Association of intact parathyroid hormone levels with subsequent hip BMD loss: the Osteoporotic Fractures in Men (MrOS) Study.

INTRODUCTION: There is little information on the association between intact PTH (iPTH) and longitudinal changes in bone mineral density (BMD) in older men. This association was evaluated in relation to conditions related to higher iPTH [e.g. decreased renal function, low serum 25-hydroxyvitamin D (25[OH]D)].
METHODS: Eligible men were part of a random sample of 1593 community-dwelling individuals aged 65 yr or older participating in the Osteoporotic Fractures in Men study with baseline iPTH data. Of these, 1227 had at least two BMD measurements at the total hip and femoral neck over a mean follow-up of 4.5 yr. Annualized BMD change across iPTH quartiles was estimated using mixed-effects regression models, adjusting for age, serum calcium, serum 25(OH)D, estimated glomerular filtration rate, and other factors. Splines were used to identify more optimal iPTH thresholds associated with less BMD loss.
RESULTS: Among the cohort of 1138 eligible men, men in the highest quartile of iPTH (≥38 pg/ml) lost 0.46% per year at the total hip compared with men in the lowest iPTH quartile who lost 0.22% per year (P = 0.0004). Results were similar at the femoral neck. The association between iPTH and BMD loss was not modified by baseline estimated glomerular filtration rate or 25(OH)D status. Spline results suggested that iPTH levels below 30 pg/ml were more physiologically optimal than higher iPTH values in reducing BMD loss, although an exact threshold for optimal iPTH was not identified.
CONCLUSION: Older men with higher iPTH levels had approximately a 2-fold greater rate of BMD loss compared with men with lower iPTH levels, irrespective of estimated glomerular filtration rate and 25(OH)D.