Objective: To investigate the relationship of parathyroid hormone (PTH) with dietary calcium and changes in body composition.
Design: Cross-sectional and 1-year longitudinal trial.
Subjects: Normal-weight young women (age: 18-31), 155 subjects analyzed at baseline, and data for 41 subjects analyzed prospectively between baseline and 12 months.
Measurements: Levels of fasting serum calcium and PTH, intakes of calcium (3-day diet records), and total body weight and body composition (dual energy X-ray absorptiometry).
Results: Baseline dietary calcium, regardless of whether unadjusted or adjusted for energy intake, did not predict baseline levels of fasting serum PTH. Change in dietary calcium also did not predict change in serum PTH. However, log PTH was significantly correlated with body fat mass (R = 0.27), but not lean mass at baseline (n = 155), independent of serum calcium (corrected R = 0.25). Further, 12-month changes (n = 41) in log PTH positively predicted the 12-month change in body weight (R = 0.32) and body fat (R = 0.32), but not lean mass even when controlled for age or change in serum calcium.
Conclusion: Fasting serum PTH was associated with increased fat mass, in both cross-sectional and prospective analysis. Thus, serum PTH may play a role in the regulation of body fat mass in young women.