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Manganese (Mn) is a mineral necessary in very tiny (trace) amounts for human health. In large quantities, manganese is poisonous. Manganese is used in some enzyme reactions and for the proper development of bones and cartilage. Humans must meet their needs for manganese from their diet. Manganese is
(Illustration by GGS Information Services/Thomson Gale.)
found mainly in plants and in small quantities in some drinking water.
Researchers understand less about how manganese functions in the body than they do about many other minerals. Studies have shown that manganese is necessary for proper development of healthy bones and cartilage in animals. It is highly likely that manganese plays the same role in the development of human bones and connective tissue, although manganese deficiency is so rare in humans (and putting people on a prolonged manganese-free diet would be an unethical experiment) that this has not been proven experimentally.
Manganese is acquired through diet. It is not evenly distributed in the body but is concentrated in the bones, liver, pancreas, and brain. Excess manganese is removed in bile, a digestive fluid made by the liver. The role of manganese in health is not well understood. Both manganese deficiency and manganese excess are rare. The few cases of dietary manganese excess that have been recorded have resulted from accidental exposure such as from drinking water contaminated with manganese-containing industrial waste. The United States Environmental Protection Agency (EPA) recommends a concentration of manganese no higher than .05 mg/L in drinking water. Side effects of high levels of manganese include loss of appetite, headaches, tremors, convulsions, and mental changes such a hallucinations. If manganese is inhaled in dust or vapor, it can cause severe damage to the nervous system. Some miners and industrial workers are at risk of being exposed to airborne manganese.
Normal manganese requirements
The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for many vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determinean RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.
The IOM has not set RDAs for manganese because not enough information is available about the need for manganese in humans. Instead, it has set AI levels for all age groups. Because high levels of manganese affect the nervous system, the ULs are very conservative. Some experts point out that vegans and vegetarians who eat large quantities of whole grains routinely take in manganese in amounts well above the established UL without any obvious adverse effects. IAs and ULs for manganese are measured in milligrams (mg).
The following list gives the daily IAs and ULs for manganese for healthy individuals as established by the IOM.
Sources of manganese
Almost all people get enough manganese from their normal diet. Good sources of manganese include nuts, seeds, whole grains, leafy green vegetables, and tea. Some water that is high in minerals (“hard” water) may contain small amounts of manganese; the amount varies depending on location. Whole grains contain manganese, but processing removes most of it. Therefore brown rice is a good source of manganese, but white rice is not. Whole wheat flour has more manganese than white flour, and wheat bran has more than either type of flour. Manganese is also found in multi-vitamin/mineral supplements, and in single-ingredient supplements. Joint supplements that contain glucosamine and chrondroitin may also contain manganese. The best way to get an adequate amount of manganese
is to eat a healthy diet high in green vegetables and whole grains.
The following list gives the approximate manganese content for some common foods:
Controversial health claims for manganese
Manganese supplements have not been proven effective in treating or preventing any specific disease or condition. However, based on a small number of laboratory and animal studies, practitioners of alternative medicine sometimes recommend supplemental manganese for the following conditions. These uses are considered speculative by practitioners of conventional medicine.
Liver damage may reduce the rate at which magnesium is removed from the body. People with liver damage (e.g. cirrhosis) may be at higher risk of developing symptoms of manganese excess.
Antacids and laxatives that contain magnesium (e.g. milk of magnesia) may reduce the amount of manganese absorbed from food.
No complications are expected from manganese acquired through food and water. Individuals who take multivitamin/mineral supplements containing manganese are unlikely to have any adverse effects. People who take manganese or joint supplements should be alert to how much manganese they are consuming, although overdose is extremely rare.
Parents should have few concerns about children getting either too much or too little manganese. Supplemental manganese should rarely be necessary. Parents should encourage their children to eat a diet high in fruits, vegetables, and whole grains.
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Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892-7517 Telephone: (301)435-2920. Fax: (301)480-1845. Website: <http://dietary-supplements.info.nih.gov>
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Helen M. Davidson