Determining micronutrient requirements and reference intakes
THE CONTEXT
Nutrient adequacy lies between intakes that cause deficiency and intakes that exceed metabolic capacity and cause toxicity.
Assessing requirements
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An adequate intake supports normal health and maintains metabolic integrity.
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In depletion/repletion studies, participants are deprived of a nutrient until a metabolic change develops, then receive the nutrient until the abnormality normalizes.
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Requirements vary between individuals even after adjustment for body size or energy expenditure; the source describes variation of up to 25% around the mean.
Setting reference intakes
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If requirements follow a normal distribution, the interval from the mean minus two standard deviations to the mean plus two standard deviations includes 95% of individual requirements.
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Reference or recommended intakes are set at the average requirement plus two standard deviations, meeting or exceeding the requirements of 97.5% of the population.
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Dietary assessment requires a reference intake that protects against deficiency while avoiding toxicity.
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Published recommendations differ because authorities interpret available evidence differently and newer publications may incorporate additional experimental data.