title: Calcium retention in adolescent boys on a range of controlled calcium intakes.
abstract: BACKGROUND
  National calcium requirements in the United States for boys are based on data from girls. On average, boys develop larger skeletons than do girls, yet it is unknown whether the additional skeletal accretion in boys requires additional dietary calcium intake.
  
  
  OBJECTIVE
  The objective was to determine calcium retention in adolescent boys in response to a range of controlled intakes and to compare the intake needed for maximal retention in boys with that needed in adolescent girls studied under the same conditions.
  
  
  METHODS
  Thirty-one boys aged 12-15 y participated in 3-wk metabolic balance studies testing a range (700-2100 mg/d) of calcium intakes in a crossover study design with a 2-wk washout period. Calcium intake was varied by using a beverage fortified with calcium citrate malate. After a 1-wk equilibration period, calcium retention was calculated as dietary calcium intake minus the calcium excreted in the feces and urine over the following 2 wk. The dietary intake at which maximal calcium retention occurred was determined by using a nonlinear regression model. The results in boys were compared with those obtained in 35 adolescent girls previously studied under the same protocol.
  
  
  RESULTS
  Maximal calcium retention in boys was achieved at an intake of 1140 mg/d. Calcium retention was higher (by 171 +/- 38 mg/d) in boys than in girls at all calcium intakes studied.
  
  
  CONCLUSIONS
  The higher calcium retention in boys than in girls was attained through higher net calcium absorption and lower urinary excretion than in girls.
authors.affiliation: Purdue University, West Lafayette, IN, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Braun
authors.forename: Berdine R
authors.initials: BR
authors.lastname: Martin
authors.forename: Mark
authors.initials: M
authors.lastname: Kern
authors.forename: George P
authors.initials: GP
authors.lastname: McCabe
authors.forename: Munro
authors.initials: M
authors.lastname: Peacock
authors.forename: Zhen
authors.initials: Z
authors.lastname: Jiang
authors.forename: Connie M
authors.initials: CM
authors.lastname: Weaver
mesh_terms: D000293:Adolescent; D017195:Adolescent Nutritional Physiological Phenomena; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000378:metabolism / Q000493:pharmacokinetics* / Q000652:urine; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005243:Feces / Q000737:chemistry; D005260:Female; D005527:Food, Fortified; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D009751:Nutritional Requirements; D012727:Sex Characteristics; D016482:Urinalysis
chemical_list: D002136:Calcium, Dietary