significantly higher in male current non-smokers than in smokers, when adjusted for age and other factors. In former smokers of both genders there was a significant negative relationship between BMD at the hip and the number of years smoked. Male subjects showed a positive relationship between BMD and the number of years since cessation of smoking. This study, to the authors’ knowledge, represents the largest known population-based study into serum PTH and BMD. The authors concluded that PTH is a significant negative predictor of BMD at the hip in both genders and the effect of smoking was found to be time rather than dose dependent, and more pronounced in men. Sneve, M., Emaus, N., Joakimsen, R.M., Jorde, R. European Journal of Endocrinology, 158, 401-409. DOI: 10.1530/EJE-07-0610