[Food supplements--possibilities and limitations: Part 6, Safety and possible risks]

Due to the precautionary principle in consumer protection, thresholds for long-term safety of nutrients have to be defined. Three toxical indicators are of interest: lowest observed adverse effect level (LOAEL); no observed adverse effect level (NOAEL) und tolerable level of upper intake (UL). An uptake of a nutrient within the range of UL is without side effects even on the basis of long-term consumption. The UL can be used to derive maximum levels for nutrients in food supplements. In general, vitamins can be regarded as safe nutrients except for vitamin A. Adverse effects only occur at excessive intake far beyond the recommended daily allowances. In contrast, the range of safe intake for minerals, especially trace elements, is much smaller. This can be seen clearly in the case of selenium. In order to prevent severe selenium deficiency a plasma concentration of > 0.25 micromol/l (> 20 microg/l) must be reached. To minimize cancer risk a plasma concentration of 1.5 micromol/l (120 microg/l) is needed. First signs of selenium intoxications occur at plasma levels over 250 microg/l. It is the dose that makes the preventive effect and the poison as well.