25-Hydroxyvitamin D level does not reflect intestinal calcium absorption: an assay using strontium as a surrogate marker.
J Bone Miner Metab. 2014 May 24. [Epub ahead of print]
Camargo MB1, Vilaça T, Hayashi LF, Rocha OG, Lazaretti-Castro M.
1Division 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 at uol.com.br.
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.
PMID: 24858975
See also Vitamin D Life - controversy
- Vitamin D3 becomes Calcidiol which becomes Calcitriol
- Calcium bioavailability and how much to take
- More Calcium absorbed with more vitamin D – 6.7% more with 4000 IU – RCT March 2014
- Calcium in blood (tightly regulated) did not increase when increase vitamin D to 40 ng – RCT Oct 2013
- Little change in Calcium absorption when taking 400 vs 4,000 IU of vitamin D – Oct 2012
- Calcium absorption increased 18 pct with high level of vitamin D – June 2012
- Controversy: Too much Calcium if increase Vitamin D
some say major problem with just 2,000 IU of vitamin D, others say no problem with 10,000 IU