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.
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.
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.
