Manganese

Manganese is an essential trace mineral that the body requires in very small amounts—typically only a few milligrams per day. Despite being a "trace" mineral, it plays critical roles in several physiological processes as a cofactor for key enzymes.

The body contains only about 10-20 milligrams of manganese, concentrated primarily in bones, liver, pancreas, and kidneys. It is absorbed in the small intestine and transported to tissues bound to transferrin and other plasma proteins.

Manganese serves as an essential cofactor for several enzymes:

1. Manganese Superoxide Dismutase (MnSOD): The primary antioxidant enzyme in mitochondria, protecting cells from oxidative damage by converting superoxide radicals to hydrogen peroxide.

2. Arginase: An enzyme in the urea cycle that helps remove ammonia from the body.

3. Pyruvate Carboxylase: Involved in gluconeogenesis (glucose production).

4. Glutamine Synthetase: Important for amino acid metabolism and ammonia detoxification.

5. Glycosyltransferases: Enzymes involved in bone and cartilage formation through glycosaminoglycan synthesis.

Through these enzymes, manganese is involved in:

• Bone formation: Required for proper bone mineralization and cartilage development
• Antioxidant defense: Protects cells from oxidative stress via MnSOD
• Carbohydrate metabolism: Involved in glucose metabolism and insulin function
• Amino acid metabolism: Required for protein synthesis and ammonia detoxification
• Cholesterol metabolism: Involved in cholesterol synthesis
• Wound healing: Important for collagen formation

Manganese deficiency is extremely rare in humans because the mineral is widely distributed in foods, particularly whole grains, nuts, legumes, and tea. The body also efficiently conserves manganese when intake is low.

While deficiency is rare, manganese is an established essential nutrient with defined Adequate Intake (AI) levels. Most people obtain sufficient manganese from their diet, making supplementation generally unnecessary unless under medical supervision for specific conditions.

Of note, excessive manganese intake can be neurotoxic, particularly affecting the basal ganglia. This is primarily a concern with occupational exposure or contaminated water sources, not dietary intake or typical supplementation.

Manganese functions primarily as an essential cofactor (coenzyme) for several metalloenzymes and as an activator for other enzymes:

1. Manganese Superoxide Dismutase (MnSOD): This is the most important manganese-dependent enzyme, located in mitochondria. It catalyzes the conversion of superoxide radicals (O₂⁻) to hydrogen peroxide (H₂O₂) and oxygen:

• Protects mitochondria from oxidative damage
• Essential for cellular antioxidant defense
• Manganese is required at the active site of the enzyme
• Without adequate manganese, MnSOD activity is impaired

2. Arginase: Catalyzes the conversion of arginine to ornithine and urea:

• Critical for the urea cycle (ammonia detoxification)
• Regulates nitric oxide production by competing with nitric oxide synthase
• Important for liver function

3. Pyruvate Carboxylase: Converts pyruvate to oxaloacetate:

• Essential for gluconeogenesis (glucose synthesis)
• Involved in energy metabolism
• Important during fasting or low-carbohydrate conditions

4. Glycosyltransferases: A family of enzymes requiring manganese:

• Synthesize glycosaminoglycans (GAGs) and proteoglycans
• Critical for cartilage and bone matrix formation
• Required for collagen structure
• Essential for connective tissue integrity

5. Glutamine Synthetase: Incorporates ammonia into glutamate to form glutamine:

• Important for nitrogen metabolism
• Ammonia detoxification in the brain
• Neurotransmitter synthesis

6. Xylosyltransferases: Required for glycosaminoglycan chain initiation:

• Essential for proteoglycan synthesis
• Critical for cartilage formation

7. Prolidase: Involved in collagen metabolism and recycling:

• Releases proline from peptides
• Important for wound healing and tissue repair

Absorption and Transport: Manganese is absorbed in the small intestine through active transport (when levels are low) and passive diffusion (when levels are high). Iron deficiency increases manganese absorption, which can lead to toxicity concerns. Manganese is transported in blood bound to transferrin and albumin, and distributed to tissues where it accumulates primarily in mitochondria-rich organs.

Manganese is widely distributed in foods, with particularly high concentrations in whole grains, nuts, legumes, seeds, and tea. Whole grains contain more manganese than refined grains because the mineral is concentrated in the bran and germ. Leafy vegetables, pineapple, and shellfish also provide good amounts. Tea is an exceptionally rich source, with black tea providing significant amounts per cup.

Manganese deficiency is extremely rare in humans because the mineral is widely available in foods and efficiently conserved by the body. Experimental deficiency has been induced in studies but is not a clinical concern in free-living populations. Deficiency would affect bone development, antioxidant capacity, and metabolism.

AI (Adequate Intake) established by NIH: Men 2.3 mg/day, Women 1.8 mg/day. UL (Upper Limit): 11 mg/day for adults. Most multivitamins provide 1-4 mg. Dietary intake typically exceeds AI. Supplementation rarely needed. Excess more concerning than deficiency.

Manganese supplements come as gluconate, sulfate, and citrate salts. Bioavailability varies but all forms are absorbed. Amino acid chelates may have better absorption. Most multivitamins provide adequate amounts.