title: Magnesium retention from metabolic-balance studies in female adolescents: impact of race, dietary salt, and calcium.
abstract: BACKGROUND
  Previously, we showed that black girls retained more calcium than white girls did and that salt loading negatively affected calcium retention. Racial differences likely exist in other bone minerals also, such as magnesium, in response to salt loading during growth.
  
  
  OBJECTIVE
  We studied racial differences in magnesium metabolism in response to dietary sodium and calcium during rapid bone growth.
  
  
  METHODS
  Twenty-seven white and 40 black girls (11-15 y old) were studied for 3 wk while they consumed low-sodium (1.3 g/d) and high-sodium (3.8 g/d) diets by using a randomized-order, crossover metabolic study with 3 dietary calcium intakes; the magnesium dietary intake was fixed at 230 mg/d. Urine and feces were collected during each 3-wk period in 24-h pools and analyzed for magnesium. A mixed-model ANOVA was used to determine the effect of race and dietary sodium with calcium intake as a covariate.
  
  
  RESULTS
  Salt loading or calcium intake had no significant effect on urinary magnesium excretion. Blacks excreted significantly less urinary magnesium (mean ± SD: 83.8 ± 25.6 mg/d) than did whites (94.9 ± 27.3 mg/d; P < 0.05). No effects were observed in fecal magnesium excretion. Magnesium retention was higher with the low-sodium diet (50.1 ± 44.0 mg/d) than with the high-sodium diet (39.3 ± 49.8 mg/d) (P < 0.05), with no effects of race or calcium intake. Salt loading had no effect on biomarkers. Whites had higher 25-hydroxyvitamin D and insulin-like growth factor binding protein 3 but lower 1,25-dihydroxyvitamin D and parathyroid hormone concentrations.
  
  
  CONCLUSIONS
  Blacks excreted less urinary magnesium than did whites. Magnesium retention was similar between races but higher with the low-sodium diet. Kinetic studies are needed to fully explain magnesium homeostasis. This trial was registered at clinicaltrials.gov as NCT01564238.
authors.affiliation: Nutrition Program, School of Public Health, University of Puerto Rico, San Juan, Puerto Rico. cristina.palacios@upr.edu
authors.forename: Cristina
authors.initials: C
authors.lastname: Palacios
authors.forename: Karin
authors.initials: K
authors.lastname: Wigertz
authors.forename: Michelle
authors.initials: M
authors.lastname: Braun
authors.forename: Berdine R
authors.initials: BR
authors.lastname: Martin
authors.forename: George P
authors.initials: GP
authors.lastname: McCabe
authors.forename: Linda
authors.initials: L
authors.lastname: McCabe
authors.forename: J Howard
authors.initials: JH
authors.lastname: Pratt
authors.forename: Munro
authors.initials: M
authors.lastname: Peacock
authors.forename: Connie M
authors.initials: CM
authors.lastname: Weaver
mesh_terms: D000293:Adolescent; D015415:Biomarkers; D044383:Black People; D015992:Body Mass Index; D001835:Body Weight; D002136:Calcium, Dietary / Q000008:administration & dosage*; D002648:Child; D018592:Cross-Over Studies; D004032:Diet; D005243:Feces / Q000737:chemistry; D005260:Female; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008274:Magnesium / Q000008:administration & dosage / Q000097:blood / Q000652:urine*; D009043:Motor Activity; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage*; D011795:Surveys and Questionnaires; D044465:White People
chemical_list: D015415:Biomarkers; D002136:Calcium, Dietary; D017673:Sodium Chloride, Dietary; D008274:Magnesium
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