Nickel has been considered as a possibly essential trace mineral for several decades. We have a total of about 10 mg. in our body, but we still do not know exactly what it does. Most of the nutritional research on nickel has been done with chicks and rats. It is an essential nutrient for these animals, and they suffer considerable problems with nickel deficiency.
Nickel is found in many foods and in all animal tissues. While it is found in most human tissues, so far as we know, it is not concentrated in any particular tissues. Since it occurs in food and is part of the earth's crust and not a contaminant, many scientists feel that it is probably essential to humans. But nickel is potentially toxic in its gaseous form, nickel carbonyl.
Nickel is rather poorly absorbed from the gastrointestinal tract, probably at less than 10 percent. It is carried in the body attached to a protein, forming a molecule called nickeloplasmin. Most nickel is eliminated in feces, some in urine, and a bit in perspiration. The kidneys can either clear excess nickel or retain it; such a control mechanism suggests essentiality.
Sources: Nickel is contained in many foods. Most beans, soybeans, lentils, and split and green peas have fairly high amounts. Nuts, such as walnuts and hazelnuts, are the best sources of nickel. Of the grains, oats have the highest content, followed by buckwheat, barley, and corn. Many vegetables and some fruits, such as bananas and pears, have moderate amounts. Animal products and fatty foods are fairly low in nickel; of these, herring and oysters are the highest. Refined foods are also low. It is possible that the nickel in grains forms a phytate, reducing the amount of nickel available.
There are external, nonfood sources of nickel also, but it is not clear how much nickel we actually absorb from these sources. Nickel is found in coins, costume jewelry, eyeglass frames, hair clips, pins, scissors, and some kitchen appliances. Regular contact with these nickel products may allow some absorption into the body. Allergic dermatitis from nickel products is not at all uncommon.
Functions: The biological function of nickel is still somewhat unclear. Nickel is found in the body in highest concentrations in the nucleic acids, particularly RNA, and is thought to be somehow involved in protein structure or function. It may activate certain enzymes related to the breakdown or utilization of glucose. Nickel may aid in prolactin production, and thus be involved in human breast milk production.
Most of the information about nickel comes from testing with animals, and its relevancy to humans is still not proven. More research is needed to reveal the properties of this interesting mineral in the human body.
Uses: There are presently no clear uses for nickel supplementation. Studies have shown that there are increased levels of nickel in patients following heart attacks, burns, and strokes, and with toxemia of pregnancy. Whether this is a partial cause or, as is more likely, a result of tissue metabolism or represents some other function of nickel is not as yet known. Decreased levels of nickel have been seen in psoriasis, in cirrhosis of the liver, and with kidney disease, but it has not been shown that nickel treatment helps any of these conditions.
Deficiency and toxicity: Toxicity is the main concern here-not from elemental nickel or the nickel found in foods but from inhaled nickel carbonyl, a carcinogenic gas that results from the reaction of nickel with heated carbon monoxide, from cigarette smoke, car exhaust, and some industrial wastes. Nickel carbonyl is toxic and can cause symptoms such as frontal headaches, nausea, vomiting, or vertigo with acute exposure. Inhaled nickel accumulates in the lungs and has been associated with increased rates of lung, nasal, and laryngeal cancers. Nickel allergy can also cause local skin or systemic reactions. The nickel in jewelry, dental materials, or prosthetic joints or heart valves may also be allergenic sources.
Nickel deficiency has not been shown to be a concern in humans, but it is definitely a problem in chicks and other small animals, where low nickel can lead to decreased growth, dermatitis, pigment changes, decreased reproduction capacities, and compromised liver function. In humans, increased sweating, such as from exercise, can cause nickel losses, and extra dietary nickel may be required to maintain its still mysterious functions.
Requirements: There is, of course, no RDA for nickel. About 500 mcg. is probably a safe daily intake; the average dietary intake is about 200-750 mcg. If nickel is clearly found to be essential, the minimum requirement would likely be 50-100 mcg. Nickel is easily obtainable in most diets and is not usually contained in any supplements, except for occasional trace mineral formulas.