Presenter: Robert M. Russell
The Institute of Medicine’s (IOM’s) conceptual model for the UL (see Figure O-1 in the Overview) involves determination of the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Robert Russell provided a brief review of the derivation of a UL and the sources of uncertainty and then focused on how three different expert groups arrived at different conclusions when they determined the upper levels1 for vitamin A, beta carotene, vitamin B6, and zinc. He concluded his presentation with a list of the kinds of data needed to improve the determination of upper levels for these four nutrients.
The process of deriving an upper level typically involves the identification of a critical data set; the identification of a critical toxic effect (the endpoint, a no-observed-adverse-effect level [NOAEL] or a lowest-observed-adverse-effect level [LOAEL]); and the derivation of an uncertainty factor, which typically is less than 10 for nutritional risk assessment. By using this approach, the upper level is obtained by the following formula:
Therefore, the larger that the uncertainty factor is, the lower that the value of the upper level is.
The process of assigning an uncertainty factor has been somewhat subjective. Factors that have contributed to assigning a larger uncertainty factor include extrapolation of the findings of studies with animals to