Protocol Number: 99-AT-0033

Title:

An Exploratory Study of the Effects of Oral Vitamin C Administration on Insulin Sensitivity and Vascular Reactivity in Subjects with Type 2 Diabetes

Number:

99-AT-0033

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.

Sponsoring Institute:

National Center for Complementary and Alternative Medicine (NCCAM)

Recruitment Detail

Type: Active Accrual Of New Subjects

Gender: Male & Female

Referral Letter Required: No

Population Exclusion(s): Children

Eligibility 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.

Special Instructions: Currently Not Provided

Keywords:

Insulin Resistance

Oxidative Stress

Antioxidant

Endothelial Function

Glucose Clamp

Recruitment Keywords:

Type 2 Diabetes

Vitamin C Deficiency

Conditions:

Diabetes Mellitus, Non-Insulin Dependent

Non-Insulin Dependent

Investigational Drug(s):

Acetylcholine

Investigational Device(s):

None

Contacts:

Patient Recruitment and Public Liaison Office
Building 61
10 Cloister Court
Bethesda, Maryland 20892-4754
Toll Free: 1-800-411-1222
TTY: 301-594-9774 (local),1-866-411-1010 (toll free)
Fax: 301-480-9793

Electronic Mail:prpl@mail.cc.nih.gov

Citations:

Role of glucose and insulin resistance in development of type 2 diabetes mellitus: results of a 25-year follow-up study

Lilly lecture 1987 The triumvirate: beta-cell, muscle, liver A collusion responsible for NIDDM

Impaired glucose tolerance as a disorder of insulin action Longitudinal and cross-sectional studies in Pima Indians

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