Uses of Dietary Reference Intakes

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The DRIs consist of four components. Each type of reference value is calculated from daily intakes averaged over time (usually one or more weeks). The surveys include, but are not limited to, (1)random selection of healthy individuals and asking them to either report what they have eaten or to maintain food diaries, (2) monitoring overall food production and consumption, and (3) correlating a defined population's health status with the group's food intake. Sometimes the results from the surveys are correlated with the type of assays listed in Table 8.2. The four Dietary Reference Intakes are: Estimated Average Requirement (EAR). The EAR is the intake that meets the estimated nutrient need of 50% of the individuals in that group (i.e., infants, children, adult males, adult females, pregnant women, nursing women, the elderly, etc.). It is used to evaluate the adequacy of nutrient intakes of population groups and for planning intakes for group. It can be used in diet planning. The EAR is based on a median rather than a mean.

2 Recommended Dietary Allowance (RDA). The RDA is the intake that meets the nutrient need of almost all (97-98%)individu-

Table 8.1 Causes of Nutrient Deficiencies




Inadequate ingestion usually from a poor diet u>

Inadequate absorption

Economic deprivation Self-imposed reducing diets


Diseased intestinal tract

Mineral oil laxatives, which may dissolve the oil-soluble vitamins

Ion exchange resins (colestipol, Colestyramine), which complex with the bile salts and can interfere with the absorption of the oil-soluble vitamins Aluminum antacids can complex with some of the vitamins and, when used chronically, most definitely can cause hypophosphatemia Cystic fibrosis, which can cause fat malabsorption (steatorrhea) attributed to inadequate production of pancreatic lipases

Inability to purchase adequate amounts and variety of food.

A 1200 calorie diet professionally selected from the four major food groups (dairy, fruits and vegetables, grains, and meat) containing no fried food nor added sugar has been considered the least amount of food not requiring a vitamin supplement.

This usually is attributed to loss of appetite from such conditions as cancer chemotherapy, depression, and eating disorders.

Examples include chronic inflammatoryconditions such as Crohn's disease and parasites.

This could include retinol, cholecalciferol/ergocalciferol, a-tocopherol, vitamin K from food.

A vitamin supplement can be taken 1 h before or 2 h after taking the resin.

Aluminium antacids are no longer commonly used.

This could include retinol, cholecalciferol/ergocalciferol, a-tocopherol, vitamin K from food, all of which are more readily absorbed when they can be part of a normal mixed micelle process that occurs with lipid digestion and absorption

Increased requirements above the recommended daily allowances (RDA)

Chronic intake of alcohol (alcoholism)

Drug-vitamin interactions

Reference dietary indices are based on an average population performing average duties. Increased physical activity or medical needs make these people statistical outliers beyond the requirements of the "average" healthy population group.

Ethyl alcohol can interfere with the uptake, processing, or storage of vitamins.

(MSUD), which will respond to thiamine (vitamin Bx) supplements, and homocystinuria, which will respond to pyridoxine (vitamin B6). The mutation lies with apoenzyme such that the equilibrium between the apoenzyme and the coenzyme lies to the left. To push the reaction to the right requires additional coenzyme.

These can interfere with vitamin processing in the intestinal tract, tie up the vitamin preventing it from being used, or possibly promote elimination of the vitamin. Examples include: isoniazid-pyridoxine, phenobarbital-cholecalciferol, methotrexate-folic acid, phenytoin-folic acid.

Individuals performing more strenuous activities requiring additional intake of calories also will require more nutrients including vitamins.

Vitamin and caloric requirements increase for patients experiencing debilitating illness, including severe burns, major surgeries, and malignancies. Nutritional assessments are becoming a more common part of medical treatment.

The two most common vitamin deficiencies seen in patients chronically consuming alcohol are folic acid and thiamine.

Table 8.2 Methods for Estimating Vitamin Requirements


Determination Methodology

Retinol (vitaminA)

Dark adaption test Pupillary response test Plasma retinol concentration Relative dose response

Calciferol (vitamins D2

and D3) a-Tocopherol (vitamin E)

Vitamin K

Serum 25(OH)D2 or D3

Lipid peroxidation markers Plasma a-Tocopherol concentration Prothrombin time

Thiamine (vitamin Bx)

Riboflavin (vitaminB2)


Factor VII

Plasma or serum phylloquinone concentration Urinary y-carboxyglutamyl residues Erythrocyte transketolase activity Urinary thiamine excretion Erythrocyte thiamine concentration Erythrocyte glutathione reductase activity Erythrocyte flavin

Urinary riboflavin excretion Urinary excretion

Plasma concentration

Erythrocyte pyridine nucleotides


Considered reasonably sensitive.

