food significantly decreased absorption. The absorption of dietary nickel is typically less than 10 percent.
Nickel is transported in blood bound primarily to albumin (Tabata and Sarkar, 1992). Although most tissues and organs do not significantly accumulate nickel, in humans the thyroid and adrenal glands have relatively high nickel concentrations (132 to 141 μg/kg dry weight) (Rezuke et al., 1987). Most organs contain less than 50 μg of nickel/kg dry weight.
Because of the poor absorption of nickel, the majority of ingested nickel is excreted in the feces. The majority of absorbed nickel is excreted in the urine with minor amounts excreted in sweat and bile.
Nickel may serve as a cofactor or structural component of certain metalloenzymes and facilitate iron absorption or metabolism in microorganisms. No studies to determine the biological role of nickel in higher animals or humans have been reported. Therefore, neither an Estimated Average Requirement, Recommended Dietary Allowance, nor Adequate Intake was established for nickel.
Major contributors to nickel intake are mixed dishes and soups (19 to 30 percent), grains and grain products (12 to 30 percent), vegetables (10 to 24 percent), legumes (3 to 16 percent), and desserts (4 to 18 percent) (Pennington and Jones, 1987). In food commodity groups, nickel concentrations are highest in nuts and legumes (128 and 55 μg/100 g, respectively), followed by sweeteners, including chocolate milk powder and chocolate candy. Of 234 foods analyzed, 66 percent had nickel concentrations less than 10 μg/100 g and 91 percent had concentrations less than 40 μg/100 g. Seven of these foods contained greater than 100 μg/100 g including nuts, legumes, and items with chocolate (Pennington and Jones, 1987). Major contributors of nickel to the Canadian diet include meat and poultry (37 percent), bakery goods and cereals (19 percent), soups (15 percent), and vegetables (11 percent) (Dabeka and McKenzie, 1995). Nielsen and Flyvholm (1983) suggested that nickel intakes in Denmark could reach over 900 μg/day by the consumption of certain foods based on the nickel composition and level of consump-