Manganese, a trace mineral that participates in many enzyme systems in the body, was first considered an essential nutrient in 1931. Researchers discovered that experimental animals fed a diet deficient in manganese demonstrated poor growth and impaired reproduction. Manganese is found widely in nature, but occurs only in trace amounts in human tissues. The human body contains a total of 15-20 milligrams of manganese, most of which is located in the bones, with the remainder found in the kidneys, liver, pancreas, pituitary glands, and adrenal glands.

Manganese is a very common compound that can be found everywhere on earth. Manganese is one out of three toxic essential trace elements, which means that it is not only necessary for humans to survive, but it is also toxic when too high concentrations are present in a human body. When people do not live up to the recommended daily allowances their health will decrease. But when the uptake is too high health problems will also occur. In the human body, manganese functions as an enzyme activator and as a component of metalloenzymes (an enzyme that contains a metal ion in its structure).

Manganese activates the enzymes responsible for the utilization of several key nutrients including biotin, thiamin, ascorbic acid, and choline. It is a catalyst in the synthesis of fatty acids and cholesterol, facilitates protein and carbohydrate metabolism, and may also participate in the production of sex hormones and maintaining reproductive health.

In addition, manganese activates the enzymes known as glycolsyltranserferases and xylosyltransferases, which are important in the formation of bone. It has also been theorized that manganese is involved in the production of the thyroid hormone known as thyroxine and in maintaining the health of nerve tissue.

The uptake of manganese by humans mainly takes place through food, such as spinach, tea and herbs. The foodstuffs that contain the highest concentrations are grains and rice, soya beans, eggs, nuts, olive oil, green beans and oysters. After absorption in the human body manganese will be transported through the blood to the liver, the kidneys, the pancreas and the endocrine glands.

Manganese effects occur mainly in the respiratory tract and in the brains. Symptoms of manganese poisoning are hallucinations, forgetfulness and nerve damage. Manganese can also cause Parkinson, lung embolism and bronchitis. When men are exposed to manganese for a longer period of time they may become impotent. A syndrome that is caused by manganese has symptoms such as schizophrenia, dullness, weak muscles, headaches and insomnia.

Because manganese plays a role in a variety of enzyme systems, dietary deficiency of manganese can impact many physiological processes. In experimental animals, manganese deficiency causes impaired growth, skeletal abnormalities, and defects in carbohydrate and fat metabolism. In addition, offspring of experimental animals fed manganese-deficient diets develop ataxia, a movement disorder characterized by lack of muscle coordination and balance. This condition is caused by poor development of the otoliths, the structures in the inner ear that are responsible for equilibrium.

In humans, manganese deficiency is associated with nausea, vomiting, poor glucose tolerance (high blood sugar levels), skin rash, loss of hair color, excessive bone loss, low cholesterol levels, dizziness, hearing loss, and compromised function of the reproductive system. Severe manganese deficiency in infants can cause paralysis, convulsions, blindness, and deafness. It is important to emphasize, however, that manganese deficiency is very rare in humans, and does not usually develop unless manganese is deliberately eliminated from the diet. In addition, it has been suggested that magnesium substitutes for manganese in certain enzyme systems if manganese is deficient, thereby allowing the body to function normally despite the deficiency.

In 2000, the Institute of Medicine at the National Academy of Sciences established the following Tolerable Upper Intake Levels (UL) for manganese:

• Infants: not established (no supplemental manganese should be given)
• 1-3 years: 2 milligrams
• 4-8 years: 3 milligrams
• 9-13 years: 6 milligrams
• 14-18 years, including pregnant and lactating women: 9 milligrams
• Greater than 19 years, including pregnant and lactating women: 11 milligrams

Significant amounts of manganese can be lost in food processing, especially in the milling of whole grains to produce flour, and in the cooking of beans. Three and one half ounces of raw navy beans, for example, start out with about 1 milligram of manganese. This amount drops by 60% to 0.4 milligrams after cooking.