Nickel is a natural element of the earth’s crust and is found in food, water, soil, and air. Surprisingly, food is the major source of nickel exposure, with an average intake for adults estimated to be approximately 100 to 300 µg/day (1), or 1.6 – 5.0 µg/kg body weight (bw)/day based on a 60 kg body weight. Major food sources of nickel include grains and grain products, vegetables, meat, poultry, nuts, legumes, sweeteners and chocolate (2). The Institute of Medicine’s (IOM’s) tolerable upper limit (UL) for adults is 1.0 mg/day (17 µg/kg bw/day) of soluble nickel salts, based on the no observable adverse effect level (NOAEL) for changes in body weights of rats in subchronic and chronic toxicity studies (5000 µg/kg bw/day) (2). Based on the IOM UL, current levels of exposure to dietary nickel in the United States are safe.
The European Food Safety Authority (EFSA) recently released an opinion on the risks to public health related to the presence of nickel in food and drinking water (3). EFSA utilized the benchmark dose at 10% extra risk (BMDL10) for post-implantation fetal loss from an unpublished two generation rat study conducted by Springborn Laboratories in 2000 (280 µg/kg bw/day) to develop a chronic tolerable daily intake (TDI) of 2.8 µg nickel/kg bw/day. This study was not available at the time the IOM established the UL of 1.0 mg/day. Recognizing that the most commonly reported adverse health effect associated with nickel exposure is contact dermatitis and dietary exposure to nickel can cause flare-ups in people with contact allergy to nickel, EFSA selected systemic contact dermatitis as the critical effect for the assessment of acute effects of nickel. A lowest BMDL10 of 1.1 µg nickel/kg bw was derived for the incidence of systemic contact dermatitis in humans following oral exposure to nickel. EFSA concluded that nickel-sensitized individuals could safely ingest 10 times less nickel on an acute basis than the BMDL10 of 1.1 µg nickel/kg bw (0.11 µg nickel/kg bw). The tolerable daily intakes developed by EFSA are considerably lower than the IOM’s UL of 17 µg/kg bw/day.
An exposure assessment conducted by EFSA showed that for the European population, the mean and 95th percentile chronic dietary exposure to nickel across all age classes ranged from 2.0 – 13.1 µg nickel/kg bw/day and 3.6 – 20.1 µg nickel/kg bw/day (respectively), higher than the TDI of 2.8 µg nickel/kg bw/day. Acute exposures were estimated to be 2.5 – 1.43 µg nickel/kg bw/day at the mean and 5.5 – 3.50 µg nickel/kg bw/day at the 95th percentile. Based on the results, the Panel concluded that the current dietary exposure to nickel is of concern for the general European population and for nickel-sensitized individuals that may develop eczematous flare-up skin reactions. The Panel expressed the need for mechanistic studies to assess the human relevance of the effects on reproduction and development in rats. As shown in the first paragraph of this article, nickel consumption by Americans is similar to that of Europeans. Therefore, Americans, as well as Europeans, may be at risk for developing toxicity from nickel at current dietary levels. Food producers should take note of the new study by EFSA and determine whether their ingredients could be significant dietary sources of nickel.
References
EPA (2000). Nickel Compounds – Hazard Summary. Available at http://www.epa.gov/airtoxics/hlthef/nickel.html.
Institute of Medicine (2001). Arsenic, boron, nickel, silicon and vanadium. In Dietary reference intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington, D.C. p. 82-161.
EFSA (2015). Scientific opinion on the risks to public health related to the presence of nickel in food and drinking water. EFSA Journal 13(2): 4002.