based on dietary assessment should be confirmed by other measures, especially when a high likelihood of inadequacy is suspected.
For example, a 30-year-old woman who consumes an average of 55 mg/day of vitamin C from her food and takes a multiple vitamin four times a week containing 60 mg of vitamin C would average 89 mg/day (55 mg + [60 mg × 4/7]). Thus, her diet alone would put her at high likelihood of inadequacy, since it is below the EAR of 60 mg/day. Addition of the supplement, however, would add up to a sum on average above the RDA of 75 mg/day for adult women, thus suggesting little likelihood that intake is inadequate if the dietary assessment represents her true usual intake.
For vitamin C, vitamin E, and selenium, Adequate Intakes (AIs), rather than EARs or RDAs, have been set only for infants. By definition and observation, healthy infants who are exclusively fed human milk for the first 6 months of life by apparently healthy mothers are consuming an adequate amount of these nutrients. Infants who are consuming formulas with a nutrient profile similar to human milk (after adjustment for differences in bioavailability) for these three nutrients are also consuming adequate levels. In the case where an infant formula contains a lower level of these nutrients than human milk, the likelihood of nutrient adequacy for infants consuming this formula cannot be determined as data on infants at lower concentrations of intake are not available for review.
The Tolerable Upper Intake Level (UL) is used to determine the possibility of overconsumption of a nutrient. If an individual's usual nutrient intake remains below the UL, there is little risk of adverse effects from excessive intake. At intakes above the UL, the risk of adverse effects increases. However, the intake at which a given individual will develop adverse effects as a result of taking large amounts of a nutrient is not known with certainty. For example, an individual consuming supplements of vitamin C that exceed 2,000 mg/day may be at increased risk of adverse effects. In the case of vitamin C, the first adverse effects are osmotic diarrhea and gastrointestinal disturbances. It should be noted that there is no established benefit for presumably healthy individuals in consuming amounts of nutrients that exceed the RDA or AI.