Assessment of Vitamin Nutritional Status

The same criteria used to define requirements ctm also be used to assess vitamin nutritional status. 

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

Determination of plasma, urine, or tissue concentrations ofvitamins and their metabolites. These methods depend on comparison of an individual or group with the population reference range, which is normally taken as the 95% confidence intervjd twice the standard deviation about the mean value. By definition, 5% of the normal healthy population will lie outside the 95% reference range. 

Metabolic loading tests and the determination of enzyme saturation with cofactor measure the ability of an individual to meet his or her idiosyncratic requirements from a given intake, and, therefore, give a nearly absolute indication of nutritional status, without the need to refer to population reference ranges. A number of factors other than vitamin intake or adequacy can affect responses to metabolic loading tests. This is a pardculai- problem with the tryptophan load test for vitamin Be nutritional status (Section 9.5.4) a number of drugs can have metabolic effects that resemble those seen in vitamin deficiency or depletion, whether or not they cause functioned deficiency. 

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