Age-related decline in serum parathyroid hormone in maintenance hemodialysis patients is independent of inflammation and dietary nutrient intake
Abstract
Background
There is a direct relationship between age and serum parathyroid hormone (iPTH) in the normal population, but several studies suggest this relationship is reversed in maintenance hemodialysis (MHD) patients. The pathophysiologic basis of this age-related decline in serum iPTH levels remains unclear, although others have proposed that it is related to low dietary phosphorus intakes.
Methods
We conducted a prospective, cross-sectional evaluation of the relationship between age and serum iPTH levels and factors affecting this relationship. All participating subjects were asked to complete a 3-day food diary. The charts were reviewed to obtain routinely measured laboratory values over the preceding 3 months, and serum was collected to measure markers of systemic inflammation.
Results
Ninety-two MHD patients (47 men; age, 51.3±14.9 [standard deviation] years; median dialysis vintage, 25.8 months) were studied. Age was inversely correlated with both serum phosphorus and iPTH; these relationships remained significant even when the data were adjusted for diabetic status, dialysis vintage, and dietary nutrient intake. However, there were no associations of age, serum phosphorus, or iPTH with dietary intakes of protein, calories, phosphorus, or calcium either on univariate or multivariate analyses. Markers of systemic inflammation (serum C-reactive protein, and alpha1 acid glycoprotein) did not correlate with age, serum phosphorus, and iPTH or dietary nutrient intake. On the other hand, serum albumin, which may reflect long-term effects of inflammation, did correlate inversely with age and positively with serum phosphorus.
Conclusions
Our cross-sectional study confirms that there are age-related lower levels of both serum phosphorus and iPTH in MHD patients. The mechanisms regarding the inverse relationship between serum phosphorus and age are unclear, but may not be caused by low phosphorus intake or systemic inflammation. In elderly MHD patients, the reduced responsiveness of parathyroid glands may be related to age-dependent accumulation of uremic toxins.
∗Division of Nephrology and Hypertension, Harbor-UCLA Medical Center, Torrance, CA, USA
†Department of Pediatrics, Harbor-UCLA Medical Center, Torrance, CA, USA
‡Research and Education Institute, Harbor-UCLA Medical Center, Torrance, CA, USA
§David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
∥UCLA School of Public Health, Los Angeles, CA, USA
¶Division of Nephrology, University of California, Davis, Davis, CA, USA
Address reprint requests to Rajnish Mehrotra, MD, Division of Nephrology and Hypertension, Harbor-UCLA Medical Center, 1124 W. Carson St, Torrance, CA 90502 USA
1 Rajnish Mehrotra and Oupatham Supasyndh contributed equally to this work.
ABSTRACT