Manganese: Benefits, Dosage, and Safety

What manganese is

Manganese is an essential trace element naturally present in many foods and available as a dietary supplement. It is a cofactor for many enzymes, including manganese superoxide dismutase, arginase, and pyruvate carboxylase. The human body contains about 10 to 20 mg of manganese, of which 25% to 40% is in bone, with the rest concentrated in the liver, pancreas, kidney, and brain. Humans absorb only about 1% to 5% of dietary manganese in the small intestine, and more than 90% of absorbed manganese is excreted via bile into the feces. Because intake and excretion are tightly regulated, the body maintains stable tissue concentrations.

What it does

• Serves as a cofactor for many enzymes, including manganese superoxide dismutase, arginase, and pyruvate carboxylase
• Involved in amino acid, cholesterol, glucose, and carbohydrate metabolism
• Contributes to reactive oxygen species scavenging (antioxidant defense)
• Involved in bone formation
• Involved in reproduction and immune response
• Plays a role in blood clotting and hemostasis in conjunction with vitamin K

How much manganese per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Manganese deficiency is very rare in humans, and signs and symptoms of deficiency have not been firmly established. The very limited evidence in humans suggests deficiency might cause bone demineralization and poor growth in children; skin rashes, hair depigmentation, decreased serum cholesterol, and increased alkaline phosphatase activity in men; and altered mood and increased premenstrual pain in women. Deficiency might also alter lipid and carbohydrate metabolism and cause abnormal glucose tolerance.

Who may need more

• Most people obtain adequate manganese from a normal diet; ODS states no known groups are likely to have inadequate intakes
• Infants should get manganese only from breast milk, formula, and food (no supplements)
• People with chronic liver disease should be cautious, as impaired biliary excretion raises the risk of manganese accumulation and neurotoxicity
• People with iron deficiency absorb more manganese and may be more vulnerable to excess

Food sources

Manganese is found in a wide variety of foods, especially whole grains, clams, oysters and mussels, nuts, soybeans and other legumes, rice, leafy vegetables, coffee, tea, and many spices such as black pepper. Top sources in U.S. adult diets are grain products, tea, and vegetables. Examples per serving: cooked blue mussels 3 oz (5.8 mg, 252% DV), dry roasted hazelnuts 1 oz (1.6 mg), dry roasted pecans 1 oz (1.1 mg), cooked medium-grain brown rice 1/2 cup (1.1 mg), cooked chickpeas 1/2 cup (0.9 mg), boiled spinach 1/2 cup (0.8 mg), and 1 slice whole wheat bread (0.7 mg). The Daily Value (DV) for manganese is 2.3 mg.

Forms and absorption

In dietary supplements, manganese is present in many forms, including amino acid chelates (manganese bisglycinate chelate, manganese glycinate chelate, manganese aspartate) and manganese gluconate, picolinate, sulfate, citrate, and chloride. No data are available on the relative bioavailability of the different supplemental forms. Supplement Facts labels declare the amount of elemental manganese, not the weight of the whole compound. Multivitamin/mineral products that contain manganese typically provide 1.0 to 4.5 mg, while manganese-only or manganese-focused supplements most often contain 5 to 20 mg.

Safety, excess and interactions

Too much

No evidence shows manganese toxicity from high dietary manganese intakes. Toxicity has occurred through chronic inhalation of manganese dust in occupations such as welding and mining, and in people consuming water with high manganese levels (in some cases as high as 28 mg/L). Toxicity mainly affects the central nervous system and can cause tremors, muscle spasms, tinnitus, hearing loss, and a feeling of being unsteady on one's feet. Additional symptoms include mania, insomnia, depression, delusions, anorexia, headaches, irritability, lower extremity weakness, changes in mood and short-term memory, altered reaction times, and reduced hand-eye coordination. These can progress to neuromotor impairments similar to Parkinson's disease, including changes in gait and balance, tremor, and rigidity. Iron deficiency increases manganese absorption and can exacerbate toxicity, and people with chronic liver disease have impaired biliary manganese elimination and are more susceptible to neurotoxicity.

Interactions to know

• ODS states manganese is not known to have any clinically relevant interactions with medications
• Nutrient interaction: dietary iron intake and iron status (serum ferritin) are inversely associated with manganese absorption; low iron status increases manganese absorption and can exacerbate manganese toxicity
• Nutrient interaction: iron and manganese appear to share an intestinal transporter, which may underlie their competitive absorption

How status is measured

Manganese status is difficult to assess and not routinely measured in clinical practice. Normal whole blood concentrations range from 4 to 15 mcg/L but are highly variable, and their utility as a status indicator is unclear. Serum and plasma concentrations (mean serum about 1.04 mcg/L, mean plasma about 1.28 mcg/L in healthy adults) often do not correlate well with typical intakes. Urinary manganese decreases with severe deficiency but is not a clear indicator within the normal intake range.

Regulated as a dietary supplement ingredient under the Dietary Supplement Health and Education Act (DSHEA), not reviewed by FDA for safety or efficacy before marketing. FDA has set a Daily Value (DV) for manganese of 2.3 mg for adults and children age 4 and older; food labels are not required to list manganese unless it has been added to the food.

What the evidence supports

We grade the strength of evidence behind each common reason people take manganese, mirroring how the NIH describes it.