Assessment of human vitamin C status

Since no reliable functional markers of human vitamin C status have been demonstrated, determination of vitamin C levels in blood plasma and/or leukocytes remains the current choice for individual and population assessments. Newer analytical techniques, especially high-performance liquid chromatography, allow determination of reduced (ascorbic acid), oxidized (dehydroascorbic acid), or total amounts of vitamin C in biological specimens or foods. Plasma levels of vitamin C forms are easily determined but may not reflect tissue content as well as leukocyte levels. The vitamin C content of leukocyte cell types varies severalfold and, unlike plasma, leukocytes may contain an appreciable fraction of dehydroascorbic acid. The effects of sex, age, cigarette smoking, drugs, and physiological factors on vitamin C levels are better known for plasma than leukocytes. To realize the potential of leukocytes as measures of vitamin C status, continued work is needed in standardizing the methodology and interpretive guidelines and simplifying the technique for blood processing. The search for specific functional markers of vitamin C deficiency should continue. Candidate markers may involve pathways of carnitine or collagen metabolism, immunocompetence, or antioxidant defense.