Reference Intakes of Vitamins

Notwithstanding the problems involved in determining requirements for vitamins, most nationed authorities (as well as the United Nations FAO/WHO and the Europetm Commission) publish, and periodically revise, tables of recommended inttikes of nutrients or dietary reference vedues. 

As shown in Table 1.9, a number of terms are used Recommended Dtuly (or Dietary) Inttike (RDl), Recommended Dietary (or Daily) Amount (RDA), Reference or Recommended Nutrient Intake (RNl), and Population Reference Inttike (PRl). AU have the same statistical basis, and all tue defined as an intake of the nutrient that is adequate to ensure that the requirements of essentitdly all healthy people in the specified population group tue met. The 2001FAO/WHO report introduced the term protective nutrient intake - an tunount greater them the reference inttike that may be protective against specified hetdth risks of public health importemce. 

There is, in fact, little evidence that requirements do follow a Gaussian distribution theU.S./Canadiantables (Institute ofMedicine, 1997,1998,2000,2001) note this, and state that when the distribution is skewed the 97.5th percentile ctm be estimated by transforming the data to a normal distribution. Where the standard deviations from different studies are inconsistent, the U.S. /Ctmadian tables determine the RDA on the basis of 1.2 x average requirement. This assumes a coefficient of vtuiation of 10%, which is based on the known varitmce in based metabolic rate. 

It is apparent from this discussion that reference intake figures eue intended for use in populations emd communities, and do not apply to individueds. An individual might have a requirement anywhere within the range, emd therefore 

RDA Recommended Dietary Allowances U.S., 1941 The name was deliberately chosen to allow the possibility of future modification of the values and was not intended to carry any connotation of minimum or optimal requirements. 

As shown in Tables 1.5-1.8, reference intakes published by different authorities show considerable differences. Some of the reasons for this are apparent from the discussion above different criteria of adequacy may be applied by the members of different expert committees, and the estimation of average requirements and, hence, reference intakes requires a considerable exercise of judgment to interpret the relatively small body of scientific literature. Historically, tables of reference intakes were based on requirements to prevent deficiency disease, or subclinical signs of inadequacy increasingly, as evidence accumulates, the emphasis is on requirements to promote optimum health rather than to prevent deficiency. 

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Table 1.6 Population Reference Intakes of Vitamins, European Union, 1993... 

Indices of Vitamin E Nutritional Status Reference Intakes of Vitamin K Indices of Thiamin Nutritional Status Reference Intakes of Thiamin Tissue Flavins in the Rat Urinary Excretion of Riboflavin Metabolites... 

Vitamin Be-Responsive Inborn Errors of MetaboUsm Indices of Vitamin Bg Nutritional Status Reference Intakes of Vitamin Bg Adverse Effects of Hyperhomocysteinemia Indices of Folate and Vitamin B12 Nutritional Status... 

Vitamin C-Dependent 2-Oxoglutarate-linked Hydroxylases Plasma and Leukocyte Ascorbate Concentrations as Criteria of Vitamin C Nutritional Status 13.3. Reference Intakes of Vitamin C... 

The reference intakes of vitamins and minerals published in the USA, UK and European Union are shown in Tables 11.1—11.3-... 

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