The conclusions in the opinion are limited to the use of manganous salts in foods for human consumption and do not concern the use of manganese in animal feeds.
The available information indicates that a wide margin exists between present intake levels of manganese as manganous salts and those levels that have been reported to produce harmful effects. Manganese is an essential nutrient that is required for the optimal functioning of several metabolic systems largely through its role as a prosthetic group or as essential cofactor. Divalent manganese is among the least toxic of the trace elements. As was indicated in the review of the experiments involving manganous chloride and manganous sulfate, the oral toxicity of manganese is low largely because of restricted absorption and the existence of a relatively efficient mechanism regulating intestinal excretion.
Manganese interacts metabolically with several other minerals including calcium, phosphorous, iron, and copper. Under most conditions, however, it is unlikely that the ratio of manganese to these elements is distorted enough to produce an adverse effect.
The only manganese salts known by the Select Committe to be in use as ingredients of foods for human consumption are the chloride and the sulfate. Despite the nearly complete lack of scientific reports on the biologic effects of manganous citrate and gluconate, the relatively low toxicity of the manganous ion and the innocuous nature of citrates and gluconates when used as food ingredients suggest that no health hazard would result from similar uses of manganous citrate and gluconate.
While there is good evidence of the short-term tolerance of manganous oxide as an added feed ingredient for poultry and livestock, no acute oral toxicity studies or long-term feeding studies of manganous oxide have been reported. In addition, the Select Committee has no information on the amounts of manganous oxide, if any, that may be use in food for human consumption in this country.
The Select Committe has weighed the foregoing data and concludes that: There is no evidence in the availble information on manganous citrate, chloride, gluconate, and sulfate that demonstrates, or suggests reasonable grounds to suspect, a hazard to the public when they are used at levels that are now current or that might reasonable be expected in the future. In view of the deficiency of relevant biological studies and information on consumer exposure, the Select Committee has insufficient data upon which to base an evaluation of manganous oxide when it is used in food for human consumption.