title: Is bone equally responsive to calcium and vitamin D intake from food vs. supplements? Use of (41)calcium tracer kinetic model.
abstract: BACKGROUND
  Few interventions directly compare equivalent calcium and vitamin D from dairy vs. supplements on the same bone outcomes. The radioisotope calcium-41 ((41)Ca) holds promise as a tracer method to directly measure changes in bone resorption with differing dietary interventions.
  
  
  OBJECTIVE
  Using (41)Ca tracer methodology, determine if 4 servings/day of dairy foods results in greater (41)Ca retention than an equivalent amount of calcium and vitamin D from supplements. Secondary objective was to evaluate the time course for the change in (41)Ca retention.
  
  
  METHODS
  In this crossover trial, postmenopausal women (n = 12) were dosed orally with 100 nCi of (41)Ca and after a 180 day equilibration period received dairy (4 servings/day of milk or yogurt; ~ 1300 mg calcium, 400 IU cholecalciferol (vitamin D3/day)) or supplement treatments (1200 mg calcium carbonate/day and 400 IU vitamin D3/day) in random order. Treatments lasted 6 weeks separated by a 6 week washout (WO). Calcium was extracted from weekly 24 h urine collections; accelerator mass spectrometry (AMS) was used to determine the (41/40)Ca ratio. Primary outcome was change in (41/40)Ca excretion. Secondary outcome was the time course for change in (41)Ca excretion during intervention and WO periods.
  
  
  RESULTS
  The (41/40)Ca ratio decreased significantly over time during both treatments; there was no difference between treatments. Both treatments demonstrated a significant retention of (41)Ca within 1-2 weeks (p = 0.0007 and p < 0.001 for dairy and supplements, respectively). WO demonstrated a significant decrease (p = 0.0024) in (41)Ca retention within 1-2 weeks, back to pre-intervention levels.
  
  
  CONCLUSIONS
  These data demonstrate that urinary (41)Ca retention is increased with an increase in calcium and vitamin D intake regardless of the source of calcium, and the increased retention occurs within 1-2 weeks.
authors.affiliation: Department of Nutrition, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States.
authors.forename: Tara S
authors.initials: TS
authors.lastname: Rogers
authors.affiliation: USDA, Agricultural Research Service, Western Human Nutrition Research Center, 430 West Health Sciences Drive, Davis, CA 95616, United States.
authors.forename: Marjorie G
authors.initials: MG
authors.lastname: Garrod
authors.affiliation: Department of Nutrition, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States.
authors.forename: Janet M
authors.initials: JM
authors.lastname: Peerson
authors.affiliation: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, United States.
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Hillegonds
authors.affiliation: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, United States.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Buchholz
authors.affiliation: Department of Nutrition, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States.
authors.forename: Elieke
authors.initials: E
authors.lastname: Demmer
authors.affiliation: Department of Nutrition, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States.
authors.forename: Christine
authors.initials: C
authors.lastname: Richardson
authors.affiliation: USDA, Agricultural Research Service, Western Human Nutrition Research Center, 430 West Health Sciences Drive, Davis, CA 95616, United States.
authors.forename: Erik R
authors.initials: ER
authors.lastname: Gertz
authors.affiliation: Department of Nutrition, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States; USDA, Agricultural Research Service, Western Human Nutrition Research Center, 430 West Health Sciences Drive, Davis, CA 95616, United States.
authors.forename: Marta D
authors.initials: MD
authors.lastname: Van Loan
keywords: 41Ca; 41Ca, calcium-41; AI, adequate intake; AMS, accelerator mass spectrometry; ANOVA, analysis of variance; BAP, bone specific alkaline phosphatase; BMC, bone mineral content; BMD, bone mineral density; BMI, body mass index; CTx, serum C terminal telopeptide of type 1 collagen; CV, coefficient of variation; Calcium supplement; DXA, dual energy X-ray absorptiometry; Dairy; ELISA, enzyme linked immune-sorbent assay; HCl, hydrochloric acid; Kinetic model; NDSR, Nutrition Data System for Research; NH4OH, ammonium hydroxide; PTH, parathyroid hormone; Postmenopausal; RCT, randomized controlled trial; RDA, recommended dietary allowances; WHNRC, Western Human Nutrition Research Center; nCi, nanocurrie; qCT, quantitative computed tomography