Am J Clin Nutr March 2014 vol. 99 no. 3 624-631
John F Aloia, Ruban Dhaliwal, Albert Shieh, Mageda Mikhail, Melissa Fazzari, Louis Ragolia, and Steven A Abrams
Winthrop University Hospital, Mineola, NY (JFA, RD, AS, MM, MF, and LR)
Baylor College of Medicine, Houston, TX (SAA).
Supported by Merck and Empire Clinical Research Investigator Program.
Address correspondence and reprint requests to JF Aloia, Winthrop University Hospital, 222 Station Plaza North, Suite 510, Mineola, NY 11501. E-mail: jaloia at winthrop.org.
Background: The maximal calcium absorption in response to vitamin D has been proposed as a biomarker for vitamin D sufficiency.
Objective: The objective was to determine whether there is a threshold beyond which increasing doses of vitamin D, or concentrations of serum 25-hydroxyvitamin D [25(OH)D], no longer increase calcium absorption.
Design: This was a placebo-controlled, dose-response, randomized, double-blind study of the effect of vitamin D on calcium absorption in healthy postmenopausal women. Seventy-six healthy postmenopausal women were randomly assigned to
- placebo or
- 800 IU (20 μg),
- 2000 IU (50 μg), or
- 4000 IU (100 μg) vitamin D3 for 8 wk.
The technique of dual isotopes of stable calcium was used with a calcium carrier to measure calcium absorption at baseline and after 8 wk.
Results: Seventy-one women with a mean ± SD age of 58.8 ± 4.9 y completed the study. The mean calcium intake was 1142 ± 509 mg/d and serum 25(OH)D was 63 ± 14 nmol/L at baseline. A statistically significant linear trend of an increase in calcium absorption adjusted for age and body mass index with increasing vitamin D3 dose or serum 25(OH)D concentration was observed. A 6.7% absolute increase in calcium absorption was found in the highest vitamin D3 group (100 μg).
No evidence of nonlinearity was observed in the dose-response curve.
Conclusions: No evidence of a threshold of calcium absorption was found with a serum 25(OH)D range from 40 to 130 nmol/L.
Calcium absorption in this range is not a useful biomarker to determine nutritional recommendations for vitamin D.
This trial was registered at clinicaltrials.gov as NCT01119378.
No threshold effect noticed
Is this linear with dose or with serum level?
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