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

This study is currently recruiting participants. (see Contacts and Locations)
Verified January 2015 by University of Tromso
Information provided by (Responsible Party):
University of Tromso Identifier:
First received: January 10, 2013
Last updated: January 5, 2015
Last verified: January 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

Further study details as provided by University of Tromso:

Primary Outcome Measures:
  • Free fraction of 25(OH)D [ Time Frame: 1 day ] [ Designated as safety issue: No ]

Secondary Outcome Measures:
  • DBP polymorphisms [ Time Frame: 1 day ] [ Designated as safety issue: No ]

Other Outcome Measures:
  • RNA expression in peripheral blood [ Time Frame: 1 day ] [ Designated as safety issue: No ]

Estimated Enrollment: 300
Study Start Date: February 2013
Estimated Study Completion Date: April 2016
Estimated 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
Genders Eligible for Study:   Both
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
Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below. For general information, see Learn About Clinical Studies.

Please refer to this study by its identifier: NCT01771380

Contact: Rolf Jorde, Professor 4777626827

University of Tromsø Recruiting
Tromsø, Norway, 9037
Contact: Elisabeth Dahlberg, PhD    4777644000   
Principal Investigator: rolf jorde, profesor         
Sponsors and Collaborators
University of Tromso
  More Information

No publications provided

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: January 5, 2015
Health Authority: Norway:National Committee for Medical and Health Research Ethics

Additional relevant MeSH terms:
Glucose Intolerance
Glucose Metabolism Disorders
Metabolic Diseases processed this record on March 30, 2015