Manganese (Mn) is an essential trace mineral that is concentrated
primarily in the bone, liver, pancreas, and brain. This mineral is a
component of several enzymes: (1) Mn-superoxide dismutase which prevents
tissue damage due to lipid (fat) oxidation; (2) pyruvate carboxylase
which helps break down carbohydrates; and (3) arginase which is
important for nitric oxide synthesis and the formation of urea in the
urine. Manganese also activates numerous enzymes, particularly
glycosyltransferases which are involved with the formation of cartilage
in bone and skin.
IMPORTANCE: Manganese plays important roles in many bodily functions as a part of several enzymes. Among its many uses, Manganese is helpful in blood-clotting, bone mineralization, and possibly as an anti-oxidant. Deficiencies of this mineral have been associated with depressed growth of hair and nails, scaly dermatitis, weight loss, and impaired blood clotting. Some preliminary research suggests that supplementing with Manganese may help relieve the symptoms of osteoporosis, osteoarthritis, and PMS. An antioxidant nutrient; important in the blood breakdown of amino acids and the production of energy; necessary for the metabolism of Vitamin B-1 & Vitamin E; Activates various enzymes which are important for proper digestion & utilization of foods; is a catalyst in the breakdown of fats & cholesterol; helps nourish the nerves and brain; necessary for normal skeletal development; maintains sex hormone production.
Deficiencies: In animals manganese deficiencies produce abnormalities in brain function, glucose tolerance, reproduction, and skeletal and cartilage formation. In humans, gross deficiencies have not been documented in free-living populations but deficiencies created in a metabolic unit suggest the mineral is important to maintain the integrity of the skin, bone and menstrual cycle, and in cholesterol metabolism. Certain population groups have been reported to have suboptimal status, including children with birth defects or on long-term total parenteral nutrition and patients with Perthes' disease, hip dislocations in Down's syndrome, osteoporosis, multiple sclerosis, non-trauma epilepsy, senile cataracts, acromegaly, and amyotrophic lateral sclerosis. May result in paralysis, convulsions, dizziness, ataxia, loss of hearing, digestive problems, blindness and deafness in infants.
Diet recommendations: The Estimated Safe and Adequate Dietary Intakes (ESADDIs) for Mn each day are 2.0-5.0 mg for adults. For children, ESADDIs are 1.0-1.5 mg for ages 1-3 yrs; 1.5- 2.0 mg for ages 4-6 yrs, 2.0-3.0 mg for ages 7-10 yrs, and 2.0-5.0 for ages 11-14 yrs. Recent research suggest that recommendations for formula-fed infants are 0.005 mg/day and 0.030 mg/day for breast-fed infants.
Usual dietary intakes in the U.S. are about 2.2 and 2.8 mg/day for adult women and men, respectively. However, much higher intakes (10-18 mg) are found with vegetarian diets and those based on whole-grain products. Thus, the current ESADDI may be too conservative for adults.
Food sources: Excellent sources of manganese (>1 mg/serving) include pecans, peanuts, pineapple fruit and juice, oatmeal, shredded wheat and raisin bran cereal. Good sources (> 0.5 mg/serving) are beans (pinto, lima, navy), rice, spinach, sweet potato, and whole wheat bread. Very little Mn is found in meat, poultry, fish, milk, dairy products or sugary and refined foods.
Dietary components that may adversely affect manganese absorption, retention or excretion include iron, phosphorus, phytates, fiber, calcium, copper, and polyphenolic compounds.
Toxicity: Toxicity has occurred from industrial exposure, such as miners breathing manganese dust and drinking contaminated well water. Symptoms of toxicity are the development of a schizophrenia with nervous disorders resembling Parkinson's disease. The reference dose (RfD) set by the EPA in 1993 is 10 mg/day for a 70 kg body weight; this dietary level is considered to be without significant risk of a deleterious effect for a lifetime of exposure. There is no evidence of toxicity occurring from ingestion of typical diets. For drinking water, the RfD is 0.2 mg Mn/L.
Recent research: Lower manganese bloods levels have been observed in patients with osteoporosis, non-trauma epilepsy and Perthes' disease. Low dietary levels of manganese that lower the levels of Mn-superoxide dismutase may increase colon cancer susceptibility. Magnetic resonance imaging (MRI) is a very sensitive technique that can detect toxic accumulation of Mn in the brain.