title: PTH and 1.25 vitamin D response to a low-calcium diet is associated with bone mineral density in renal stone formers.
abstract: BACKGROUND
  Renal calcium stones and hypercalciuria are associated with a reduced bone mineral density (BMD). Therefore, the effect of changes in calcium homeostasis is of interest for both stones and bones. We hypothesized that the response of calciuria, parathyroid hormone (PTH) and 1.25 vitamin D to changes in dietary calcium might be related to BMD.
  
  
  METHODS
  A single-centre prospective interventional study of 94 hyper- and non-hypercalciuric calcium stone formers consecutively retrieved from our stone clinic. The patients were investigated on a free-choice diet, a low-calcium diet, while fasting and after an oral calcium load. Patient groups were defined according to lumbar BMD (z-score) obtained by dual X-ray absorptiometry (group 1: z-score <-0.5, n = 30; group 2: z-score -0.5-0.5, n = 36; group 3: z-score >0.5, n = 28). The effect of the dietary interventions on calciuria, 1.25 vitamin D and PTH in relation to BMD was measured.
  
  
  RESULTS
  An inverse relationship between BMD and calciuria was observed on all four calcium intakes (P = 0.009). On a free-choice diet, 1.25 vitamin D and PTH levels were identical in the three patient groups. However, the relative responses of 1.25 vitamin D and PTH to the low-calcium diet were opposite in the three groups with the highest increase of 1.25 vitamin D in group 1 and the lowest in group 3, whereas PTH increase was most pronounced in group 3 and least in group 1.
  
  
  CONCLUSIONS
  Calcium stone formers with a low lumbar BMD exhibit a blunted response of PTH release and an apparently overshooting production of 1.25 vitamin D following a low-calcium diet.
authors.affiliation: Department of Nephrology and Hypertension, Inselspital, University of Bern, Freiburgstrasse 10, CH-3010 Bern, Switzerland. andreas.pasch@insel.ch
authors.forename: Andreas
authors.initials: A
authors.lastname: Pasch
authors.forename: Felix J
authors.initials: FJ
authors.lastname: Frey
authors.forename: Ute
authors.initials: U
authors.lastname: Eisenberger
authors.forename: Markus G
authors.initials: MG
authors.lastname: Mohaupt
authors.forename: Olivier
authors.initials: O
authors.lastname: Bonny
mesh_terms: D000328:Adult; D015519:Bone Density / Q000502:physiology*; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood / Q000652:urine; D002136:Calcium, Dietary / Q000008:administration & dosage*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D053565:Hypercalciuria / Q000150:complications / Q000378:metabolism; D007669:Kidney Calculi / Q000150:complications / Q000378:metabolism; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D011446:Prospective Studies
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D002117:Calcitriol; D002118:Calcium