Manganese plays an indispensable role in human physiology. Minerals are categorized based on the amount required by the body: macrominerals, needed in larger quantities, and micronutrients, required in trace amounts. Manganese belongs to the latter group, despite its various functions across many bodily systems. A consistent, albeit small, intake of this element is necessary for health.
Defining Manganese as an Essential Trace Element
Manganese is classified as an essential trace element, or micronutrient. This means the body cannot produce it and it must be obtained entirely through diet to support normal function. The “trace” designation applies because the body requires only very small quantities, typically in the range of milligrams or micrograms per day, unlike major minerals such as calcium.
The total amount of manganese stored in the human body is low, estimated to be between 10 to 20 milligrams, with a significant portion concentrated in the bone. The liver, kidneys, and pancreas also store smaller, metabolically active amounts. This small required intake level places it firmly in the category of essential trace elements.
Manganese’s Role in Metabolism and Enzyme Activation
The primary biological function of manganese is its role as a cofactor for a variety of enzymes. These metalloenzymes speed up chemical reactions involved in nearly all metabolic processes within the body. Without manganese, these enzymes cannot perform their functions efficiently.
One intensely studied manganese-dependent enzyme is Manganese Superoxide Dismutase (MnSOD), localized within the mitochondria, the cell’s powerhouses. MnSOD is a major antioxidant defense, converting the harmful superoxide radical into less reactive hydrogen peroxide. This protects the cell from oxidative damage, which is important because energy production in the mitochondria generates many reactive molecules.
Manganese also serves as a cofactor for enzymes involved in the metabolism of major nutrients, including carbohydrates, amino acids, and cholesterol. For instance, it is a component of pyruvate carboxylase and arginase, which play roles in energy production and the urea cycle. Furthermore, manganese is involved in bone and cartilage formation by activating glycosyltransferases, necessary for synthesizing connective tissue proteoglycans.
Common Dietary Sources and Recommended Intake
Manganese is widely available, particularly in plant-based sources. Rich sources include whole grains, nuts, legumes, and leafy green vegetables like spinach. Tea is also a high contributor to dietary manganese intake in many populations.
The Recommended Dietary Allowance (RDA) for manganese is set as an Adequate Intake (AI) due to insufficient data to establish a precise requirement. The AI is 2.3 milligrams per day for adult men and 1.8 milligrams per day for adult women. These levels ensure the body has adequate manganese to support its numerous metalloenzymes.
The body absorbs a low amount of manganese from food, typically between 1% to 5% of the total ingested amount. High intakes of other nutrients, such as iron and calcium, may slightly inhibit absorption due to competition for transport pathways. However, consuming a balanced diet rich in whole foods generally ensures sufficient intake for most healthy individuals.
Understanding Imbalances Too Little and Too Much
Manganese deficiency is rare in humans because it is widespread in common foods, though it can occur under certain clinical conditions. Signs of deficiency are not firmly established but may include impaired growth, poor bone formation, and altered carbohydrate and lipid metabolism. These symptoms relate to the element’s role as an enzyme cofactor in these processes.
Excessive manganese intake primarily affects the central nervous system. Toxicity rarely results from diet alone, as the body tightly regulates absorption and excretion via the bile. The Tolerable Upper Intake Level (UL) for adults is set at 11 milligrams per day.
Toxicity is most often observed following chronic inhalation exposure in occupational settings, such as mining or welding, a condition called manganism. Symptoms are neurological and can resemble Parkinson’s disease, including tremors, difficulty walking, and muscle spasms. Individuals with liver disease are more susceptible to toxicity because their ability to excrete manganese through bile is impaired.