title: Relative bioavailability of calcium-rich dietary sources in the elderly.
abstract: BACKGROUND
  The recent increase in the dietary calcium recommendation from 800 to 1200 mg/d for persons aged > 51 y has made it important to identify alternative high-calcium dietary sources that the elderly can use in meeting their calcium requirement.
  
  
  OBJECTIVE
  We determined the bioavailability of calcium from 3 different sources: orange juice fortified with calcium-citrate malate, skim milk, and a calcium carbonate supplement.
  
  
  METHODS
  Twelve subjects [9 women and 3 men with a mean (+/- SEM) age of 70 +/- 3 and 76 +/- 6 y, respectively] consumed low-calcium (300 mg/d) and high-calcium (1300 mg/d) diets for three 1-wk periods each during a 6-wk crossover study. The acute biochemical response to calcium from each of the 3 sources was assessed during a 4-h period after the initial breakfast meal of the high-calcium diet.
  
  
  RESULTS
  Postprandial suppression of serum parathyroid hormone did not differ significantly between the test meals containing calcium-fortified orange juice, the calcium carbonate supplement, and milk. This finding suggests that the calcium bioavailability from the 3 sources was equivalent. During the 1-wk high-calcium diet periods, fasting serum calcium increased by 3% (P < 0.0001), serum 1,25-dihydroxyvitamin D decreased by 20% (P < 0.0001), and a biomarker of bone resorption (serum N-telopeptide collagen cross-links) decreased by 14% (P < 0.02) compared with the low-calcium diet period. However, no differences among the supplemental calcium sources were found in these calcium-responsive measures or fasting serum parathyroid hormone concentration.
  
  
  CONCLUSIONS
  In elderly subjects, the calcium bioavailability of the 3 high-calcium dietary sources tested was equivalent, during both the acute postprandial and longer-term periods.
authors.affiliation: Mineral Bioavailability Laboratory, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston.
authors.forename: Ligia
authors.initials: L
authors.lastname: Martini
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Wood
mesh_terms: D000368:Aged; D000818:Animals; D001628:Beverages; D001682:Biological Availability; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000097:blood; D002119:Calcium Carbonate / Q000008:administration & dosage; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D002957:Citrus; D003094:Collagen / Q000097:blood; D024042:Collagen Type I; D018592:Cross-Over Studies; D019587:Dietary Supplements; D005215:Fasting; D005260:Female; D005502:Food; D005527:Food, Fortified; D006801:Humans; D008297:Male; D008892:Milk; D010281:Parathyroid Hormone / Q000097:blood; D010455:Peptides / Q000097:blood
chemical_list: D002136:Calcium, Dietary; D024042:Collagen Type I; D010281:Parathyroid Hormone; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D003094:Collagen; D002117:Calcitriol; D002119:Calcium Carbonate; D002118:Calcium