Vitamin leukocyte concentration

About 70% of blood ascorbate is in plasma and erythrocytes (which do not concentrate the vitamin from plasma). The remainder is in white cells, which have a marked ability to concentrate ascorbate mononuclear leukocytes achieve 80-fold, platelets 40-fold, and granulocytes 25-fold concentration, compared with plasma concentration. In adequately nourished subjects, and those receiving supplements, the ascorbate concentration in erythrocytes, platelets, and granulocytes, but not in mononuclear leukocytes, is correlated with plasma concentration. Mononuclear leukocytes concentrate ascorbate independendy of plasma concentration (Evans et al., 1982). In deficiency, as plasma concentrations of ascorbate fall, mononuclear leukocyte, granulocyte, and platelet concentrations of ascorbate are protected to a considerable extent. As discussed in Section 13.5.2, the leukocyte content of ascorbate is used as an index ofvitamin C nutritional status, but in view of the differing capacity of different cell types to accumulate the vitamin, differential white cell counts are essential to interpret the results. 

Vitamin C status is generally assessed by estimating the saturation of body reserves or measuring plasma and leukocyte concentrations of the vitamin. Urinary excretion of hydroxyproline-containing peptides is reduced in people with inadequate vitamin C status, but a number of other factors that affect bone and connective tissue turnover confound interpretation of the results (Bates, 1977). The ratio of deoxypyridinolineipyridinoline compounds derived from collagen cross-links provides a more useful index, but is potentially affected by copper status (Tsuchiya and Bates, 1997). 

The Effect of Smoking on Vitamin C Requirements There is evidence that smokers have a higher requirement for vitamin C than nonsmokers. A number of studies have shown lower plasma and leukocyte concentrations of vitamin C in smokers, but many also report lower intake of the vitamin by smokers. The rate of catabolism of ascorbate is up to 40% greater in smokers than nonsmokers (Kallner et al., 1981), and therefore their vitamin C requirement may be almost twice that of nonsmokers. 

Vitamin C levels can be determined in stored blood or blood components such as serum, plasma, or leukocytes if particular preservation steps are performed during preparation. The concentration of vitamin C is stable in whole blood for several hours with negligible decay. If whole blood is centrifuged and serum or plasma obtained, vitamin C starts to disappear immediately. Therefore, the stabilization of vitamin C by metaphosphoric acid or other substances is required if such aliquots are to be used to determine vitamin C concentration in future analyses. The need for preserving aliquots is unnecessary in the determination of other antioxidant substances such as vitamin E or carotenoids. The preservation issue may also be a reason that blood determinations of antioxidants, such as (3-carotene or vitamin E, and their relation to disease risk are found more frequently than vitamin C (Comstock a/., 1992). 

Richards, J. B., Valdes, A. M., Gardner, J. P. et al. 2007. Higher serum vitamin D concentrations are associated with longer leukocyte telomere length in women. Am J Clin Nutr 86 1420-5. 

A problem arises in the interpretation of leukocyte ascorbate concentrations because of the different capacity of different classes of leukocytes to accumulate the vitamin. Granulocytes are saturated at a concentration of about 530 pmol/10 cells, while mononuclear leukocytes can accumulate 2.5 times more ascorbate. A considerable mythology has developed to the effect that vitamin C requirements are increased in response to infection, inflammation, and trauma, based on reduced leukocyte concentrations of ascorbate in these conditions. However, the fall in leukocyte ascorbate can be accounted for by an increase in the proportion of granulocytes in response to trauma and infection (and hence a fall in the proportion of mononuclear leukocytes). Total leukocyte ascorbate is not a useful index of vitamin C status without a differential white cell count. 

Absorption, Transport, and Excretion. The vitamin is absorbed through the mouth, the stomach, and predominantly through the distal portion of the small intestine, and hence, penetrates into the bloodstream. Ascorbic acid is widely distributed to the cells of the body and is mainly present in the white blood cells (leukocytes). The ascorbic acid concentration in these cells is about 150 times its concentration in the plasma (150,151). Dehydroascorbic acid is the main form in the red blood cells (erythrocytes). White blood cells are involved in the destmction of bacteria. 

Macrocytic anemias are characterized by increased mean corpuscular volume (110 to 140 fL). One of the earliest and most specific indications of macrocytic anemia is hypersegmented polymorphonuclear leukocytes on the peripheral blood smear. Vitamin B12 and folate concentrations can be measured to differentiate between the two deficiency anemias. A vitamin B12 value of less than 150 pg/mL, together with appropriate peripheral smear and clinical symptoms, is diagnostic of vitamin B12-deficiency anemia. A decreased RBC folate concentration (less than 150 ng/mL) appears to be a better indicator of folate-deficiency anemia than a decreased serum folate concentration (less than 3 ng/mL). 

The animals treated with 200, 400, and 800 lU A showed a healing effect of vitamin A on the cornified vaginal epithelium as early as 2 days after starting the experiment. In the smear of all concentrations, almost exclusively leukocytes — indicating a successful healing and mucosal regeneration — with only sporadic epithelial cells and squamous cells... 

There is no specific storage organ for ascorbate apart from leukocytes (which account for only 10% of total blood ascorbate), the only tissues showing a significant concentration of the vitamin are the adrenal and pituitary glands. Although the concentration of ascorbate in muscle is relatively low, skeletal muscle contains much of the body pool of 5 to 8.5 mmol (900 to 1,500 mg) of ascorbate. 

Table 13.2 Plasma and Leukocyte Ascorbate Concentrations as Criteria of Vitamin C Nutritional Status...

An increased incidence of infection, even sepsis after intramuscular injection, as an adverse effect of megadose vitamin E therapy in very low birth weight infants was first reported in Japan in 1986 (SEDA-12, 330). In a review of the literature in 1992 it was concluded that pharmacological serum concentrations of vitamin E might predispose premature infants to infectious complications, possibly caused by an inhibitory effect of vitamin E on the formation of superoxide anion in leukocytes (27). 

More commonly, certain types of cells from blood samples may be obtained and can provide useful inforrna-tion. For example, red cell folate is commonly used as a marker of folate status, and leukocyte vitamin C is a better marker of vitamin C status than plasma concentration. Because of the difficulty of preparation of pure populations of cells, cellular measurements are usually only used within a research environment. 

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