title: Isotope concentrations from 24-h urine and 3-h serum samples can be used to measure intestinal magnesium absorption in postmenopausal women.
abstract: Studies suggest a link between magnesium status and osteoporosis. One barrier to more conclusive research on the potential relation is measuring intestinal magnesium absorption (MgA), which requires the use of stable isotopes and a ≥6-d stool or 3-d urine collection. We evaluated alternative methods of measuring MgA. We administered 2 stable magnesium isotopes to 15 postmenopausal women (cohort 1) aged 62 ± 8 y with a dietary magnesium intake of 345 ± 72 mg/d. Participants fasted from 1200 h to 0700 h and then consumed breakfast with ∼23 mg of oral ²⁶Mg and ∼11 mg of i.v. ²⁵Mg. We measured magnesium isotope concentrations in 72-h urine, spot urine (36, 48, 60, and 72 h), and spot serum (1, 3, and 5 h) samples collected after isotope dosing. We calculated MgA using the dose-corrected fraction of isotope concentrations from the 72-h urine collection. We validated new methods in 10 postmenopausal women (cohort 2) aged 59 ± 5 y with a dietary magnesium intake of 325 ± 122 mg/d. In cohort 1, MgA based on the 72-h urine collection was 0.28 ± 0.08. The 72-h MgA correlated most highly with 0-24 h urine MgA value alone (ρ = 0.95, P < 0.001) or the mean of the 0-24 h urine and the 3-h (ρ = 0.93, P < 0.001) or 5-h (ρ = 0.96, P < 0.001) serum MgA values. In cohort 2, Bland-Altman bias was lowest (-0.003, P = 0.82) using means of the 0-24 h urine and 3-h serum MgA values. We conclude that means of 0-24 h urine and 3-h serum MgA provide a reasonable estimate of 72-h MgA. However, if researchers seek to identify small changes in MgA, we recommend a 3-d urine or extended stool collection.
authors: Department of Medicine, School of Medicine and Public Health.
authors: Karen E
authors: KE
authors: Hansen
authors: Andrea C
authors: AC
authors: Nabak
authors: Rachael Erin
authors: RE
authors: Johnson
authors: Sheeva
authors: S
authors: Marvdashti
authors: Nicholas S
authors: NS
authors: Keuler
authors: Martin M
authors: MM
authors: Shafer
authors: Steven A
authors: SA
authors: Abrams
mesh_terms: D000284:Administration, Oral; D000368:Aged; D062408:Breakfast; D015331:Cohort Studies; D004032:Diet; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000502:physiology / Q000503:physiopathology*; D007554:Isotopes; D008274:Magnesium / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism* / Q000652:urine; D008277:Magnesium Oxide / Q000008:administration & dosage; D008286:Malabsorption Syndromes / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology / Q000652:urine; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D017698:Postmenopause; D019518:Postprandial Period; D011237:Predictive Value of Tests; D013054:Spectrophotometry, Atomic
chemical_list: D007554:Isotopes; D008277:Magnesium Oxide; D008274:Magnesium