MANGANESE

Function and Essentiality Manganese (Mn) is a component of enzymes such as pyruvate carboxylase, mitochondrial superoxide dismutase and arginase, and it also activates many other enzymes eg hydrolases, glycosyl transferases, kinases, prolinase and phosphotransferases (1). The body contains 12-20 mg (0.2-0.4 mmol*) of Mn, most of which is intracellular. About 25 per cent of this is in the skeleton and is relatively immobile. Highest concentrations are found in the pancreas and liver. Absorption occurs throughout the length of the small intestine but the efficiency is reportedly low, and there is as yet no evidence on how it alters with Mn deprivation or excess. Systemic Mn homeostatis is achieved principally through hepato-biliary and intestinal secretion. Studies in animal models, and preliminary studies in human infants, suggest that in the early postnatal period intestinal uptake and whole body retention is increased. This appears to be a consequence of an efficient intestinal uptake and transfer of the element and reduced hepato-biliary secretion (2).


Requirements Human Mn deficiency has not been observed other than in two experimental studies only one of which was part of a systematic study of Mn metabolism. It would seem therefore that current population intakes are adequate (3). Recourse to this pragmatic approach of determining DRVs is further enforced because the lack of adequate data on body composition data and of detailed'studies of turnover and metabolism. The Panel therefore set no RNIs but safe intakes are believed to lie above 1.4 mg (26 µmol)/d for adults and above 16 µg (0.3 µmol)/kg/d for infants and children.


Intakes Total Mn intakes in Britain were estimated at 4.6 mg (84 µmol)/person/d of which half was derived from tea (4). Observed mean dietary Mn intakes in the UK include 5.5 mg and 3.3 mg/d in pregnant and non-pregnant women (5) and 60 µg/kg/d in children aged 3 months to 8 years (6). The calculated total Mn output in human breast milk during the first three months postpartum is 1.9 µg/d and 1.6 µg/d in the ensuing three monthS (7). Healthy term infants fed a formula based on cow's milk had intakes of 28-42, 16-24 and 18-32 µg/kg/d at 1, 2 and 3 months of age with respective mean maximum retentions of 7.7, 6.1 and 8.0 µg (8). Older infants on mixed weaning diets have intakes of 71 µg (1.3 µmol)/kg/d and 8 µg (0.2 µmol)/kg/d at 6 and 12 months (9).


Guidance on high intakes Manganese is one of the least toxic of all elements because when excess is consumed absorption is very low and that which is absorbed is efficiently excreted via the bile and kidneys (10). Toxic reactions in man have only been reported in miners exposed to Mn ores, but these were attributed to continuous absorption from dust in the lungs rather than from the intestine (11, 12).

*1 mmol=55 mg


References

1 Keen C L, Lonnerdal B, Hurley L S. Manganese. In: Frieden E, ed. Biochemistry of the Essential Ultratrace Elements. New York: Plenum Press, 1984; 89-132.

2 Kies C. Nutritional Bioavailability of Manganese. Washington DC: American Chemical Society, 1987.

3 Anonymous. Manganese deficiency in humans: fact or fiction. Nutr Rev 1988; 46: 348-352.

4 Wenlock R W, Buss D H, Dixon E J. Trace nutrients 2. Manganese in British foods. Br J Nutr 1979; 41: 253-261.

5 Armstrong J. Trace Element Metabolism in Human Pregnancy. M. Phil. Thesis. Aberdeen: Robert Gordon's Institute of Technology, 1985.

6 Alexander F W, Clayton B E, Delves H T. Mineral and trace metal balances in children receiving normal and synthetic diets. Quart JMed 1974; 43: 89-11 1.

7 Casey C E, Neville M C, Hambidge K M. Studies in human lactation: secretion of zinc, copper and manganese in human milk. Am J Clin Nutr 1989; 49: 773-785.

8 Miller C. A study of the Influences on Mineral Homeostatis in Infants fed synthetic Milk Formulae Ph.D. Thesis. Aberdeen: Robert Gordons Institute of Technology, 1987.

9 Gibson R S, DeWolfe M S. The dietary trace metal intake of some Canadian full-term and low birthweight infants during the first twelve months of infancy. J Can Diet Assoc 1980; 41: 206-215.

10 Underwood E J. Trace elements in Human and A nimal Nutrition. 4th ed. New York: Academic Press, 1977; 170-181.

11 Borg D C, Cotzias G C. Incorporation of manganese into erythrocytes as evidence for a manganese porphyrin in man. Nature 1958; 182: 1677-1678.

12 Cotzias G C. Manganese and heart disease. Physiot Rev 1958; 38: 503-532.