Manganese — Health Benefits, Rich Foods, Toxicity, and More
Introduction
Manganese (Mn) is an essential trace mineral that plays a vital role in various physiological processes in the human body. While often overlooked compared to other minerals, such as iron or calcium, manganese is crucial for overall health and well-being.
This article explores the importance of manganese in nutrition, its health benefits, dietary sources, and potential risks associated with deficiency or excess intake.
Table of contents
Absorption, Metabolism, and Regulation
Manganese can be absorbed through ingestion, inhalation, skin, and intravenous (IV) injection.
Manganese in food and water is quickly absorbed in the gastrointestinal tract and transported through the bloodstream to tissues such as the liver, pancreas, bone, kidney, and brain. Manganese accumulates in organs high in cellular mitochondria (1, 2).
Manganese is absorbed in the intestines through passive diffusion or active transport with the help of cellular metal transporters. However, these transporters also play a role in the absorption of other metals, such as iron, calcium, copper, and zinc. Thus, these metals compete with manganese absorption (1).
Manganese is an essential component of manganese superoxide dismutase, which plays a vital role in mitigating mitochondrial oxidative stress. Mitochondria serve as the primary site for the generation of both physiological and pathological cellular reactive oxygen species (2).
Manganese absorption rates are typically higher in females compared to males, and this difference may be influenced by iron status. Manganese absorption increases when iron levels are lower (1).
The liver is the main organ that regulates manganese levels in the body by helping to remove excess manganese through the digestive system in the produced bile. Manganese is also eliminated from the body through urine, milk, and sweat, although in very small quantities (1).
Recommended Intakes
The typical manganese intake in Western diets ranges from 2.3 to 8.8 mg per day (3).
The table below shows the current adequate intake of manganese (4).
| Up to 6 months | 7 to 12 months | 1 to 3 years | 4 to 8 years | 9 to 13 years | 14 to 18 years | Above 19 | |
| Male | 0.003mg | 0.6mg | 1.2mg | 1.5mg | 1.9mg | 2.2mg | 2.3mg |
| Female | 0.003mg | 0.6mg | 1.2mg | 1.5mg | 1.6mg | 1.6mg | 1.8mg |
Thus, the adequate daily intake of manganese for people above the age of 19 is 1.8mg for females and 2.3mg for males. These values increase to 2mg and 2.6mg during pregnancy and lactation, respectively (4).
The WHO recommends the manganese content of water to be below 400mcg/L. Water intake with higher manganese levels was associated with declined academic achievement (5).
Foods Rich in Manganese
Shellfish, nuts, seeds, whole grains, legumes, leafy green vegetables, tea, and certain fruits like pineapple, blueberries, and raspberries are among the foods rich in manganese.
Below, you can find a list of foods high in manganese based on their average serving sizes.
| Food Name | Manganese Content | Serving Size |
| Mussels (blue, cooked) | 5.8mg | 85g or 3 ounces |
| Brown rice (long-grain cooked) | 1.97mg | 202g or 1 cup |
| Hazelnuts | 1.75mg | 28.35g or 21 whole kernels |
| Chickpeas (cooked) | 1.69mg | 164g or 1 cup |
| Spinach (cooked) | 1.68mg | 180g or 1 cup |
| Pineapple (raw) | 1.5mg | 165g or 1 cup in chunks |
| Tofu (raw) | 1.5mg | 126g or 0.5 cup |
| Soybeans (cooked) | 1.42mg | 172g or 1 cup |
| Raspberries | 0.82mg | 123g or 1 cup |
| Tea (black) | 0.39mg | 178g or 6 fluid ounces |
Other food sources of manganese include oysters, clams, pecans, peanuts, sweet potatoes, lima beans, lentils, black pepper, oatmeal, bread, pumpkin seeds, and sesame seeds.
Drinking water is also a source of manganese.
Health Benefits and Functions of Manganese
Manganese serves as a vital nutrient for numerous intracellular processes, acting as a cofactor for various enzymes such as arginase, glutamine synthetase, pyruvate carboxylase, and manganese superoxide dismutase.
These metalloproteins facilitated by manganese are indispensable for functions related to development, digestion, reproduction, antioxidant defense, energy generation, immune function, and the regulation of neuronal activities (1).
Diabetes
Numerous studies have identified links between both elevated and reduced manganese levels in the blood and the occurrence of type 2 diabetes (6).
