Third National Health and Nutrition Examination Survey and the Continuing Survey of Food Intakes by Individuals, were approximately 14 mg/day (Appendix Tables C-25 and D-4). The median intakes for women in the same age range were approximately 9 mg/day. These values are similar to those found for zinc intakes of Canadian adults (Appendix Table F-3).
In 1986, approximately 16 percent of Americans took supplements that contained zinc (Moss et al., 1989; see Table 2-2). The median total (food plus supplements) zinc intakes by adults taking supplements were similar to those of adults who did not take zinc supplements (Appendix Table C-26). Intake of zinc supplements, however, greatly increased the intakes in the upper quartile compared to those who did not take zinc supplements.
The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals. Although members of the general population should be advised not to routinely exceed the UL, intake above the UL may be appropriate for investigation within well-controlled clinical trials. Clinical trials of doses above the UL should not be discouraged, as long as subjects participating in these trials have signed informed consent documents regarding possible toxicity and as long as these trials employ appropriate safety monitoring of trial subjects. In addition, the UL is not meant to apply to individuals who are receiving zinc under medical supervision.
Although no evidence of adverse effects from intake of naturally occurring zinc in food was found, the UL derived here applies to total zinc intake from food, water, and supplements (including fortified food). Adverse effects associated with chronic intake of supplemental zinc include suppression of immune response, decrease in high-density lipoprotein (HDL) cholesterol, and reduced copper status.