Data do not exist relating pupillary threshold sensitivity to retinol intake.

Insensitive to liver stores.

An initial plasma concentration is determined followed by a second concentration a defined time after administration of a small dose of retinol. The ratio is proportional to the liver stores of retinol.

This is considered a more accurate indicator of vitamins D status as compared to serum vitamins D, or l,25(OH)2D.

They are not specific to vitamin E.

It does not seem to correlate with daily intake, but there is a linear relationship seen in tocopherol-depleted subjects.

It is used to assess patients on Coumadin anticoagulant therapy, but does not appear to be a reliable measure of vitamin K status in otherwise healthy subjects.

Even though factor VII only has a 6-h half-life, it does not appear to be reliable.

This does respond to changes in dietary intake within 24 h.

This is considered promising.

This is considered the most accurate.

This method also is considered good.

It is not as widely used.

It is the most common assay.

Some question the sensitivity of this test because the difference between adequacy and inadequacy is small.

Care must be exercised with the size of the dose and method of administration.

N1-Methylnicotinamideand ^-methyl^-pyridone-S-carboxamide are the two metabolites that are considered sensitive measures of niacin status.

JV1-Methyl-2-pyridone-5-carboxamide plasma levels provide an indication of low niacin intake by dropping below detection limits.

Erythrocyte NAD levels may replace measuring metabolites found in the urine.

Vitamin Bfi family

Plasma pyridoxal phosphate Erythrocyte and total blood pyridoxal phosphate Urinary pyridoxic acid Various erythrocyte transaminases

Tryptophan catabolites

Pantothenic acid

Biotin Folic acid

Plasma homocysteine Urinary excretion Blood levels Urinary excretion Erythrocyte folate

Plasma homocysteine

Serum folate

Vitamin Bi g (cobalamin)

Urinary folate Hematological status Hematological response

Serum or plasma vitamin B„

Methylmalonic acid



Ascorbic acid (vitamin C)

Antioxidant functions

Cellular DNA damage Urinary markers

It changes slowly in response to changes in vitamin intake.

There may be racial differences because of lower kinase activity.

It tends to reflect recent vitamin intake rather than general vitamin status.

Aspartate and alanine transaminases have been studied most extensively. There is a lack of consensus regarding their usefulness as indicators of vitamin B, status.

Although useful, some of the reactions affected changes in steroid hormone status.

See discussion in the vitamin B^ section.

It is strongly dependent on intake.

There is poor correlation with urinary excretion values.

There is a correlation with induced deficiencies caused by eating raw egg white.

Only the developing erythrocyte takes up folate. Therefore, this test is an indicator of long-term status and not a measure of immediate changes in folate status.

There is no question that elevated homocysteine decreases with folate administration. There is not enough information to support its use for determining DRIs.

A measure of dietary folate intake, although it is not considered a reliable measure of folate status.

This test may underestimate folate needs.

Characteristic megaloblastic anemia develops late in folic acid deficiency.

These are the typical hemoglobin, hematocrit, and erythrocyte counts. Partial responses are of limited values.

A problem is that serum values may be maintained at the expense of tissue stores.

Studies need to be done to see whether it will correlate with vitamin B12 status.

This can be elevated in folate and vitamin B, deficiencies.

This protein is responsible for receptor-mediated uptake of B„ into cells. Further work needs to be done before it is adapted for routine clinical use.

A variety of markers have been evaluated including LDL, VLDL, malondialdehyde, hydroxynonenal, and reduced glutathione.

These have not proved useful for estimating ascorbate requirements.

Oxidized DNA is nonspecific.

als in that group. The RDA are the values found on most vitamin products. They vary depending on whether the product is intended for infants, children, or adults. The RDAs can function as a guide to achieve adequate nutrient intake. By themselves, they are not generally recommended for diet planning for specific groups of individuals. Diet planning must take into account extensive physical activity, type of body build including lean vs. adipose tissue, general lifestyle, and so forth. If the sampling and endpoints are well defined, the RDA can be calculated from the EAR.

RDA = EAR + 2SDear where SDEAR is the standard deviation above the EAR.

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