We need small amounts of manganese for stronger bones and sharper brains. It may also protect against depression, seizures, diabetes, and cancer, but beware when supplementing with this metal, because higher doses can be toxic.
- Energy (ATP) production (in mitochondria) 
- Antioxidant defense 
- Fat, protein, and sugar metabolism [1, 2]
- Brain development and function 
- Immune response 
- Sex hormone production and reproductive function [2, 7]
- Digestion 
- Bone and connective tissue production [2, 7]
Because it’s found pretty much everywhere, you’re more likely to have excess manganese than to be deficient.
Keep in mind that this section discusses the biological role of manganese, and not necessarily the benefits of taking manganese supplements. These functions may suffer if someone is deficient in manganese, but more is not always better, as too much manganese can be harmful. If you are concerned about your manganese intake, talk to your doctor to see if increased dietary manganese intake is a good idea for you.
Manganese superoxide dismutase (MnSOD) is the cell’s most important antioxidant enzyme. It neutralizes the toxic effects of reactive oxygen species (ROS) in mitochondria. MnSOD also protects cells from inflammation and cancer-causing agents, such as toxic chemicals and radioactive materials [10, 8, 11].
If you are deficient in manganese, you will have reduced MnSOD activity, which leads to cellular damage and dysfunction .
Several enzymes important for brain function work only in the presence of manganese .
In another study of 404 school-age children, those with very low or very high blood and hair levels of manganese had lower IQ scores. Children in the middle of the scale, with roughly average blood and hair levels of manganese, had the highest IQ scores .
Finally, in a study of over 1,200 children, girls that had higher exposure to manganese before they were born performed better in cognitive tests. However, in the same study, high manganese exposure in early life adversely affected children’s behavior. Once again, balanced manganese levels are important .
In a study of over 2,000 Japanese people, low dietary manganese was associated with a higher risk of depression. Similarly, in another study of 1,745 pregnant Japanese women, those with higher manganese intake were less likely to experience depressive symptoms during pregnancy [17, 18].
Manganese superoxide dismutase (MnSOD) likely plays a role. In a study of 236 people, those who had experienced multiple episodes of depression had lower levels of MnSOD .
In both humans and animals, there is a link between low blood manganese and seizures .
Some studies suggest that neurological symptoms in epileptics may correlate with low brain manganese. However, it’s not clear if low levels of manganese make people more likely to experience seizures, or if seizures deplete manganese levels [21, 20].
A U.S. study found that children with autism had marginally lower levels of tooth manganese, which reflects their exposure to this metal .
Autism is associated with an increase of glutamate in the brain . Glutamine synthetase, an enzyme that converts glutamate into glutamine, contains manganese . Therefore, manganese deficiency may result in higher brain glutamate.
Furthermore, mitochondrial dysfunction is a key feature of autism. Manganese superoxide dismutase (MnSOD) protects the mitochondria from oxidative damage and dysfunction; if autistic people are deficient in manganese, they will not produce enough MnSOD to protect their mitochondria .
Finally, people with autism have low levels of beneficial Lactobacillus bacteria in their gut. These bacteria depend on manganese for antioxidant protection. Given enough manganese, Lactobacillus probiotics can lower the anxiety people with autism often experience .
According to a meta-analysis of 17 studies with over 2000 people, patients with Alzheimer’s disease have significantly lower blood manganese levels compared to their healthy counterparts. Therefore, manganese deficiency may be a risk factor for Alzheimer’s, but causal proof is still missing .
Mitochondrial dysfunction and an increase of glutamate in the brain are also associated with Alzheimer’s disease. As discussed in the section on autism, both of these can be associated with manganese deficiency .
Some genetic disorders make it difficult for people’s cells to transport manganese. This type of manganese deficiency can cause short stature, also known as dwarfism, likely due to bone growth issues [28, 29].
Manganese supplementation effectively reduces the loss of bone mass in female rat models of postmenopausal osteoporosis .
In multiple animal studies, diets low in manganese interfered with cartilage production and resulted in low bone density .
Both male and female animals experience reduced fertility if they are manganese deficient: females develop ovulation issues, while the testicles of males may degenerate .
