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Measurement of the Free Fraction of 25-hydroxyvitamin D in Serum

This study has been completed.
Information provided by (Responsible Party):
University of Tromso Identifier:
First received: January 10, 2013
Last updated: September 18, 2015
Last verified: September 2015
In the circulation 25-hydroxyvitaminD (25(OH)D) is bound to the vitamin D binding protein (DBP) and albumin. According to the free hormone hypothesis, it is, however, the free fraction that is biologically active. Polymorphisms in DBP are related to the serum level of 25(OH)D. As these polymorphisms may also affect the binding affinities for 25(OH)D, the total serum 25(OH)D may not necessary reflect the free fraction. To test this hypothesis, we will calculate the free fraction of 25(OH)D by correction for DBP and albumin content, and also measure free 25(OH)D from equilibrium dialysis and ultra filtration. Furthermore, we will relate total serum 25(OH)D as well as the free and biologically active (free- albumin-bound) 25(OH)D to the well established vitamin D effect marker serum parathyroid hormone as well as to the RNA expression in peripheral blood to evaluate the biological importance of the free versus the total fraction of 25(OH)D. We will invite 300 subjects from an ongoing vitamin D supplementation study to participate in the study which will be one visit only and include collection of blood samples.

Impaired Glucose Tolerance

Study Type: Observational
Study Design: Observational Model: Cohort
Time Perspective: Cross-Sectional
Official Title: Measurement of the Free Fraction of 25-hydroxyvitamin D in Serum

Resource links provided by NLM:

Further study details as provided by University of Tromso:

Primary Outcome Measures:
  • Free fraction of 25(OH)D [ Time Frame: 1 day ]

Secondary Outcome Measures:
  • DBP polymorphisms [ Time Frame: 1 day ]

Other Outcome Measures:
  • RNA expression in peripheral blood [ Time Frame: 1 day ]

Enrollment: 78
Study Start Date: February 2013
Study Completion Date: August 2015
Primary Completion Date: June 2015 (Final data collection date for primary outcome measure)
Subjects with impaired glucose tolerance


Ages Eligible for Study:   25 Years to 85 Years   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes
Sampling Method:   Non-Probability Sample
Study Population
Subjects with known impaired glucose tolerance

Inclusion Criteria:

  • Impaired glucose tolerance
  • living in the Tromsø area

Exclusion Criteria

  • pregnancy
  • serious illness
  Contacts and Locations
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Please refer to this study by its identifier: NCT01771380

University of Tromsø
Tromsø, Norway, 9037
Sponsors and Collaborators
University of Tromso
  More Information

Responsible Party: University of Tromso Identifier: NCT01771380     History of Changes
Other Study ID Numbers: Tromsø-Endo-2013-1
Study First Received: January 10, 2013
Last Updated: September 18, 2015

Additional relevant MeSH terms:
Glucose Intolerance
Glucose Metabolism Disorders
Metabolic Diseases
Vitamin D
Growth Substances
Physiological Effects of Drugs
Bone Density Conservation Agents processed this record on August 21, 2017