One research, including about 1600 adults with type 2 diabetes and 1600 adults without diabetes, found that people with the lowest magnesium levels were 1.9 times more likely, and those with the highest magnesium levels were 1.6 times more likely to develop type 2 diabetes (7).
Animal studies show that manganese supplementation could enhance glucose tolerance, diminish oxidative stress, and ameliorate endothelial dysfunction in diabetes. However, human clinical trials to prove these findings are lacking (6).
Multiple pathways implicated in diabetes, including the generation of reactive oxygen species (ROS) triggered by elevated glucose levels, contribute to metabolic irregularities and chronic complications. Additionally, oxidative stress can impair the function of pancreatic beta cells, promote insulin resistance, and ultimately contribute to the development of type 2 diabetes and obesity. Manganese helps maintain mitochondrial ROS levels within a normal range, which can help prevent these adverse effects (2).
Metabolic Syndrome and Obesity
Oxidative stress and the production of reactive oxygen species have been associated with the development of not only insulin resistance and type 2 diabetes but also obesity (2).
Animal studies have shown that obese mice exhibited significantly lower concentrations of manganese in the liver, small intestine, and bone compared to lean mice (8).
Conversely, a study involving 5404 children and adolescents aged 6 to 19 years found that the highest blood manganese concentration was associated with obesity and excess weight (9).
Metabolic syndrome refers to a condition characterized by a cluster of risk factors specific to cardiovascular disease. These factors include abdominal obesity, high blood pressure, impaired fasting glucose, elevated triglyceride levels, and low levels of high-density lipoprotein (HDL) cholesterol.
Higher manganese intake was linked to a reduced risk of metabolic syndrome in men but an increased risk in women. Chinese researchers also observed that manganese intake was inversely associated with metabolic syndrome components such as abdominal obesity and high triglycerides in men and positively associated with low HDL-cholesterol (“good cholesterol”) in both men and women (2).
Atherosclerosis
Manganese supplementation has shown promise in reducing high glucose-induced monocyte adhesion to endothelial cells, improving endothelial function, and reducing cholesterol levels in the blood. In simpler words, it exhibits anti-inflammatory effects in endothelial cells and may help prevent or delay the progression of atherosclerosis (2).
However, one study found higher levels of magnesium in the elderly who have atherosclerosis (10).
Bone Health
Manganese serves as a cofactor for numerous enzymes engaged in bone formation. A lack of manganese can hinder bone formation and decrease bone mineral density in animals, while manganese supplementation has been shown to enhance both bone mineral density and bone formation (6).
However, researchers studying potential connections between manganese levels in the bloodstream, bone mineral density, and osteoporosis in humans, find the available evidence to be sparse and inconclusive (6).
Neurodegenerative Diseases
Manganese has been implicated in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer’s disease, and Huntington’s disease (11).
In ALS, oxidative stress is thought to contribute to manganese-related neurotoxicity, although the exact mechanisms are still being investigated. Similarly, in Alzheimer’s disease, manganese accumulation in the brain has been linked to cognitive impairment and neuronal degeneration, possibly through interactions with amyloid-beta precursor proteins.
Research on Huntington’s disease involves a gene-environment interaction between mutant Huntington protein expression and manganese exposure, with mutant cells showing reduced vulnerability to manganese toxicity compared to wild-type cells.
These findings highlight magnesium's complex role in neurodegenerative diseases and the need for further research to elucidate its mechanisms of action
Manganese Deficiency
Normal manganese concentrations in human blood typically range from 4 to 15 mg/L. Moreover, women tend to have approximately 30% higher manganese levels than men (1). Manganese levels below this range lead to deficiency.
However, manganese deficiency is very uncommon in humans, and the specific signs and symptoms of this deficiency have not been definitively identified. Research finds that a lack of manganese might lead to bone demineralization and stunted growth in children, skin issues and hair discoloration in men, as well as changes in mood and increased menstrual discomfort in women (6).
Additionally, manganese deficiency could potentially affect lipid and carbohydrate metabolism, leading to abnormal glucose tolerance (6).
Manganese Supplements
Various multivitamin/mineral and dietary supplements include manganese in their formulations. These supplements contain different manganese compounds, such as manganese sulfate, manganese aspartate, manganese gluconate, manganese citrate, and manganese citrate.
