Vitamin biochemical assessment

Biochemical assessment of trace element, vitamin, and essential fatty acid deficiencies should be based on the nutrient s function, but few practical... 

Biochemical criteria of vitamin adequacy and methods for biochemical assessment of nutritional status can be divided into the following two distinct groups ... 

Sauberlich HE, Canham JE, Baker EM, Raica N Jr, and Herman YF (1972) Biochemical assessment of the nutritional status of vitamin B 6 in the human. American Journal of Clinical Nutrition 25, 629-42. 

As with the other B vitamins that act as coenzymes biochemical assessment of vitamin Bg can, be made by direct chemical analysis of the vitamer or its metabolites, or by functional means. Measurements that have been used are PLP in plasma or red cells, its metabolite 4 PA in urine or plasma, the activity and activation coefficient of the red cell aminotransferases (aspartate and alanine), and the tryptophan load metabolite excretion test. As no single marker adequately reflects status, a combination of these markers olfers the best approach. 

A comprehensive nutrition assessment must include an evaluation of possible trace element, vitamin, and essential fatty acid deficiencies. Because of their key role in metabolic processes (as coenzymes and cofactors), a deficiency of any of these nutrients may result in altered metabolism and cell dysfunction, and may interfere with metabolic processes necessary for nutritional repletion. The evaluation of single-nutrient-deficiency states includes an accurate history to identify symptoms and risk factors that may indicate deficiency or predispose the patient to developing a deficiency state. A focused physical examination for signs of deficiencies and biochemical assessment to confirm a suspected diagnosis also should be done. Ideally, biochemical assessment would be based on the nutrient s function (e.g., metalloenzyme activity) rather than simply measuring the nutrient s serum concentration. Unfortunately, few practical methods to assess micronutrient function are available currently, and most assays measure serum concentrations of the individual nutrient. 

We have evaluated the biochemical response of mice to ADR treatment when fed either Mn-sufficient or -deficient diets. In addition we varied the level of vitamin E to assess the influence of a combined deficit of dietary antioxidants on ADR toxicity (33). 

Assessment of vitamin A nutritional status depends on the biochemical criteria shown in Table 2.3. 

Sokoll LJ and Sadowski JA (1996) Comparison of biochemical indexes for assessing vitamin K nutritional status in a healthy adult population. American Journal of Clinical Nutrition 63, 566-73. 

Mount JN, Heduan E, Herd C, Jupp R, Kearney E, Marsh A. Adaptation of coenzyme stimulation assays for the nutritional assessment of vitamins Bl, B2 and B6 using the Cobas Bio centrifugal analyser. Ann Clin Biochem 1987 24 (Pt l) 41-6. 

In summary Because of the short time required to develop biochemical evidence of a deficiency of many water soluble vitamins, it would appear that these nutrients should be included from the initiation of any complete parenteral nutrition program. If MVI (USV Pharm.) is used, care should be taken to insure that the patient does not receive excessive amounts of the fat soluble vitamins. Ideally there should be separate preparations of the water and fat soluble vitamins. Unless these solutions are made available for study, the actual requirement for each vitamin will remain difficult to assess. In this regard, it is quite disturbing that recently the FDA, with disregard for the needs of the patients whose lives may be saved by total parenteral nutrition, has placed severe restrictions on the use of intravenous vitamin preparations. 

Methyl malonic acid (MMA) reduction. Because the bioehemieal pathway that reduees MMA levels in the blood uses only vitamin B12, lowering MMA levels is a test speeific for vitamin B12 activity. Although it is not known for certain, it is likely that this biochemical pathway is an integral part of the function of vitamin B12 in nerve tissue. Thus, if food lowers MMA levels, it can be assumed to provide full vitamin B12 activity. Similarly, the bioavailability of vitamin B12 in lyophilized purple liver was assessed by MMA exeretion to find total vitamin B12 and vitamin B12 analogue eontents in the liver. 

Thiamine, or vitamin Bi, is a water-soluble compound which is rapidly broken down by moist heat in neutral or alkaline solutions into its constituent pyrimidine and thiazole rings. The ready destructability of thiamine is important in human nutrition, since much may be lost in the preparation of food. Some of the biochemical methods used in evaluating thiamine nutrition are based on reactions with the thiazole and pyrimidine portions of the thiamine molecule. The thiochrome method is widely used in assaying biological materials for thiamine, while determination of the urinary excretion of pyramine (a pyrimidine-like compound) has been used to assist in assessment of nutritional status. 

All of the studies that suggested that oral contraceptives cause vitamin deficiency used the tryptophan load test (section 11.9.5.1). When other biochemical markers of status were also assessed, they were not affected by oral contraceptive use. Furthermore, most of these studies were performed using the now obsolete high-dose contraceptive pills. 

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. 

Thiamin is the least stored of all the vitamins. The adult human body contains approximately 30 mg. Of the thiamin stored in the body, about 80% is thiamin pyrophosphate, about 10% is thiamin triphosphate, and the remainder is thiamin monophosphate. The liver, kidneys, heart, brain, and skeletal muscles have somewhat higher concentrations than the blood. If the diet is deficient, tissues are depleted of their normal content of the vitamin ini to 2 weeks, so fresh supplies are needed regularly to provide for maintenance of tissue levels. Body tissues take up only as much thiamin as they need with the need increased by metabolic demand (fever, increased muscular activity, pregnancy, and lactation) or by composition of the diet (carbohydrate increases the need for thiamin, while fat and protein spare thiamin). Because thiamin is water soluble, most of the vitamin not required for day-to-day use is excreted in the urine. This means that the body needs a regular supply, and that unneeded intakes are wasted. With a well-balanced diet, approximately 0.1 mg is normally excreted every 24 hours. However, the amount excreted in the urine decreases as the intake becomes inadequate and increases as the intake exceeds body needs because of this, the most widely used biochemical method to assess thiamin status in individuals is the measurement of the vitamin in the urine. 

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