Manganese: Safety Assessment

The United Kingdom Expert Group on Vitamins and Minerals (EVM) last assessed vitamins and minerals for safety in 2003 and set a so-called Safe Upper Level (SUL) or Guidance Level for each micronutrient, provided sufficient data were available. This SUL or Guidance Level reflects the safe maximum amount of a micronutrient that will not cause any side effects when taken daily from all sources for a lifetime.

The maximum safe daily intake for manganese is 12.2 mg. The maximum safe daily intake for manganese is 6 times the EU recommended daily intake (Nutrient Reference Value, NRV).

The above safe daily intake is composed of an assumed intake of 8.2 mg from the conventional diet and an additional intake of 4 mg of manganese from dietary supplements that is considered safe. It does not apply to older people 50 years and older. Because of greater susceptibility to neurologic disorders, a daily manganese intake of only 8.7 mg is considered safe for the elderly 50 years and older.

A manganese concentration of 0.75 mg per liter of drinking water did not result in any adverse effects when consumed at a sustained rate of 2 liters per day in addition to the conventional diet. Amounts of 0.6 to 4.3 mg of manganese from drinking water per day in addition to the conventional diet, ingested over 10 to 40 years, also remained without adverse effects.

The NOAEL (No Observed Adverse Effect Level) – the highest dose of a substance that has no detectable and measurable adverse effects even with continued intake – was set by EVM at 4 mg of manganese daily from dietary supplements, in addition to the conventional diet.

Adverse effects of excessive manganese intake are primarily nerve disorders, caused by exposure to manganese-containing dusts in the workplace and by ingestion of contaminated drinking water.

Occupational exposure to manganese-containing workplace dusts, after prolonged inhalation, resulted in myalgia (muscle pain), general weakness, slowed movement, loss of appetite, and speech disorders, and even “manganism,” a nervous disorder similar to Parkinson’s disease. The WHO (World Health Organization) assumes that the threshold dose for neurological effects is between 0.1 mg manganese/m³ air and 1 mg manganese/m³ air. However, the route of inhalation is secondary to the safety assessment of manganese from food.

Continuous consumption of drinking water containing manganese also resulted in neurological disorders such as myalgia (muscle pain), general weakness, tremor (shaking), memory impairment, and impaired reflexes. In Japan, contaminated drinking water containing 14 mg of manganese per liter resulted in severe poisoning symptoms such as tremors and mental disorders and, in two cases, death. Another study also observed neurological disorders after ingestion of at least 28 mg of manganese from drinking water in addition to the conventional diet.

In a study of elderly people aged 50 and older, adverse side effects such as depression, fatigue, hallucinations, tremors, and impaired reflexes occurred at levels as low as 3.6 to 4.6 mg per day of manganese from drinking water in addition to the conventional diet. However, dietary manganese intake was not determined, making total manganese intake unknown. Therefore, for the elderly 50 years of age and older, the above safe daily intake limit of 8.7 mg of manganese from all sources has been established.