title: 25-Hydroxyvitamin D level does not reflect intestinal calcium absorption: an assay using strontium as a surrogate marker.
abstract: There is conflicting evidence as to the optimal serum 25-hydroxyvitamin D [25(OH)D] concentration for intestinal calcium absorption (Abs-Ca). Our purpose was to assess the relationship between vitamin D status and Abs-Ca in postmenopausal women. Fifty volunteers with low bone mass were grouped according to their serum 25(OH)D concentration as follows: mild deficient, <50 nmol/L (DEF) and sufficient, ≥75 nmol/L (SUF). The subjects were submitted to an oral strontium overload test to assess their Abs-Ca. Fasting blood samples were obtained to perform the relevant hormonal and biochemical tests. After the subjects received the test solution, blood samples were drawn at 30, 60, 120, and 240 min to determine the strontium concentrations. Abs-Ca was indirectly expressed as the area under the serum strontium concentration curve (AUC). A repeated measures ANOVA was performed to determine the differences among the groups. Pearson's correlation and multiple linear regression analysis were used to study the associations between the variables. The mean 25(OH)D and 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations differed between the groups (SUF vs. DEF) as follows: 98.7 ± 18.2 vs. 38.4 ± 8.5 nmol/L (p < 0.001) and 36.2 ± 10.2 vs. 24.9 ± 4.6 pg/mL (p < 0.001), respectively. There was no statistically significant difference between the groups for parathyroid hormone and AUC. Only 1,25(OH)2D influenced the strontium absorption in the last 2 h of the test. In the studied population, no correlation between levels of 25(OH)D and Abs-Ca was found. Only 1,25(OH)2D influenced Abs-Ca as measured by a strontium absorption test.
authors.affiliation: Division of Endocrinology, School of Medicine, Federal University of São Paulo/UNIFESP, Avenida Nove de Julho, 5581, Apto. 30, Jardim Paulista, São Paulo, SP, CEP 01407-200, Brazil, lilacamargo@uol.com.br.
authors.forename: Marília Brasilio Rodrigues
authors.initials: MB
authors.lastname: Camargo
authors.forename: Tatiane
authors.initials: T
authors.lastname: Vilaça
authors.forename: Lilian Fukusima
authors.initials: LF
authors.lastname: Hayashi
authors.forename: Olguita G Ferreira
authors.initials: OG
authors.lastname: Rocha
authors.forename: Marise
authors.initials: M
authors.lastname: Lazaretti-Castro
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry; D002118:Calcium / Q000378:metabolism*; D002136:Calcium, Dietary / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D008875:Middle Aged; D012867:Skin / Q000378:metabolism; D013324:Strontium / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism
chemical_list: D002136:Calcium, Dietary; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002118:Calcium; D013324:Strontium