Nutrient risk assessment: setting upper levels and an opportunity for harmonization.

Upper levels are estimates of the quantity of a nutrient that can be ingested daily over a lifetime without appreciable risk to health. The approach to establishing upper levels for nutrients, nutrient risk assessment, has derived from the risk assessment of foreign chemicals that are deliberately added to foods, or are in food as contaminants. This process of risk assessment is rigorous and transparent, particularly in dealing with the uncertainty arising from the data available and their assessment and extrapolation to human populations. Hazard identification and characterization, i.e., a dose-response pattern, as applied to xenobiotics, are discussed first, and then the difficulties of applying this approach to nutrients are reviewed. Nutrients, in contrast to foreign chemicals, have specific and selective metabolic pathways and homeostasis, as well as specific functions. This is the source of differences in the nutrient risk assessments produced by various national and international advisory bodies. Although the same data are used in such exercises, different judgments are made about identifying adverse effects, the nature of uncertainties in the assessment, and in matching the upper levels with exposure assessments and dietary reference values. The establishment of different upper levels for different national and international communities is a source of confusion in public health policy and practice and a barrier to trade. It is proposed that a basis for harmonizing the existing approaches used in nutrient risk assessment would be the collaborative development of the model for establishing upper levels of intake for nutrients and related substances that has been recently described by a Joint Task Force of the World Health Organization and the Food and Agriculture Organization.