Urinary Vitamin C Loss in Diabetic Subjects

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 vitamin C concentrations in patients with type 1 and type 2 diabetes and in matched healthy research subjects. Vitamin C concentrations in plasma, neutrophils (as a proxy for tissue concentrations) and in urine will be measured in outpatients. In those willing to be admitted to the Clinical Center, we will measure 24-hour urinary excretion of vitamin C while on a vitamin C free diet, and creatinine clearance, a measure of glomerular filtration rate. On day 2 of the inpatient study, subjects will receive a single 200mg dose of oral vitamin C and we will measure vitamin C concentrations in frequent blood and urine samples to determine the renal threshold and relative bioavailability for vitamin C. Single nucleotide polymorphisms (SNPs) will be determined in genomic DNA responsible for the two proteins mediating sodium-dependent vitamin C transport, SVCT1 and SVCT2. If low plasma and high urine vitamin C concentrations are found in diabetic subjects, further studies will be needed to explore mechanisms and to determine recommended dietary allowances for this patient population.

Study Overview

• Status: Recruiting
• Conditions: Diabetes

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 vitamin C concentrations in patients with type 1 and type 2 diabetes and in matched healthy research subjects. Vitamin C concentrations in plasma, neutrophils (as a proxy for tissue concentrations) and in urine will be measured in outpatients. In those willing to be admitted to the Clinical Center, we will measure 24-hour urinary excretion of vitamin C while on a vitamin C free diet, and creatinine clearance, a measure of glomerular filtration rate. On day 2 of the inpatient study, subjects will receive a single 200mg dose of oral vitamin C and we will measure vitamin C concentrations in frequent blood and urine samples to determine the renal threshold and relative bioavailability for vitamin C. Single nucleotide polymorphisms (SNPs) will be determined in genomic DNA responsible for the two proteins mediating sodium-dependent vitamin C transport, SVCT1 and SVCT2. If low plasma and high urine vitamin C concentrations are found in diabetic subjects, further studies will be needed to explore mechanisms and to determine recommended dietary allowances for this patient population.

• Study Type: Observational
• Enrollment (Estimated): 5000

Contacts and Locations

• Study Contact: Name: Irene T Rozga, R.N.; Phone Number: (301) 496-1069; Email: irene.rozga@nih.gov
• Study Contact Backup: Name: Ifechukwude C Ebenuwa, M.D.; Phone Number: (301) 435-6582; Email: ifechukwude.ebenuwa@nih.gov

Study Locations

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

Participation Criteria

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:

We propose to study of five thousand male and female subjects between the ages of 18 and 65. This will include healthy subjects and subjects with type 1 or type 2 diabetes. To be included in the study, study subjects should

• be in good general health
• have no significant illnesses that compromise clinical stability other than the complications of diabetes mellitus alone or in the context of metabolic syndrome. Subjects with ischemic heart disease and/or peripheral artery disease are eligible for arm 1 of the protocol.
• have serum creatinine < 2.5
• for healthy volunteers, be normotensive at the time of the study, with a blood pressure less than or equal to 140/90
• for diabetic subjects, blood pressure less than or equal to 170/95 as long as clinically stable and in usual state of health, for example, no chest pain, shortness of breath, headache, syncope or fatigue

The aim of this study is to determine whether diabetic subjects lose vitamin C in the urine in their normal clinical condition (i.e. while on treatment) and not in the native untreated state of uncontrolled hyperglycemia. Therefore the patients will not discontinue medication.

EXCLUSION CRITERIA (for arm 1):

Exclusion criteria will include the following:

• significant organ malfunction leading to clinical instability including liver disease, pulmonary disease, stroke and anemia at investigator discretion
• serious or chronic illness or history of serious or chronic illness resulting in clinical instability other than complications of diabetes
• pregnancy
• alcohol abuse, drug addiction or the use of illegal drugs
• positive HIV or hepatitis (B or C) screening tests (subjects will be notified of these test results).
• presence of other concomitant conditions which in the judgment of the investigators can influence vitamin C metabolism or vitamin C renal handling

EXCLUSION CRITERIA (for arms 2 and 3):

Exclusion criteria will include 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
• alcohol abuse, drug addiction or the use of illegal drugs
• positive HIV or hepatitis (B or C) screening tests (subjects will be notified of these test results).
• presence of other concomitant conditions which in the judgment of the investigators can influence vitamin C metabolism or vitamin C renal handling

For inpatient subjects, an additional exclusion criterion is consumption during the hospitalization of any foods or beverages other than those in the vitamin C free diet.

Study Plan

How is the study designed?

Design Details

• Observational Models: Cohort
• Time Perspectives: Prospective

Number of groups / cohorts

3

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	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	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	Calculate renal threshold of vitamin C in diabetic subjects as compared to healthy controls.	end of study

Collaborators and Investigators

• 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

General Publications

• Levine M. New concepts in the biology and biochemistry of ascorbic acid. N Engl J Med. 1986 Apr 3;314(14):892-902. doi: 10.1056/NEJM198604033141407. No abstract available.
• Goodwin JS, Goodwin JM, Garry PJ. Association between nutritional status and cognitive functioning in a healthy elderly population. JAMA. 1983 Jun 3;249(21):2917-21.
• Fata FT, Herzlich BC, Schiffman G, Ast AL. Impaired antibody responses to pneumococcal polysaccharide in elderly patients with low serum vitamin B12 levels. Ann Intern Med. 1996 Feb 1;124(3):299-304. doi: 10.7326/0003-4819-124-3-199602010-00003.

Helpful Links

• NIH Clinical Center Detailed Web Page

Study record dates

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): April 11, 2024
• Last Update Submitted That Met QC Criteria: April 10, 2024
• Last Verified: April 1, 2024

More Information

Terms related to this study

• Keywords: Diabetes Mellitus; Healthy Volunteer; Proteinuria; Renal Threshold; Plasma Concentrations
• Additional Relevant MeSH Terms: Glucose Metabolism Disorders; Metabolic Diseases; Endocrine System Diseases; Diabetes Mellitus
• 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