Nickel is a trace element, required in minute quantities by the human body. It is found widely in the environment and also in almost all tissues in the human body. Though present in minute quantities, nickel can accumulate in the kidneys, bones and thyroid gland and cause toxicity.
The functions of nickel in the human body are still not very clear. Enzymes containing nickel have not been found, though nickel functions to activate or inhibit enzymes containing other elements. Apart from the role in enzymes, nickel is also involved in the production and action of some hormones.
The possible health benefits of nickel include optimal growth, healthy skin and bone structure. It may also be involved in iron metabolism, as it influences iron absorption from foods and may also play a role in production of red blood cells. It is required for metabolism of glucose, lipids, hormones and cell membrane.
Plants are the main dietary source of nickel. Plants grown in soil contaminated with nickel will have a higher content of nickel in them. Some rich sources of this mineral are peas, dried beans, chocolate, nuts and oats. Animal foods are a poor source of nickel, while drinking water contributes to nickel considerably.
There is not enough data to establish dietary recommendations for nickel. Also, nickel content of different foodstuffs is very varied which further makes it difficult to set recommendations. Daily dietary intakes for nickel are estimated to be 100 micrograms. This amount can be met by the typical diet, consisting of food from various food groups on a daily basis.
Nickel deficiency is rare in humans as nickel requirements are low and availability high from dietary sources. A condition of nickel deficiency has not been clearly defined in humans, though it has been demonstrated in animals. Nickel deficiency in these cases has been shown to affect a number of functions. The symptoms observed in animal studies include depressed growth, reproductive changes and altered lipid and glucose levels in the blood.
Other changes observed in a nickel deficient state include, changes in skin color, coarse hair, hormone imbalance and abnormal bone growth. Liver function is impaired and iron metabolism is affected, resulting in poor absorption of iron. Metabolism of some other nutrients like calcium and vitamin B12 is also altered due to nickel deficiency.
Dietary excess of nickel is not common, though toxicity symptoms have been observed with nickel contact and inhalation of nickel fumes. Some people are believed to be nickel sensitive. Nickel contact with the skin in such people, as seen with jewelry containing nickel, can cause skin rash and a kind of dermatitis called ‘nickel itch’. This starts with symptoms of itching and proceeds to ulceration.
Nickel is considered carcinogenic in large quantities. Large intakes can increase the risk of cancers of the lung, nose and larynx. Respiratory problems including asthma and bronchitis have been attributed to nickel toxicity. Bone development, resistance to infection and shortness of breath, dizziness and altered immune function are some of the other problems associated with nickel excess.