We're building a better ClinicalTrials.gov. Check it out and tell us what you think!
Working…
ClinicalTrials.gov
ClinicalTrials.gov Menu

Study of the Effects of Vitamin C on Patients With Type 2 Diabetes

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details.
 
ClinicalTrials.gov Identifier: NCT00001870
Recruitment Status : Completed
First Posted : November 4, 1999
Last Update Posted : March 4, 2008
Sponsor:
Information provided by:
National Institutes of Health Clinical Center (CC)

Study Description
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information
Brief Summary:

Diabetes is a disease characterized by decreased sensitivity to the action on insulin to promote sugar (glucose) use and blood vessel relaxation (vasodilation) in muscle. Insulin's ability to cause blood vessel relaxation is controlled, in part, by nitric oxide (NO).

Nitric oxide is a substance produced by the cells lining blood vessel walls (endothelium). Increased blood flow to the muscle accounts for increased sugar (glucose) to areas of the body. Therefore, if the cells of blood vessel walls (endothelium) are not functioning properly it may contribute to insulin resistance.

Injections of Vitamin C directly into the arteries have been shown to improve blood vessel reaction to nitric oxide in diabetic patients. Researchers believe this may be due to Vitamin C's ability to increase the levels of nitric oxide in blood vessels.

The goal of this study is to determine the effects of vitamin C on both insulin sensitivity and endothelium function of patients with type 2 diabetes. An additional goal of the study is to determine the effects of vitamin C on patients with vitamin C deficiency.

Patients participating in this study will undergo a series of testes to determine insulin sensitivity and blood vessel reactivity. Patients will be divided into two groups. One group will receive doses of oral vitamin C. The other group will receive doses of a placebo (inactive pill not containing vitamin C). Patients will receive the medications for four weeks and then be tested again for insulin sensitivity and blood vessel reactivity.

Researchers believe that doses of vitamin C in diabetics or patients with vitamin C deficiency will improve insulin sensitivity and function of endothelium. Results gathered form this study may provide information about vitamin C levels in diabetics and may lead to the development of new therapies to treat insulin resistance and endothelium dysfunction.


Condition or disease Intervention/treatment Phase
Diabetes Mellitus, Non-Insulin Dependent Non-Insulin Dependent Drug: Acetylcholine Phase 2

Detailed Description:
Diabetes is characterized by decreased sensitivity to the actions of insulin to promote both glucose utilization and vasodilation in skeletal muscle beds. Insulin's vasodilator action is mediated, in part, by endothelial-derived nitric oxide (NO). Increased blood flow accounts for approximately 25% of the increase in skeletal muscle glucose disposal mediated by insulin. Therefore, endothelial dysfunction may contribute to insulin resistance. Intraarterial administration of vitamin C improves NO-dependent vascular reactivity in diabetic subjects (but not normal subjects). This may be due to antioxidant properties of vitamin C that result in relative increases in the level of NO in the diabetic vasculature. In this exploratory protocol, our primary objective is to assess the effects of oral administration of vitamin C on both insulin sensitivity and endothelial function in subjects with type 2 diabetes. A secondary, peripheral objective, is to study these effects in vitamin C-deficient clinical research volunteers. Hyperinsulinemic euglycemic glucose clamp procedures and forearm blood flow measurements will be used to assess both insulin sensitivity and vascular reactivity in diabetic subjects and clinical research volunteers who have plasma vitamin C levels less than 30 microM. The subjects will then be given either placebo or oral vitamin C supplementation (800 mg/day) for four weeks and assessment of insulin sensitivity and vascular reactivity will be repeated. Plasma levels of vitamin C will be measured to confirm that subjects in the experimental group have an appropriate increase in vitamin C levels. We hypothesize that chronic oral administration of vitamin C to diabetic or clinical research volunteers who are deficient in vitamin C will improve insulin sensitivity and endothelial function. Our study will provide information about vitamin C levels in diabetic subjects and may suggest a potential therapy to significantly improve endothelial dysfunction and insulin resistance.
Study Design
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information

Layout table for study information
Study Type : Interventional  (Clinical Trial)
Enrollment : 150 participants
Primary Purpose: Treatment
Official Title: An Exploratory Study of the Effects of Oral Vitamin C Administration on Insulin Sensitivity and Vascular Reactivity in Subjects With Type 2 Diabetes
Study Start Date : January 1999
Study Completion Date : December 2004

Resource links provided by the National Library of Medicine

MedlinePlus related topics: Vitamin C

Arms and Interventions
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information


Outcome Measures
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information

Eligibility Criteria
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information

Information from the National Library of Medicine

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, Learn About Clinical Studies.


Layout table for eligibility information
Ages Eligible for Study:   Child, Adult, Older Adult
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes
Criteria

INCLUSION CRITERIA:

DIABETIC SUBJECTS:

Males and non-pregnant females between the ages of 18 and 65 in good general health except for type 2 diabetes controlled with diet and/or oral hypoglycemic agents.

Patients found to have plasma vitamin C levels less than 40 microliter M, will be enrolled into the protocol and taken off hypoglycemic agents approximately one week prior to each study.

VITAMIN C-DEFICIENT CLINICAL RESEARCH VOLUNTEERS:

Adults between the ages of 18 and 35 in good general health and on no drugs or medications.

EXCLUSION CRITERIA:

ALL SUBJECTS:

Pregnancy, liver disease, pulmonary disease, renal insufficiency, coronary heart disease, heart failure, peripheral vascular disease, coagulopathy, disease predisposing to vasculitis or Raynaud's phenomenon, bleeding disorders, kidney stones, glucose-6-phosphate dehydrogenase deficiency, family history of hemochromatosis/iron overload, platelet count less than 150,000/ml blood, prothrombin time/partial thromboplastin time (PT/PTT) greater than 1 second above the normal range, inability to give informed consent for all procedures, and positive tests for HIV, or hepatitis B or C.

DIABETIC SUBJECTS:

In addition, to the above exclusion criteria, the presence of proteinuria greater than 500 mg/24 hrs, proliferative retinipathy, or diabetic neuropathy

VITAMIN C-DEFICIENT CLINICAL RESEARCH VOLUNTEERS:

All the above exclusion criteria.

Contacts and Locations
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its ClinicalTrials.gov identifier (NCT number): NCT00001870


Locations
Layout table for location information
United States, Maryland
National Center for Complementary and Alternative Medicine (NCCAM)
Bethesda, Maryland, United States, 20892
Sponsors and Collaborators
National Center for Complementary and Integrative Health (NCCIH)
More Information
Go to 
Top of Page Study Description Study Design Arms and Interventions Outcome Measures Eligibility Criteria Contacts and Locations More Information
Publications:

Layout table for additonal information
ClinicalTrials.gov Identifier: NCT00001870    
Other Study ID Numbers: 990033
99-AT-0033
First Posted: November 4, 1999    Key Record Dates
Last Update Posted: March 4, 2008
Last Verified: December 2004
Keywords provided by National Institutes of Health Clinical Center (CC):
Insulin Resistance
Oxidative Stress
Antioxidant
Endothelial Function
 Glucose Clamp
Type 2 Diabetes
Vitamin C Deficiency
Additional relevant MeSH terms:
Layout table for MeSH terms
Diabetes Mellitus
Diabetes Mellitus, Type 2
Glucose Metabolism Disorders
Metabolic Diseases
Endocrine System Diseases
Acetylcholine
 Vasodilator Agents
Cholinergic Agonists
Cholinergic Agents
Neurotransmitter Agents
Molecular Mechanisms of Pharmacological Action
Physiological Effects of Drugs