Urinary Vitamin C Loss in Diabetic Subjects

August 28, 2026 updated by: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Urinary Vitamin C Loss in Subjects With and Without Diabetes

Several studies have reported that diabetic subjects have lower plasma vitamin C concentrations than non-diabetic subjects. Although urinary vitamin C loss in diabetic subjects was reported to be increased in two studies, these are difficult to interpret due to lack of controlled vitamin C intake, inadequate sampling, lack of control subjects, or methodology uncertainties in vitamin C assay and sample processing. Consequently, it is unclear whether diabetic subjects truly have both low plasma and high urine vitamin C concentrations. We propose that low plasma vitamin C concentrations in diabetic subjects are due in part to inappropriate renal loss of vitamin C in these subjects but not in healthy controls. We will study nondiabetic controls and cohorts with diabetes. Vitamin C concentrations in plasma, RBCs, and urine will be measured in outpatients. In those willing to be admitted to the Clinical Center, we will measure vitamin C pharmacokinetics to determine the relative bioavailability for vitamin C in individuals with and without abnormal urinary loss of vitamin C (or renal leak). Single nucleotide polymorphisms (SNPs) will be determined in genomic DNA responsible for the two proteins mediating sodium dependent vitamin C transport, SVCT1 and SVCT2. We will also explore mechanisms underlying abnormal urinary vitamin C loss.

Study Overview

Status

Recruiting

Conditions

Detailed Description

Several studies have reported that diabetic subjects have lower plasma vitamin C concentrations than non-diabetic subjects. Although urinary vitamin C loss in diabetic subjects was reported to be increased in two studies, these are difficult to interpret due to lack of controlled vitamin C intake, inadequate sampling, lack of control subjects, or methodology uncertainties in vitamin C assay and sample processing. Consequently, it is unclear whether diabetic subjects truly have both low plasma and high urine vitamin C concentrations. We propose that low plasma vitamin C concentrations in diabetic subjects are due in part to inappropriate renal loss of vitamin C in these subjects but not in healthy controls. We will study nondiabetic controls and cohorts with diabetes. Vitamin C concentrations in plasma, RBCs, and urine will be measured in outpatients. In those willing to be admitted to the Clinical Center, we will measure vitamin C pharmacokinetics to determine the relative bioavailability for vitamin C in individuals with and without abnormal urinary loss of vitamin C (or renal leak). Single nucleotide polymorphisms (SNPs) will be determined in genomic DNA responsible for the two proteins mediating sodium dependent vitamin C transport, SVCT1 and SVCT2. We will also explore mechanisms underlying abnormal urinary vitamin C loss.

Study Type

Observational

Enrollment (Estimated)

5000

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • United States
    • Maryland
      • Bethesda, Maryland, United States, 20892
        • Recruiting
        • National Institutes of Health Clinical Center

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 65 years (Adult, Older Adult)

Accepts Healthy Volunteers

Yes

Sampling Method

Probability Sample

Study Population

Community sample.

Description

  • INCLUSION CRITERIA:

To be included in the study, study subjects should be:

  • Aged 18-65 years.

  • Either:

    • Have no diagnosis of diabetes: "nondiabetic controls", or
    • Have a diagnosis in their medical history of either Type 1 or Type 2 diabetes

EXCLUSION CRITERIA (for outpatient study, arm 1)

Exclusion criteria will include the following:

  • Unable or unwilling to provide a signed and dated informed consent form
  • Unable or unwilling to comply with study procedures and lifestyle considerations

EXCLUSION CRITERIA (for inpatient studies, arms 2 and 3)

Study participants interested in participating in Arms 2 and/or 3 will be excluded from this further participation if they meet any of the following:

  • significant organ malfunction leading to clinical instability including liver disease, pulmonary disease, ischemic heart disease, heart failure, stroke, peripheral vascular disease, and anemia at investigator discretion
  • other serious or chronic illness; history of serious or chronic illness; coronary artery disease, or peripheral vascular disease resulting in clinical instability
  • pregnancy or lactation
  • presence of other conditions which, in the judgment of the investigators, can influence vitamin C metabolism or vitamin C renal handling

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Observational Models: Cohort
  • Time Perspectives: Prospective

Cohorts and Interventions

Group / Cohort
Healthy Volunteers
Diabetes Type I
Subjects with Type I diabetes mellitus
Diabetes Type II
Subjects with Type II diabetes mellitus

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Plasma, neutrophil and RBC Vitamin C concentrates
Time Frame: end of study
Measurements of plasma, neutrophil and red blood cell vitamin c concentrations in diabetic subjects as compared to healthy controls.
end of study

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Urinary vitamin C concentration
Time Frame: end of study
Measurements of urinary vitamin c concentrations in diabetic subjects as compared to healthy controls.
end of study
Determine the renal threshold and relative bioavailability for vitamin C
Time Frame: end of study
Calculate renal threshold of vitamin C in diabetic subjects as compared to healthy controls.
end of study

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Investigators

  • Principal Investigator: Ifechukwude C Ebenuwa, M.D., National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

April 11, 2006

Study Registration Dates

First Submitted

October 27, 2003

First Submitted That Met QC Criteria

October 27, 2003

First Posted (Estimated)

October 28, 2003

Study Record Updates

Last Update Posted (Actual)

August 31, 2026

Last Update Submitted That Met QC Criteria

August 28, 2026

Last Verified

August 26, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 040021
  • 04-DK-0021

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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