Assessment of Zinc Intake in Relation to Tolerable Upper Intake Levels

Abstract

The Norwegian Food Safety Authority (NFSA, Mattilsynet) has requested the Norwegian Scientific Committee for Food Safety (VKM) to assess the intake of iron zinc in the Norwegian population in relation to tolerable upper intake levels (ULs). The existing maximum limit for zinc in food supplements is 25 mg/day.   VKM has also conducted scenario calculations to illustrate the consequences of amending the maximum limit to 1, 2, 5, 10, 15 or 20 mg/day.   Zinc is an essential trace element required for RNA, DNA and protein synthesis, cellular division, differentiation and growth (Mac Donald, 2000). Zinc is required for catalytic function in several enzymes and participates in all major biochemical pathways in the body. The function of the immune system depends on the ability of its cells to proliferate and differentiate, which is impaired in individuals with suboptimal zinc status (Barton et al. 2000). Due to its role in cell division and differentiation, adequate zinc nutrition is particularly important in children, and the requirements per kg body weight are highest in early life. The endogenous intestinal losses can vary from 7 mmol/day (0.5 mg/day) to more than 45 mmol/day (3 mg/day), depending on zinc intake (King and Turnlund, 1989).   The requirements for zinc vary according to age and bioavailability. Several bioactive compounds in food such as tannins and phytic acids interact with zinc absorption and increase zinc requirements. The requirements vary twenty-fold according to life stage and diet.    Zinc supplements, even at or slightly above the recommended intakes, can cause nausea and vomiting. The main concern with chronic zinc excess is, however, copper deficiency which is associated with several chronical illnesses. However, copper deficiency is uncommon due to the ubiquitous presence of copper in the diet.   VKM proposes to use the ULs set by IOM (2001) as they provide values also for children and adolescents. The tolerable upper intake level set for adults is 40 mg zinc per day from food (and water) and supplements.   Based on the scenario estimations, a dietary zinc intake at the 95th percentile and additionally 20 mg zinc from food supplements will lead to an intake close to the tolerable upper intake level established by IOM for adults. For adolescents and child populations the maximum amounts are 15 and 5 mg for 13- and 9-year-olds, respectively. For 2 and 4-yearolds, P95 from intake of zinc from food alone exceeds the UL.