In a study of 96 women, those with premenstrual syndrome (PMS) had lower blood manganese levels. In a small-scale study, reducing dietary manganese intensified mood and pain symptoms during PMS in 10 women [33, 34].
However, a larger study of over 3000 women found no relationship between manganese and PMS .
In a large study of over 10,000 people, higher manganese intake in the diet was associated with a lower incidence of type 2 diabetes and lower levels of HbA1c, an important marker of long-term blood sugar .
However, another study of 3200 people found a U-shaped association between blood manganese levels and diabetes. That is, diabetes risk increased for both the lowest and highest levels of manganese .
Metabolic syndrome is a cluster of conditions that occur together and increase your risk of heart disease and diabetes. You have metabolic syndrome if you have three of the following :
- high blood pressure
- high blood sugar
- excess body fat around the waist
- high bad cholesterol or triglyceride levels
- low good cholesterol
In a study of 550 Chinese adults, those with higher manganese intake in their diets had a significantly lower risk of developing metabolic syndrome .
In another study of over 2000 Chinese adults, men with a higher manganese intake were less obese and had lower blood triglycerides. However, higher manganese intake was also associated with low HDL (good) cholesterol in both men and women .
Meanwhile, in over 5000 Korean adults, women who had metabolic syndrome had lower daily intakes of manganese .
In a study of over 3800 people, higher urinary manganese was linked with lower systolic and diastolic blood pressure. In another study of 255 people, mid-range manganese levels were associated with lower blood pressure [49, 50].
In animals, when the mother is deficient in manganese, the offspring are more susceptible to high-fat-diet-induced obesity, high cholesterol, and inflammation .
However, it’s difficult to confirm the association between dietary manganese intake and metabolic syndrome. It may be the case, for example, that people who eat a healthier diet also happen to have higher manganese levels.
In fact, people eating plant-based diets (e.g. vegetarians) naturally have higher manganese intakes because plant foods are higher in manganese. These diets are linked with lower cholesterol and fewer metabolic issues, but not necessarily because of their manganese content [52, 53].
According to a meta-analysis of 11 studies with over 1300 people, women with breast cancer had lower manganese levels than healthy women .
In support of these findings, the level of MnSOD gets reduced prior to the formation of cancer in mice .
This enzyme may help fight many types of cancer, but not all of them. Many human cancers have low levels of MnSOD. However, some cancers actually have high levels of this enzyme .
A combination of proteins containing manganese improved the appearance of several signs of skin damage from the sun in 15 female subjects. The treatment, applied directly to the skin, significantly improved hyperpigmentation, or the appearance of patchy dark spots .
We get most of our manganese through our diet .
Legumes, rice, nuts, and whole grains contain the highest levels of manganese. This metal is also found in seafood, seeds, chocolate, tea, leafy green vegetables, spices, soybeans, and some fruits such as pineapple, blueberries, and acai. A cup of tea contains as much as 1.3 mg of manganese [58, 5, 2, 22, 59].
The adult dietary intake of manganese is normally anywhere from 0.9 to 10 mg per day. The US National Research Council has established an estimated safe and adequate dietary intake of 2-5 mg/day for adults [59, 6, 22, 60].
Most people already have more than an adequate intake of manganese and should be careful when supplementing this metal. People eating vegetarian diets and Western-type diets may have manganese intakes as high as 10.9 mg/day, close to the upper safe limit from all sources .
Commercial supplements usually contain 5-20 mg of manganese .
Bear in mind that 11 mg/day is often cited as the upper safe limit (where no adverse effects are observed) for manganese. We therefore recommend against using manganese supplements without the recommendation of a medical professional.
Manganese is an essential mineral that supports antioxidant enzymes like superoxide dismutase. Without it, oxidative stress may run rampant, and the bones and brain cannot properly grow and function.
Most people get more than enough dietary manganese from plant-based foods like legumes, leafy green vegetables, nuts, and whole grains. The safe upper limit of manganese is about 11 mg per day; because of the potential for toxicity, we recommend talking to a doctor before supplementing.
Want to learn more about manganese deficiency and the best ways to increase your intake? Check out our post here.