Highest Observed Intake: definition, regulatory uses and provisional values.

For nutrients and related substances, the Tolerable Upper Intake Level (UL) has become the internationally accepted risk assessment method. The major limitation of the UL method as applied by authoritative groups thus far is that no UL has been set for nutrients without established adverse effects. In contrast to the limitations inherent in the UL method, an alternative approach is available; it identifies a risk assessment value termed the Highest Observed Intake (HOI). In the absence of a UL, the HOI is the highest intake with adequate data to show, with acceptable confidence, the absence of adverse effects up to that intake. With this concept defined and accepted in a report by the authoritative international organizations FAO and WHO, a complete risk assessment for the nutrients and related substances would have to identify UL values for those with known adverse effects and HOI values for those without known adverse effects. The need for the HOI concept and value is illustrated by the unjustified policy and regulatory actions taken in relation to vitamin B12. Regulatory utility is explained and tentative HOI values are identified for several vitamins and non-essential nutrients. Endorsement of the concept and development of HOI values by authoritative bodies is likely to be required for broad acceptance and use.