If sufficient scientific evidence is not available to establish an EAR and set an RDA, an AI is derived instead. The AI is based on experimentally derived intake levels or approximations of observed mean nutrient intakes by a group (or groups) of apparently healthy people who are maintaining a defined nutritional state or criterion of adequacy. Examples of defined nutritional states include normal growth, maintenance of normal levels of nutrients in plasma, and other aspects of nutritional well-being or general health.

The AI would not be consistently related to the EAR and its RDA even if they could be established. For example, for young infants, the AI is usually based on the daily mean nutrient intake supplied by human milk for healthy, full-term infants who are exclusively fed human milk. For adults, the AI may be based on data from a single experiment (e.g., the AI for choline [IOM, 1998b]), based on estimated dietary intakes in apparently healthy population groups (e.g., the AIs for biotin and pantothenic acid [IOM, 1998b]), or result from a review of data from different approaches (e.g., the AI for calcium, based on calcium retention, factorial estimates of requirements, and limited data on bone mineral density and bone mineral content changes in adult women [IOM, 1997]). The AI is expected to exceed the EAR and the RDA for a specified criterion of nutritional adequacy. When an RDA is not available for a nutrient (since there is no EAR), the AI can be used as the goal for an individual's intake. However, as is explained later in this report, the AI has limited uses in assessment.

The issuance of an AI indicates that more research is needed to determine, with some degree of confidence, the mean and distribution of requirements for that specific nutrient. When this research is completed, it should be possible to replace estimates of AIs with EARs and RDAs.

The UL is the highest level of continuing daily nutrient intake that is likely to pose no risk of adverse health effects in almost all individuals in the specified life stage group (Figure 1-1). As intake increases above the UL, the potential risk of adverse effects increases. The term tolerable intake was chosen to avoid implying a possible beneficial effect. Instead, the term is intended to connote a level of intake with a high probability of being tolerated biologically. The UL is not intended to be a recommended level of intake. Unless