Molybdenum vs Selenium (Selenomethionine)

Mechanism

Molybdenum is the essential cofactor for three human enzymes: sulfite oxidase (converts toxic sulfite to sulfate — critical for sulfur amino acid metabolism), xanthine oxidase (purine catabolism to uric acid), and aldehyde oxidase (aldehyde detoxification, drug metabolism). The molybdenum cofactor (Moco) requires molybdopterin as a carrier. Sulfite oxidase is the most clinically significant — sulfite accumulation is neurotoxic. Molybdenum also plays a role in the metabolism of sulfur-containing amino acids and may support phase I/II detoxification pathways.

Standard Dosing

75-250 mcg daily

Timing

With meals. Often included in multimineral formulas.

Cycle Duration

ongoing (via multimineral)

Side Effects

• Generally very well tolerated
• Gout flares at high doses (increased uric acid production)
• Copper depletion at very high doses
• Joint pain (rare)

Contraindications

• Gout (xanthine oxidase is the uric acid-producing enzyme — molybdenum supports this enzyme)
• Copper deficiency

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Mechanism

Selenium is incorporated as selenocysteine (the 21st amino acid) into 25 selenoproteins. Key enzymes: glutathione peroxidases (GPx1-4, reduce hydrogen peroxide and lipid hydroperoxides), thioredoxin reductases (TrxR1-3, maintain cellular redox balance), iodothyronine deiodinases (DIO1-3, convert T4 to T3 and regulate thyroid hormone metabolism), selenoprotein P (selenium transport and brain antioxidant), and selenoprotein W (muscle antioxidant). Selenium is essential for thyroid function, immune defense, reproductive health, and cancer chemoprevention.

Standard Dosing

200 mcg selenomethionine daily

Timing

With meals. Can be taken any time of day.

Cycle Duration

ongoing

Side Effects

• Garlic breath/body odor (selenosis)
• GI upset
• Hair loss and nail brittleness (toxicity)
• Fatigue
• Peripheral neuropathy (chronic excess)
• Potential type 2 diabetes risk at high doses (SELECT trial observation)

Contraindications

• Selenium excess (>400 mcg/day — narrow therapeutic window)
• Non-melanoma skin cancer history (SELECT trial concern)

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