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: 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. |