Risk assessment of micronutrients.

Risk assessment of micronutrients has to take into account two different intake-response relationships; the risk of deficiency, which decreases with increase in intake, and the risk of toxicity, which increases with increase in intake. The available databases on micronutrients tend to focus on benefits at low intakes, and there are usually few reliable data on hazard identification and characterisation at high intakes. Application of the usual default uncertainty factors for species differences, human variability and database inadequacy could result in "recommended" upper intake levels that would cause deficiency. There have been a number of comprehensive reviews that have used low, and largely arbitrary, uncertainty factors to establish tolerable upper intake levels for vitamins and minerals. A recent FAO/WHO Workshop developed a structured approach to the application of a single composite uncertainty factor. Risk-benefit approaches have been developed recently that balance the risk of toxicity against the risk of deficiency, and offer the potential for more scientifically based methods.