Pharmacokinetics is the term used for how the body affects a drug once it is taken. Vitamin C, also known as ascorbic acid, is an essential water soluble vitamin. Meaning, the body does not make Vitamin C it must be taken in through the diet. In this study researchers will attempt to determine how the amount of water consumed affects the level of vitamin C in the blood (specifically the plasma component of the blood).

In this study researchers will take 13 subjects and place them on a Vitamin C restricted diet. Vitamin C levels will be measured twice a week on an outpatient basis until all subjects reach a desired low level of Vitamin C (12-15 micromolar plasma ascorbic acid concentration). Subjects will then be admitted and undergo 24 hour blood and urine collection. Following the collection of samples, subjects will then begin to receive Vitamin C orally (by mouth) and intravenously (injected into the vein). The dosage of Vitamin C will gradually increase from 30 mg-2500 mg divided into two daily doses. Blood and urine samples will be collected each time the dose is increased. The study will take approximately 18 weeks after which the subjects will be discharged in healthy condition....

Vitamin C is an essential water soluble vitamin. To date there have been no carefully controlled clinical trials to demonstrate how changes in vitamin C concentration in human plasma vary as a direct function of the amount ingested over a wide range. In this study, we plan to achieve a prescorbutic vitamin C plasma concentration of approximately 12-15 micromolar in thirteen healthy human volunteers and gradually replete these subjects with incremental doses of vitamin C to measure how their plasma concentrations will change as a function of the dose.

We will induce vitamin C deficiency in the outpatient setting by having volunteers adhere to a vitamin C restricted diet. As inpatients they will be placed on a more tightly restricted scorbutic diet. Plasma vitamin C will be monitored several times per week. When subjects have achieved a plasma AA concentration of 12-15 micromolar, blood sampling and urine collection over 24 hours will be performed. After platelets and leukocytes are collected, AA repletion will begin. Escalating doses of AA will be administered orally and intravenously for the remainder of their inpatient admission. Total daily doses of 30mg, 60mg, 100mg, 200mg, 400mg, 1000mg and 2500mg will be given in two divided doses. Bioavailability of AA will be determined at each dosage increment. When plasma AA concentration reaches steady state for each dose, subjects will undergo 36 hr plasma AA sampling and a timed 48 hr urine collection. At steady state of each of 4 to 5 doses, an apheresis procedure will be performed for collection of platelets and leukocytes. It is anticipated subjects will be discharged in healthy condition after 18 weeks.

• Hodges RE, Hood J, Canham JE, Sauberlich HE, Baker EM. Clinical manifestations of ascorbic acid deficiency in man. Am J Clin Nutr. 1971 Apr;24(4):432-43. No abstract available.
• Baker EM, Hodges RE, Hood J, Sauberlich HE, March SC, Canham JE. Metabolism of 14C- and 3H-labeled L-ascorbic acid in human scurvy. Am J Clin Nutr. 1971 Apr;24(4):444-54. No abstract available.
• Levine M. New concepts in the biology and biochemistry of ascorbic acid. N Engl J Med. 1986 Apr 3;314(14):892-902. Review. No abstract available.

• INCLUSION CRITERIA:

Males and females ages 18-35.

Normal volunteers selected from colleges/universities who will:

Spend within a fall or spring semester (approximately 12-14 weeks) as an inpatient resident on the endocrine-metabolic ward at NIH.

Be willing to adhere an AA restricted diet for 3 weeks prior to their NIH admission as well as for the duration of the time spent in the study as an inpatient at NIH.

Have veins adequate for venipuncture and be willing to undergo venipunctures approximately twice per week.

Refrain from ingestion of any medication and cigarette smoking.

Be able to give informed consent.

EXCLUSION CRITERIA:

Subject non-compliance with restricted diet.

Pregnancy as determined by history, physical exam and urine beta-HCG.

History of diabetes mellitus, bleeding disorders, kidney stones, glucose-6-phosphate dehydrogenase deficiency, family history of hemochromatosis/iron overload.

Platelet count less than 150,000/ul blood; prothrombin time/partial thromboplastin time (PT/PTT) greater than 1 second above normal upper limit.

Positive test for exposure to human immunodeficiency virus.

Positive tests for Hepatitis B surface antigen, core antibody or surface antibody.