Recommended Nutrient Intakes
For many vitamins and minerals, scientific committees have established recommended intakes.
A Requirement is the level of nutrient that an individual requires for efficient functioning.
A Recommended Intake is the level of a nutrient that is set to ensure that the majority of a healthy population will be meeting their individual requirement. These are referred to as Recommended Dietary Allowances (RDA), Recommended Nutrient Intakes (RNI) and Reference Nutrient Intakes (RNI). These essentially mean the same thing.
The recommendations are often age and sex specific and take into account different physiological states (i.e. pregnancy and lactation).
Principle
The requirements of nutrients depend on age, sex, body size and composition, energy expenditure, physiological state, and digestion, storage capacity and metabolism of nutrients. The measurement of the requirements for a particular nutrient in a group of individuals generates a distribution of requirements based on the latter variables. The mean of this distribution represents the average requirement (sometimes referred to as the estimated average requirement (EAR)). The standard deviation is the measure of variability in requirement. Scientific committees have generally set the recommended nutrient intake at the estimated average requirement plus 2 standard deviations. See diagram.
Therefore recommended dietary allowances are defined as "amount of a nutrient which should be provided per head of a population group, if the needs of practically all people in that population are to be met.
This means that the RNI exceeds the needs of all but 2-3% of the population. They are not minimum requirements, they have a large safety margin.
The UKst1:place> has developed Dietary Reference Values (DRV). Again they have estimated the average requirements (EAR) and the Reference Nutrient Intake (RNI) is 2 standard deviations above the EAR. They have also developed a Lower Reference Nutrient Intake (LRNI), which is 2 standard deviations below the EAR. They have also set a Safe Upper Limit for nutrients, above which, an habitual intake may increase the risk of adverse effects.
The USA and Canada have recently reviewed their dietary reference values. They have estimated the average requirements (EAR) and the Reference Nutrient Intake (RNI) is 2 standard deviations above the EAR. They have also set Upper Tolerable Intake Levels (UL). A chronic intake above these levels may increase the risk of adverse effects.
In setting their Reference Nutrient Values, the USA/Canada have also taken into account whether consuming more of a particular nutrient protects against chronic disease.
There is also a setting known as an "Adequate Intake" or "Acceptable Intake" (AI). The AI is set instead of the RNI if there is insufficient evidence available to calculate an EAR. Often there is insufficient data to determine the distribution and average requirement for a nutrient in a population and so the AI is determined by examining observed mean intakes of a nutrient in a group of healthy individuals or derived from estimates based on limited experimental data. For example AI's are set for nutrient intakes of healthy term infants who are exclusively breast fed.
Interpreting nutrient intakes
Habitual intakes above the RNI are almost certainly adequate for most individuals.
Habitual intakes below the LRNI are almost certainly inadequate for most individuals.
NB It is important to recognise that if an individual's intake is below the RNI, they should not be classified as "deficient" or "inadequate" because of the large safety margin. We can say that the more the habitual intake of an individual falls below the recommended intake and the longer the duration of the low intake, the greater the risk of nutrient deficiency for that individual.
Assessing Individual Diets
When assessing diets for individuals, we can say that if habitual intake is below the LRNI it is likely that the individual will not be consuming sufficient amounts of the nutrient to maintain function. If the intake is above the RNI, then it is extremely likely that the individual will be consuming sufficient intakes of the nutrient. If the intake lies between the LRNI and the RNI, then the chances of the diet being inadequate fall as the intake approaches the RNI.
When an individual's intake lies between the LRNI and the RNI, it is impossible to say with any certainty whether an individuals intake is adequate or not, without some biological measure for that individual.
In general, we can say:
- The closer an intake is to the RNI, the less likely that their intake is inadequate.
- Observed intake between the EAR and the RNI probably need to be improved.
- Intakes below the EAR very likely need improvement
- The closer the intake is to the RNI, the more likely that the intake is inadequate
In summary, the Dietary Reference Values (DRV) only provides a guide to dietary adequacy and should be applied to individuals with utmost caution.
Assessing Diet of Groups of Individuals
If good dietary data is collected, some information on percentiles of intake may be available.
It may be possible to say that "x" percent of the group had intakes below the RNI. If "x" is zero then the risk of deficiency in the whole group is extremely small. As "x" increases the risk of deficiency in the group increases.
However, because by definition, the RNI exceeds the requirements of most people within the population, it is not really appropriate to determine the adequacy of a group's intake. It would be more appropriate to use the EAR to assess the prevalence of inadequate intake of a nutrient from usual intake data of a group.
Remember: The usefulness of comparison of nutrient intakes with the dietary reference values is dependent on the quality of dietary data collected.
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