Manganese can also come in the form of amino acid chelates, such as manganese bisglycinate chelate, manganese glycinate chelate, and manganese aspartate (6).
While not all multivitamin/mineral supplements contain manganese, those that do usually offer doses ranging from 1.0 to 4.5 mg of manganese. There are also supplements solely focused on manganese or combining manganese with a few other nutrients, typically providing 5 to 20 mg of manganese (6).
Manganese Toxicity or Manganism
An excess of manganese tends to accumulate in several organs, including the liver, pancreas, bone, kidney, and notably, the brain, which is the primary site affected by manganese intoxication. Neurons are particularly vulnerable to manganese intoxication, likely because of their extended lifespan and heightened energy needs (1).
Manganism, also known as locura manganica, has been recognized for 150 years. It occurs due to the accumulation of manganese in brain regions abundant in dopaminergic neurons, such as the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nuclei. Manganese can easily oxidize catecholamines like dopamine, disrupting homeostasis in these brain areas (11).
The Tolerable Upper Intake Level (UL) represents the maximum daily intake considered unlikely to result in adverse health effects. The UL for manganese in adults aged 19 and above, as well as in pregnant and lactating women, is set at 11mg per day. This value is 9mg for people aged 14 to 18 (4, 12).
Manganese toxicity occurs more often than manganese deficiency, which is not the case with most other minerals.
Causes
There is no evidence indicating manganese toxicity resulting from high dietary manganese intake (6).
The majority of clinically reported cases of manganese intoxication stem from occupational exposure. Inhaling airborne manganese represents the primary route of exposure in cases of occupational manganese intoxication (1).
Industrial workers, particularly miners, smelters, and welders, are exposed to substantial amounts of manganese-containing fumes and dust, making them the adult population most susceptible to manganese-induced toxicity (1, 2).
Symptoms
Exposure to manganese can result in clinical manifestations that resemble Parkinson's disease, although they are separate disorders.
Early manganism stages show psychiatric symptoms like emotional instability, aggression, hallucinations, and intellectual deficits, along with mild motor impairment. As manganism progresses, classic extrapyramidal or motor symptoms emerge, including mask-like face, limb rigidity, tremors, gait disturbance, slurred speech, and balance issues (11).
In the early stages of manganism, if manganese exposure is stopped, symptoms may be reversible. However, in patients with motor disturbances, manganism tends to be irreversible (11).
Interactions With Medications
Manganese is not recognized to have any clinically significant interactions with medications (6).
Summary
Manganese (Mn) is an essential trace mineral that plays a vital role in various physiological processes in the human body.
Manganese in food and water is quickly absorbed in the gastrointestinal tract and transported through the bloodstream to tissues such as the liver, pancreas, bone, kidney, and brain.
The adequate daily intake of manganese for people above the age of 19 is 1.8mg for females and 2.3mg for males. These values increase to 2mg and 2.6mg during pregnancy and lactation, respectively.
Shellfish, nuts, seeds, whole grains, legumes, leafy green vegetables, tea, and certain fruits like pineapple, blueberries, and raspberries are among the foods rich in manganese.
Manganese facilitates the formation of metalloproteins, which are indispensable for functions related to development, digestion, reproduction, antioxidant defense, energy generation, immune function, and the regulation of neuronal activities.
Maintaining manganese levels within the normal range has been associated with a reduced risk of developing type 2 diabetes, obesity, and atherosclerosis, according to research findings.
Manganese toxicity is more common than manganese deficiency. Excessive manganese accumulation in organs, particularly the brain, leads to manganism.
Occupational exposure, particularly among industrial workers like miners, smelters, and welders, represents the primary source of manganese toxicity, with symptoms ranging from psychiatric manifestations to classic motor impairments resembling Parkinson's disease, which may become irreversible in advanced stages.
References
- https://www.researchgate.net/publication/323487276
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5907490/
- https://pubmed.ncbi.nlm.nih.gov/26231508/
- https://www.ncbi.nlm.nih.gov/books/NBK222332/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3282923/
- https://ods.od.nih.gov/factsheets/Manganese-HealthProfessional/
- https://pubmed.ncbi.nlm.nih.gov/27258818/
- https://pubmed.ncbi.nlm.nih.gov/3761000/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5331535/
- https://pubmed.ncbi.nlm.nih.gov/23245729/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6589086/
- https://www.hsph.harvard.edu/nutritionsource/manganese
