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Assessment of the Free Fraction of 25-Hydroxyvitamin D in Serum and Its Regulation by Albumin and the Vitamin D-Binding Protein *
Abstract
We measured the free fraction of 25-hydroxyvitamin D (25OHD) in human serum and determined that 25OHD bound to a component with an affinity constant of 7 X 10(8) M-1 and a concentration of 4.5 X 10(-6) M. This concentration was equal to that of the vitamin D-binding protein (DBP) in the same serum sample. We removed DBP from the serum using actin affinity columns and found that the affinity for 25OHD of the remaining serum components was equivalent to that of human serum albumin (6 X 10(5) M-1). We then measured the free fractions of 25OHD, DBP, and albumin in normal and cirrhotic subjects. We calculated that 88 +/- 3% (+/- SD) and 83 +/- 8% of the 25OHD were bound to DBP in the serum of normal and cirrhotic subjects, respectively. We compared previously reported data for the free fraction and the free concentration of 1,25-dihydroxyvitamin D in these subjects with the current data for the free fraction and free concentration of 25OHD. The total concentrations and free fractions of both metabolites correlated to each other and to the DBP and albumin concentrations in these subjects, but the free concentrations of these metabolites did not. We conclude that 25OHD, like 1,25-dihydroxyvitamin D, is transported in blood bound primarily to DBP and albumin. Changes in the concentrations of DBP and albumin affected the total and free fractions of 25OHD in serum, but the actual free concentration of 25OHD was independent of such changes.
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Cited by
Vitamin D–Binding Protein and Vitamin D Status of Black Americans and White Americans
Powe, C. E., Evans, M. K., Wenger, J., Zonderman, A. B., Berg, A. H., Nalls, M., Tamez, H., Zhang, D., Bhan, I., Karumanchi, S. A., et al. (2013) · New England Journal of Medicine · doi:10.1056/nejmoa1306357 · Cited by 1,087
Consensus statement on vitamin D status assessment and supplementation: Whys, whens, and hows
Giustina, A., Bilezikian, J. P., Adler, R. A., Banfi, G., Bikle, D. D., Binkley, N. C., Bollerslev, J., Bouillon, R., Brandi, M. L., Casanueva, F. F., et al. (2024) · Endocrine Reviews · doi:10.1210/endrev/bnae009 · Cited by 392
Self-citationDzik, K. P., & Kaczor, J. J. (2019) · European Journal of Applied Physiology · doi:10.1007/s00421-019-04104-x · Cited by 357
Vitamin D Binding Protein: A Historic Overview
Bouillon, R., Schuit, F., Antonio, L., & Rastinejad, F. (2020) · Frontiers in Endocrinology · doi:10.3389/fendo.2019.00910 · Cited by 316
Vitamin D and the athlete: current perspectives and new challenges
Owens, D. J., Allison, R., & Close, G. L. (2018) · Sports Medicine · doi:10.1007/s40279-017-0841-9 · Cited by 223
Metadata
- Authors
- BIKLE, D. D., GEE, E., HALLORAN, B., KOWALSKI, M. A., RYZEN, E., & HADDAD, J. G.
- Venue
- The Journal of Clinical Endocrinology & Metabolism
- Publisher
- The Endocrine Society
- Published
- 1986-10
- Volume
- 63
- Issue
- 4
- Pages
- 954-959
- ISSN
- 0021-972X (ISSN-L)
- 1945-7197
- OpenAlex
- W2062361583
- Cited by
- 625
- References
- 0
- FWCI
- 3.64
- Type
- journal article
- Language
- en
- Open access
- closed
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- CoChat. (2026). Citation check: Assessment of the Free Fraction of 25-Hydroxyvitamin D in Serum and Its Regulation by Albumin and the Vitamin D-Binding Protein *. https://app.cochat.ai/papers/10.1210/jcem-63-4-954
- The paper
- BIKLE, D. D., GEE, E., HALLORAN, B., KOWALSKI, M. A., RYZEN, E., & HADDAD, J. G. (1986). Assessment of the Free Fraction of 25-Hydroxyvitamin D in Serum and Its Regulation by Albumin and the Vitamin D-Binding Protein *. The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jcem-63-4-954
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Contains information from the Semantic Scholar Academic Graph Datasets, made available under the ODC Attribution License (ODC-BY 1.0).
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