Absorption of manganese

To determine the effects of the deprivation of specific micronutrients on the water hyacinth (Eichhornia crassipes), Colley et al. (1979) studied the rate of uptake of iron and manganese in comparison with phosphorus. Results indicated that all three elements were actively absorbed by the root systems, but the rates of absorption differed markedly. The rate of absorption of manganese by roots was 13 and 21 times that for radio-iron and -phosphorus, and iron was taken up by the roots at nearly twice the rate of phosphorus. Manganese translocation appeared to be faster than phosphorus translocation by an order of magnitude and 65 times faster than iron translocation. 

Manganese is an essential nutrient for humans with a daily estimated adequate safe and daily dietary intake of 2.5 to 5.0 mg (1). Yet trace mineral nutriture depends not only upon dietary intake, but also upon availability for absorption. Currently, little is known regarding the influence of dietary factors on the absorption of manganese. Thus the intent of these studies was to (a) develop a test that would readily measure Mn bioavailability in humans and (b) utilize this test to determine the influences of various dietary factors on Mn bioavailability. 

Since almost nothing is known about the effect of isolated fibers on the absorption of manganese and constituents of dietary fiber vary both in chemical and physical properties, the effects of two major types of fiber — cellulose and pectin — were examined using our protocol. The effect of phytate was also measured since it is associated with high fiber foods and has been reported to increase requirements for manganese (40). 

Although little is known about the effects of pectins on the absorption of manganese, administration of pectin has been shown to increase the excretion of bile acids in humans (48). In the only previous study related to the influence of pectin on manganese metabolism, fuccidan—a polyuronic acid of seaweed origin—was found to reduce the uptake of manganese in tied-off segments of rat jejunum by up to 77% (51). 

Wheat bran and whole wheat cereals quantitatively contain high amounts of manganese and are often listed as particularly valuable sources of manganese. However, zinc also is contained in appreciable amounts in wheat bran and whole wheat products but is poorly absorbed by the human from these sources. This has been attributed to either the phytate or the fiber contents of these products or a combination of these two dietary factors. These same factors may also affect the absorption of manganese. 

Manganese exists in several different valence states but is thought to be absorbed in the reduced state (+2) as is iron. Hence, addition of ascorbic acid might be expected to enhance the apparent absorption of manganese. 

Calcium has long been implicated as a dietary factor which inhibits the absorption of manganese. Since manganese is better absorbed in the oxidized (+2) than in the reduced state (+3 or +4), any factor which increases gastrointestinal tract pH (increases alkalinity) would be expected to inhibit manganese utilization. Calcium carbonate, a commonly used antacid by humans as well as a calcium nutrient supplement, has been found to have a greater adverse effect on apparent manganese absorption in humans than does milk. 

Manganese in the human is also thought to be absorbed maximally in the duodenum in the II valence state. Therefore, as with manganese uptake by plants, the pH of the upper gastro-intestinal tract might be expected to be of importance in the absorption of manganese by the human. 

In conclusion, research results indicate that calcium apparently inhibits the absorption of manganese from the intestinal tract. Different sources of calcium apparently affect manganese to varying degrees. Whether or not this is due to changes in intestinal acidity/alkalinity, to possible competition between manganese and calcium for absorption sites, or to a combination of factors is unknown. 

Experiments in isolated segments of rat intestine (58) showed a reduction in net absorption of manganese from a 10 -M solution in the presence of a 10 -M solution of ascorbate. Dehydroascorbate had no effect on net manganese absorption, but it increased transfer of the manganese to the carcass. 

Two studies in suckling rat pups found differing absorptions of manganese from different milks and formulas. The first study (Lonnerdal et al. 1987) found that the percent of Mn (added to the food source as an extrinsic label) retained (measured as whole-body retention) in 14-day-old pups fed breast milk, cow milk, cow milk formula, and soy formula, was 82, 90, 77, and 65%, respectively. 

MMT. No studies were located regarding absorption of manganese following oral exposure to MMT in either humans or animals. The available studies (Hanzlik et al. 1980 Hinderer 1979 Hysell et al. 1974 Komura and Sakamoto 1992) indicate absorption is occurring because toxicity is observed following MMT exposure however, no absorption rates or relative amounts were provided in these studies. 

Maneb or mancozeb. No studies were located regarding absorption of manganese in humans following oral exposure to maneb or mancozeb. 

Recently, manganese levels in foods have been determined in order to define more clearly human dietary requirements or levels of absorption of manganese from the diet (Tinggi et al. 1997). Atomic absorption... 

Garcia-Aranda JA, Lifshitz F, Wapnir RA. 1984. Intestinal absorption of manganese in experimental malnutrition. J Pediatr Gastroenterol Nutr 3 602-607. 

Garcia-Aranda JA, Wapnir RA, Lifshitz F. 1983. In vivo intestinal absorption of manganese in the rat. J Nutr 113 2601-2607. 

INTERRELATIONSHIPS. Manganese interacts with other nutrients. Excess calcium and phosphorus interfere with the absorption of manganese the functions of manganese, copper, zinc, and iron may be interchangeable in certain enzyme systems and manganese and vitamin K work together in the promotion of blood clotting. 

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