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PTH does not plateau with increasing vitamin D, but does decrease with patient age – Aug 2012

Effects of Age and Serum 25-OH-Vitamin D on Serum Parathyroid Hormone Levels

The Journal of Clinical Endocrinology & Metabolism August 29, 2012 jc.2012-2276
A. Valcour, F. Blocki, D. M. Hawkins and Sudhaker D. Rao
Center for Esoteric Testing (A.V.), Lab Corp., Burlington, North Carolina 27216; DiaSorin (F.B.), Stillwater, Minnesota 55082; School of Statistics (D.M.H.), University of Minnesota, Minneapolis, Minnesota 55455; and Bone and Mineral Research Laboratory (S.D.R.), Henry Ford Hospital, Detroit, Michigan 48202
Address all correspondence and requests for reprints to: Frank Blocki, Diasorin, 1951 Northwestern Avenue, Stillwater, Minnesota 55082. E-mail: frank.blocki at diasorin.com.

Context: Several studies define optimal serum 25-hydroxyvitamin D (25-OHD) levels based on serum PTH level reaching an asymptote. However, results differ widely, ranging from 25-OHD levels of 12–44 ng/ml: many studies are constrained by small sample size.

Objective: The objective of the study was to determine the relationship between serum PTH and 25-OHD levels and age in a very large reference laboratory database.

Design: This was a detailed cross-sectional analysis of 312,962 paired serum PTH and 25-OHD levels measured from July 2010 to June 2011.

Results: Median PTH levels and the proportion of patients (PTH > 65 pg/ml), from 63 successive 25-OHD frequency classes of 5000 patients, provide smooth, exceptionally well-fitted curves (R2 = 0.994 and R2 = 0.995, respectively) without discernible inflection points or asymptotes but with striking age dependencies.
Serum 25-OHD was below the recent Institute of Medicine sufficiency guidance of 20 ng/ml in 27% (85,000) of the subjects.
More importantly, 40 and 51% of subjects (serum 25-OHD <20 and 10 ng/ml, respectively) had biochemical hyperparathyroidism (PTH > 65 pg/ml).

Conclusions: This analysis, despite inevitable inherent limitations, introduces several clinical implications.

  1. First, median 25-OHD-dependent PTH levels revealed no threshold above which increasing 25-OHD fails to further suppress PTH.
  2. Second, the large number of subjects with 25-OHD deficiency and hyperparathyroidism
    reinforces the Third International Workshop on Asymptomatic Primary Hyper parathyroidism’s recommendations to test for, and replete, vitamin D depletion before considering parathyroidectomy.
  3. Third, strong age dependency of the PTH-25-OHD relationship likely reflects the composite effects of age-related decline in calcium absorption and renal function.
  4. Finally, this unselected large population database study could guide clinical management of patients based on an age-dependent, PTH-25-OHD continuum.

Note: Diasorin makes a vitamin D blood tester
Note: Most other studies have found a threshold for PTH, that is, it does NOT keep decreasing with increasing vitamin D levels

See also VitaminDWiki