Manganese: Potential Health Benefits and Risks
Manganese is an essential trace mineral that is needed in the body to activate enzymes which help create cartilage and collagen to form strong bones and connective tissue. Furthermore, this trace mineral is a co-factor for an enzyme known as manganese superoxide dismutase, a potent antioxidant that helps fight free radicals in the body. It is also a co-factor for multiple other enzymes that assist in the metabolism of amino acids, carbohydrates and fats, regulate blood sugar levels, ensure proper functioning of the thyroid gland and help with the production of sex hormones. In addition, manganese is involved in the process of absorbing calcium and certain vitamins, assists in detoxification and wound healing and is required for proper functioning of the brain and nerves.
There are only about 12-20mg of manganese in the human body, found in the kidneys, liver, pancreas, adrenal glands and bones. Some people, especially vegetarians, may consume as much manganese in a single day. However, manganese is not absorbed easily and only about 15-25% of the ingested volume finds its way into the body’s organs. There are no official recommended dietary allowances for manganese. However, most experts agree that the adequate daily intake of manganese for adults is around 1.8mg for women and 2.3mg for men. Pregnant women should get 2.0mg and lactating women 2.6mg of manganese per day. The tolerable upper intake level for adults is estimated at 11mg of manganese per day.
Most experts believe that manganese deficiency is rare. Typical western diets contain between 2-7mg of manganese per day, which is well above the estimated adequate daily intake of 1.8mg and 2.3mg for adult women and men, respectively. Vegetarians may even ingest as much as 10mg of manganese per day. However, certain gastrointestinal conditions can impair the body’s ability to absorb manganese. In addition, manganese competes with certain other minerals for absorption. Research indicates that people who consume diets high in iron, calcium, phosphorus and magnesium may not be able to properly absorb and use manganese.
A deficiency of manganese may cause skin problems, infertility in women, reduced glucose tolerance, pancreatic damage, impaired vision and cognitive and bevavioral deficits in children, increased susceptibility to seizures, and bone demineralization and remodelling leading to skeletal abnormalities, osteoporosis and impaired growth.
Manganese toxicity, though not well explored, appears to be a bigger concern than deficiency. For those who consume high-manganese foods it is not impossible to exceed the daily tolerable upper intake level but dietary manganese rarely causes overdose. However, people should be careful when taking supplements. Also, those who have been fed intravenously for a long time are at an increased risk of manganese overdose. In addition, iron deficiency has been shown to increase the absorption of dietary manganese. Manganese is particularly toxic when inhaled because its dust is transported directly to the brain.
Symptoms of manganese overdose develop slowly over a period of several months. First, they include loss of appetite, insomnia, headaches, irritability, aggressive behavior and, sometimes, hallucinations. Later, patients may develop neurological problems that resemble those of Parkinson’s disease such as muscle stiffness and cramps, tremors and difficulty walking. People with liver damage are particularly susceptible to manganese toxicity. In addition, occupational inhalation of manganese dust may cause inflammatory lung problems.
Dietary Sources of Manganese
Plant foods are the best dietary sources of manganese. These include whole grain cereals (oats, rice, barley, quinoa, whole wheat, buckwheat, bulgur wheat, corn), green leafy vegetables and other vegetables (squash, beets, sea vegetables, tomatoes, carrots, cucumbers, bell peppers), spices (cloves, black pepper, cinnamon, oregano, peppermint, chilli peppers, thyme), berries (raspberries, strawberries, blueberries, cranberries), soy products, seeds (pumpkin, sesame, flaxseeds, sunflower), nuts (walnuts, peanuts, cashews, almonds, coconuts, hazelnuts), potatoes (sweet, regular), legumes (beans, lentils, peas), mushrooms, fruits (pineapple, banana, kiwifruit, grapes, figs), onions, garlic and molasses. An actual content of manganese in food typically depends on the soil in which the food was grown.
Supplements containing manganese are mainly used to treat manganese deficiency. In some cases, a physician may prescribe manganese to help treat other conditions including anemia, epilepsy, premenstrual syndrome, certain nervous disorders, diabetes, hypothyroidism, osteoporosis and osteoarthritis. However, the use of manganese supplements in the treatment of these conditions is rather new and needs more research. Therefore, not all experts support it. Excess manganese from supplements may interact with certain antibiotics (e.g., quinolone or tetracycline antibiotics), magnesium-containing antacids and laxatives and reserpine (an indole alkaloid used to control blood pressure). In addition, excess intake of manganese may also interfere with the absorption of iron and copper, leading to deficiency of these minerals.