Serum retinol, concentration

The mean initial serum retinol concentration derived from the 161 children was 0.74 0.46 pmol/liter. Fourteen children (8.7%) exhibited a vitamin A deficiency defined by extremely low serum retinol concentration <0.35 pmol/liter and 78 children (48%) revealed marginal deficiency as indicated by low serum concentrations (<0.70 pmol/liter). Serum retinol concentration was not different in the study- and control group prior to inhalation (Fig. 5.3). 

Vitamin A Both vitamin A (= retinol) and A2 (= 3-dehydroreti-nol) occur in nature. Like their derivatives, they are classed under the umbrella term axerophtol. The major provitamin is p-carotin. Vitamin A is stored as a lipoglycoprotein complex in the fat-storing cells of the liver. It is released when necessary by being coupled with a retinol-binding protein (RBP) and is then transported to the cells which require vitamin A. In the case of zinc deficiency the rate of RBP synthesis is markedly increased, and as a result serum retinol concentration is reduced. Retinol deficiency can be compensated by zinc substitution. The daily requirement is approx. 1 mg. (7, 36)... 

Alcohol may also act indirectly by causing liver disease, which in turn can affect the capacity of the liver to export vitamin A, thereby enhancing its local toxicity. In alco-hoUcs the carrying capacity of retinol binding protein was increased, even in those with low serum retinol concentrations (97). In such cases, caution in the amount of vitamin A used for therapy is recommended. Similarly, diets that are severely deficient in protein can affect the capacity of the liver to export vitamin A and enhance its hepatotoxicity. 

Jalal, F., Nesheim, M.C., Agus, Z., Sanjur, D., and Habicht, J.P. 1998. Serum retinol concentrations in children are affected by food sources of beta-carotene, fat intake, and antehelminthic drug treatment. Am. J. Clin. Nutr. 68, 623-629. 

Even when the storage of samples is satisfactory, changes in serum retinol concentrations that may be indicative of, or result from, specific diseases must be interpreted with caution. Factors other than the process studied that may influence the results are (1) The coefficient of variation for intraassay analyses, even at best, is 2-5%, and for interassay data is often 5-10% thus, small observed differences between groups may not be truly significant. (2) Reference standards... 

Limits of detection for absorbance detectors (325 nm) with conventional (5 qm particle size) C18 columns and methanol water mobile phases are typically 0.35 pmol (0.1 ng) at a 5 1 signal noise ratio. Even low serum retinol concentrations as found in vitamin A deficiency (0.35 to 0.7 iM, i.e., 10 to 20 Ag/dL) require sample volumes of only 1 pL Nonetheless, fiuorescence detection can give even lower limits of detection (0.07 pmol, 20 pg in tear fluid (111) 5-pL sample sizes have been used for routine plasma assays (112). Electrochemical detection has also been used for simultaneous analysis of retinol and tocopherol (113,114). Microbore columns and smaller packing particle sizes could give improved limits of detection (115,116) but require low-dispersion fittings and detector cells. The requirements for plasma retinol quantitation are not so stringent that use of these techniques has become popular. 

The most commonly used biochemical indicator of vitamin A status in the past has been the measurement of serum retinol concentrations. Although the distribution of such values in a population can be instructive, serum retinol values are homeostatically controlled over a wide range of total body reserves, are depressed during fever and infections, and are adversely affected by inadequate intakes of other nutrients, such as protein and zinc. Thus, serum retinol concentrations are not very sensitive indicators of vitamin A status, unless they are very low (<0.35 pmol/1, i.e.<10 pg/dl) or are clearly adequate (>1.05 pmol/1 in children, >1.40 pmol/1 in adults). As a result, the response tests, RDR and MRDR, are increasingly used, which combine serum retinol concentrations with the individual s response to a small oral dose of a retinoid. 

Figure 4 Global geographic distribution of xerophthalmia (X, all clinical stages) and vitamin A deficiency (VAD, serum retinol concentrations <0.70pmol/l) in preschool-aged children. From West KP Jr (2002) Extent of vitamin A deficiency among children and women of reproductive age. Journal of Nutrition.

A number of studies have reported low serum concentrations of retinol and high concentrations of /3-carotene in patients with insulin-dependent diabetes melUtus. Krill and coworkers (1997) showed that up to one-third of nondiabetic first-degree relatives of patients with diabetes also showed a low serum retinol carotene ratio, implying a genetic predisposition to low activity of carotene dioxygenase, possibly associated with insuUn-dependent diabetes. 

