Manganese
Characteristics: Manganese is an essential trace element that occurs naturally in many foods and is also available as a dietary supplement. Manganese is a cofactor for many enzymes, including superoxide dismutase, arginase, and pyruvate carboxylase. Through the action of these enzymes, manganese participates in the metabolism of amino acids, cholesterol, glucose and carbohydrates, the uptake of reactive oxygen species, bone formation, reproduction, and the immune response. Manganese also plays a role in blood clotting and hemostasis.

Absorption: Manganese is absorbed in the small intestine via an active transport system and possibly by diffusion at high intakes. After absorption, some manganese remains free, but most is bound to transferrin, albumin, and plasma alpha-2-macroglobulin. Manganese is taken up by the liver and other tissues. The human body contains about 10‒20 mg of manganese, of which 25 to 40% is in the bones. The liver, pancreas, kidneys, and brain also contain manganese. The body maintains stable tissue manganese concentrations by regulatory control of manganese absorption and excretion. More than 90% of the absorbed manganese is excreted in the bile into the stool, and a small amount is reabsorbed. Very little is excreted in the urine. Humans absorb only about 1 to 5% of manganese from food. In addition, manganese absorption efficiency increases with low manganese intake and decreases with higher manganese intake. Dietary iron intake and the amount of iron in the body appear to be inversely related to manganese absorption. Men absorb dietary manganese less efficiently than women, possibly because they typically have higher levels of iron in their bodies. Infants and children absorb a higher proportion of manganese than adults.

Dietary Supplements: In dietary supplements, manganese is present in many different forms, including amino acid chelates (e.g., manganese bisglycinate, manganese glycinate, and manganese aspartate). Other forms include manganese gluconate, manganese picolinate, manganese sulfate, manganese citrate, and manganese chloride. No data is available on the relative bioavailability of different forms of supplemental manganese. Multivitamin/mineral supplements usually contain 1.0‒4.5 mg of manganese. Supplements containing only manganese or manganese with several other nutrients are also available, and most contain 5‒20 mg of manganese.

Natural Sources: Manganese is present in a variety of foods, including grains, clams, oysters, clams, nuts, soybeans, legumes, rice, leafy greens, coffee, tea, and many spices such as black pepper. Drinking water also contains small amounts of manganese in concentrations of 1 to 100 µg/l.

Effect: Manganese supplementation can increase bone mineral density and bone formation, and further improve glucose tolerance, reduce oxidative stress, and improve endothelial dysfunction in diabetes.

Deficiency: Manganese deficiency is very rare in humans and its symptoms have not been firmly established. Very limited evidence in humans suggests that manganese deficiency can cause bone demineralization and poor growth in children, skin rashes, hair depigmentation, mood swings and increased premenstrual pain in women. Manganese deficiency can also alter lipid and carbohydrate metabolism and cause abnormal glucose tolerance.

Recommended daily dose: adult: 2.3 mg for men, 1.8 mg for women (2.0 mg during pregnancy, 2.6 mg during breastfeeding).

Side effects: Manganese is probably safe for adults 19 years of age and older when consumed in amounts up to 11 mg per day.

Interaction: Not documented.

Pregnancy: Safe in usual doses.

Breastfeeding: Safe in usual doses.

Toxicity: High dietary intake of manganese is not dangerous. However, manganese toxicity has occurred in people working in occupations such as welding and mining who were exposed to high amounts of manganese from chronic inhalation of manganese dust. Manganese intoxication mainly affects the central nervous system and can cause tremors, muscle spasms, tinnitus (ringing in the ears), hearing loss and unsteadiness in the legs. Other symptoms include mania, insomnia, depression, delusions, anorexia, headaches, irritability, leg weakness, changes in mood and short-term memory, altered reaction times, and decreased hand-eye coordination. These symptoms can progress to neuromotor disturbances like those associated with Parkinson's disease, including changes in gait and balance, tremors, and stiffness. Iron deficiency increases the absorption of manganese and therefore can worsen the symptoms of manganese toxicity. People with chronic liver disease have impaired biliary elimination of manganese and are more susceptible to manganese neurotoxicity and other adverse effects of excessive manganese intake.