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 may aid in blood-clotting, bone mineralization, and possibly as an anti-oxidant. Therefore, it may be important in the blood breakdown of amino acids and the production of energy; necessary for the metabolism of vitamin B1 & 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.