There are also changes in the binding proteins in plasma as a result of the disease process. Since serum albumin falls in association with any acute iUness, this inevitably leads to a fall in plasma zinc concentration. Similarly a reduction in retinol-binding-protein concentration as part of the APR or protein malnutrition also leads to a fall in serum retinol levels, whatever the amount of retinol stores within the liver. 

Prealbumin is the transport protein for thyroxine and a carrier for retinol-binding protein. The body s content of prealbumin is low (10 mg/kg of body weight), and it has a very short biologic half-fife (I to 2 days). Prealbiunin may be reduced in as few as 3 days after calorie and protein intake is significantly decreased, or when hypercatabolism or severe metabolic stress (tramna or bmns) is present. Because of its short half-life, it is most useful in monitoring the shortterm, acute effects of nutrition support. As with ALB and TFN, sermn prealbumin concentrations are depressed in those with liver disease due to decreased hepatic synthesis. Increased serum prealbumin concentrations have been noted in patients with renal disease due to impaired renal excretion. 

A. Specific levels. Serum vitamin A (retinol) or carotenoid assays may assist in the diagnosis of hypervitaminosis A. Levels of 25-hydroxy vitamin D are useful in assessing excessive intake. Other serum vitamin concentration measurements are not useful. 

AeberH, 1., Biebinger, R., Lehmann, R. et al. 2007. Serum retinol-binding 4 concentrations and its ratio to serum retinol are associated with obesity and metabolic syndrome components in children. J Clin Endocrinol Metab 92 4359-4365. 

Cban, T. R, Tsai, Y. C., Wu, C. H. et al. 2011. Tbe positive correlation between cord serum retinol-binding protein 4 concentrations and fetal growth. Gynecol Obstet Invest 72 98-102. 

Cbang, Y. H., Lin, K. D., Wang, C. L. et al. 2008. Elevated serum retinol-binding protein 4 concentrations are associated with renal dysfunction and uric acid in type 2 diabetic patients. Diabetes Metab Res Rev 24 629-634. 

A. Epidemiology This section reviews studies that relate dietary intake of vitamin A or serum concentration of retinol to the incidence of cancer. These data suggest an inverse relation between cancer risk and low intake of vitamin A or low serum retinol. 

Butler JC, Havens PL, Sowell AL, Huff DL, Peterson DE, Day SE, Chusid MJ, Bennin RA, Circo R, Davis JP (1993) Measles severity and serum retinol (vitamin A) concentration among children in the United States. Pediatrics 9 1176-1181... 

De Pee, S. et al.. Orange fruit is more effective than are dark-green, leafy vegetables in increasing serum concentrations of retinol and (3-carotene in school children in Indonesia, Am. J. Clin. Nutr, 68, 1058, 1998. 

The presence of a certain number of amino acids is significant for the restitution of the immune system s cells, interferon synthesis process and other factors realization of the immune defense system. The decrease of full-form protein consumption is one of the causes of secondary immune-deficiency states. The significance of ascorbic acid presence for the immune system is supported by the fact that its concentration in the neutrophil granulocytes is 150 times higher than in the blood serum. The significance of retinol s and carotenoids role is supported in the cases of cell differentiation, where DNA synthesis increase, and proliferation decrease thus stabilizing the organism when under infection. 

In another study (Moriel et al., 2002), 11 patients with mild essential hypertension were compared with 11 healthy subjects for water- and lipid-soluble antioxidants and the concentrations of nitric oxide derivatives in the plasma. A significant reduction in plasma lycopene was observed in the hypertensive patients compared to the normal subjects. Similar reductions in ascorbate, urate, and (3-carotene were also observed in this study. However, there were no differences in the nitrous oxide derivatives between the two groups. Hypertension and lymphatic circulation impairment are associated with liver cirrhosis. When patients with liver cirrhosis were compared to healthy matched controls, a significant reduction in serum lycopene, other carotenoid antioxidants, retinol, and oc-tocopherol were observed in the cirrhotic patients. Based on these observations, the authors recommend thorough screening for the antioxidants and improved diet in the... 

C32. Comstock, G. W., Alberg, A. J., and Helzlsouer, K. J., Reported effects of long-term freezer storage on concentrations of retinol, beta-carotene, and alpha-tocopherol in serum or plasma summarized. Clin. Chem. 39, 1075-1078 (1993). 

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