THE BIOLOGICAL IMPORTANCE OF NICKEL IN THE FOOD-CHAIN

The ultra trace element nickel (Ni) is both essential and toxic for animals and humans. A Ni-poor nutrition of < 0.1 mg/kg dry matter led to Ni deficiency symptoms. Ni is a component of the urease and it is also essential for several species of bacteria which occur in the rumen of ruminants. Ni deficiency symptoms, however, have not yet been found in animals and humans since the Ni offer exceeds the Ni requirement. On the other hand, an external Ni exposure to nickel alloys induces Ni dermatitis in 8 to 14% of nickel-sensitive women and in > 1% of men after the filling of the Ni depot in the body. Experiments with 4 animal species showed that Ni exposure leads to disturbances in the Mg and above all in the Zn metabolism. Ni excess induces Zn deficiency symptoms which are similar to parakeratosis in pigs. They correspond to the symptoms of nickel allergy in humans. Therefore, the Ni intake of humans, which leads to the gradual filling of the Ni pool in the body and which can then induce nickel dermatitis in Ni-sensitive women and men, is of particular importance. The Ni requirement of adults does not exceed 25 to 35 mu g/day. The Ni balance of men and women was positive (+ 20%) and shows the Ni incorporation even in the case of a Ni consumption which exceeds by far the requirement.