Assessment of Vitamin C Status

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). 

Urinary excretion of ascorbate fails to undetectably low levels in deficiency therefore, very low excretion will indicate deficiency. However, no guidelines for the interpretation of urinary ascorbate have been established, and basal urinary excretion of ascorbate is rarely used in the assessment of status. During depletion/repletion studies, urinary excretion increases before tissue saturation has been achieved (Sauberlich, 1975). 

It is relatively easy to assess the state of body reserves of vitamin C by measuring the excretion after a test dose. A subject whose reserves are saturated will excrete the whole of a test dose of500 mg of ascorbate over 6 hours. A more precise method involves repeating the loading test daily until complete excretion is achieved, thus giving an indication of how depleted the body stores were. 

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A test for assessing the vitamin C status of the body. Ascorbic acid is given orally and its output in the urine is measured. In normal subjects, more of the vitamin will be excreted in the urine, because the tissue stores are already saturated. In deficient patients, less vitamin will be excreted because of its uptake by the tissues. 

Vitamin C status can be assessed by measuring plasma levels or urinary excretion. However, due to practical disadvantages, e.g., quantitative sampling of urine and instability of vitamin C, determination of vitamin C in urine has been mainly replaced by determination of plasma levels. Methods include direct determination by FIPLC, or automated assays based on a derivatization of ascorbic acid forming colored or fluorescent derivatives. While a plasma concentration <11.4p.molH is widely used to characterize deficiency, literature data signifying adequate status vary from >17 to 28.4p.moll. ... 

A water soluble vitamin which cannot be synthesized by man and therefore has to be obtained from the diet. It is found extensively in vegetables and fruit, especially the citrus varieties. Since the vitamin is carried mainly in the leukocytes, its measurement in these cells gives some indication of the vitamin C status of the body. The ascorbic acid saturation test can also be used to assess the vitamin status. The biochemical role of the vitamin is obscure although it does seem to be required for collagen formation. Deficiency of the vitamin causes scurvy, the symptoms of which can be related to poor collagen formation. These include poor wound-healing, osteoporosis (due to bone matrix deficiency), a tendency to bleed (due to deficiences in the vascular walls) and anaemia. 

Suaberhch HE. Vitamin C. In ed. Laboratory tests for the assessment of nutritional status. Boca Raton, EL CRC Press, 1999. 

Van Jaarsveld, P. J., Faber, M., Tanumihardjo, S. A., Nestel, P., Lombard, C. J., and Spinnler Benade, A. J. (2005). 3-carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose response test. Am. ]. Clin. Nutr. 81, 1080-1087. 

Ascorbic acid is an important essential nutrient for the health maintenance of the population. Nevertheless, its importance must not be overestimated. The status assessment of the vitamin in well-nourished populations showed only a small percentage of subjects with an insufficient plasma ascorbic acid concentration. It has been documented that risk factors for the development of an ascorbic acid deficiency exist (e.g., smoking, alcohol use, pregnancy, certain pathophysiological conditions). These deficiencies can, however, be overcome without any problems when the current recommendations on vitamin C intake are fulfilled by the intake of either... 

Vitamin E Status of Humans. As hypovitaminosis E is a rare event (see D), a routine assessment of the vitamin E status in humans is not required but only justified for risk groups (e.g., prematures) and as part of studies on the chemoprevention of diseases presumably involving oxidative stress as an etiological factor, e.g., cancer, atherosclerosis, and cataract. Knowledge about the in vivo fate of vitamin E (see C) will guide in the choice of samples to be analyzed. The most common, easily obtainable biological matrix for the determination of vitamin E and of a-tocopherol in particular is plasma/serum. Plasma levels of Y-tocopherol, which is more abundant in foods, are of little importance except... 

The early method of assessing vitamin C nutritional status was by testing the extent of saturation of the body s reserves by giving a test dose of 500 mg (2.8 mmol) and measuring the amoimt excreted in the urine, fii a subject with high status, more or less all of the test dose is recovered over a period of 5 or 6h. 

Considerable uncertainty and controversy exists concerning the folate requirement for humans. Hie review of data concerning the human folate requirement by the Food and Nutrition Board (1989) suggests that the daily maintenance requirement is 100-200 fig of avaUable folic acid equivalents. The 1989 RDAs were reduced to 200 and 180 fig for adult men and women, respectively, from the previous RDA of 400 on the basis of such evidence (Food and Nutrition Board, 1989). Similarly, the Canadian RDA for folate was set at 3 /ig/kg body wt or 210 fig for a 70-kg individual. These lower RDAs may be inadequate for certain population groups, however (Sauberlich, 1990 Bailey, 1992 McPartlin etai, 1 3). It is currently difficult or impossible to predict the quantitative effect on folate nutritional status of factors such as (a) changes in folate intake, (b) differences in folate bioavailability, (c) effects of pregnancy and lactation on folate requirements, and (d) pharmaceuticals with antifolate properties. In addition, the development of mathematical models would improve our ability to evaluate methods of nutritional status assessment for this vitamin. 

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