Manganese is an essential trace element; it’s needed for good health but is only required in tiny amounts. The Ministry of Health, Labour and Welfate (MHLW) has set an adequate intake (AI) of 4.0mg/day for males and 3.5mg/day for females. Both the FDA and EFSA have established AIs of 3mg/day or below for adults[2, 3]. Manganese deficiency is rare, and the symptoms are not well established. It’s possible that a lack of manganese causes bone demineralisation and skin rashes.
Manganese is involved in the metabolism of food to produce energy as it acts as a cofactor for several enzymes. It also has pro- and antioxidant activities. Manganese is one of the required compounds for manganese superoxide dismutase which is a major scavenger of reactive oxygen species in cells.
Manganese toxicity is partly attributable to its prooxidant activity, which can cause oxidative stress that the body can’t cope with.
Most manganese toxicity cases come from inhalation of manganese in industry and mining over months and years. This is because inhaled manganese can enter the bloodstream and avoid the liver, which would usually cause the excretion of a significant proportion of the manganese.
There is limited evidence that intake of water high in manganese may be associated with neurological symptoms, but this has only occurred in areas where the drinking water was contaminated with manganese. Plus, manganese in drinking water may be more bioavailable than that in food.
Nutritionally, manganese is one of the least toxic elements because, when excess is consumed, absorption is very low and that which is absorbed is efficiently excreted via bile and the kidneys.
It has been shown that plant-based diets, such as the Ornish diet, can provide on average 11.5mg of manganese per day. This is above the upper limit of 11mg/day set by Japan and the US, based purely on the highest levels (10.9mg/day) presented in studies. The EU has no upper limit due to insufficient evidence. Yet there is a distinct lack of adverse effects reported as a result of higher levels of consumption[11, 12]. Part of this could be explained by the presence of antinutrients and other micronutrients, such as iron which affect the bioavailability of manganese.
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