Fat mass is an important predictor of parathyroid hormone levels in postmenopausal women

Abstract

Previously, we reported that people with elevated parathyroid hormone (PTH) levels due to primary hyperparathyroidism have increased body weight compared to eucalcemic controls. We sought to determine whether the same relationship between PTH and body weight exists in eucalcemic healthy postmenopausal women, and to investigate the relationships between components of body weight, PTH, vitamin D metabolites, and metabolic indices. We performed a cross-sectional analysis of 116 healthy community-dwelling postmenopausal women. Pearson correlation analysis was used to test for univariate linear relationships between variables, and stepwise multiple regression analysis to assess for multivariate relationships. We found that PTH was significantly positively correlated with body weight, regional and total fat mass, and percent body fat, and negatively correlated with activity levels, 25 hydroxyvitamin D (25OHD), dietary calcium intake, and serum phosphate. On multivariate analysis, PTH was positively related to percent body fat (P = 0.020; partial r2 = 0.10) and negatively related to dietary calcium intake (P = 0.041; partial r2 = 0.03) and serum phosphate (P = 0.026; partial r2 = 0.04). Adjusting for vitamin D insufficiency or 25OHD levels did not affect the relationship between PTH and fat mass. For 25OHD, there were significant positive correlations with lumbar spine BMD and serum albumin, and significant negative correlations with PTH, total fat mass, trunk fat, and pelvic fat. On multivariate analysis, 25OHD was positively related to serum albumin (P = 0.008; partial r2 = 0.07) and negatively related to pelvic fat mass (P = 0.014; partial r2 = 0.05). Adjusting for PTH levels did not change the relationship between 25OHD and pelvic fat mass. We conclude that fat mass is a significant independent determinant of serum PTH levels, and that this relationship is independent of the inverse relationship between 25OHD and fat mass. This association between fat mass and PTH might contribute to the association between primary hyperparathyroidism and increased body weight.