Vitamin B2 (riboflavin) — The FAD Precursor

Riboflavin is the direct precursor to the essential coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These flavoproteins are critical for mitochondrial electron transport chain function, cellular energy production, and the metabolism of fats, carbohydrates, and proteins. FAD is an obligate cofactor for methylenetetrahydrofolate reductase (MTHFR), a key enzyme in the folate cycle that regulates homocysteine metabolism. Additionally, FAD is required by glutathione reductase to maintain the cellular pool of reduced glutathione, a primary endogenous antioxidant. In preclinical models, riboflavin depletion has been shown to activate longevity pathways such as AMPK and FOXO, though this hormetic mechanism remains unproven in humans.

Riboflavin supplementation has been extensively studied in humans, particularly for its cardiovascular benefits in specific genetic subpopulations. Multiple randomized controlled trials demonstrate that riboflavin significantly lowers homocysteine levels and blood pressure in individuals homozygous for the MTHFR 677C→T polymorphism. No published human longevity trials exist.

1.6–400 mg/day depending on indication. General supplementation typically uses 2–10 mg/day, while targeted homocysteine-lowering or migraine prophylaxis protocols use up to 400 mg/day. Best taken with food to maximize absorption.

Riboflavin is generally recognized as safe with no established upper intake level, as excess is readily excreted in urine (causing a harmless fluorescent yellow discoloration). High doses (e.g., 400 mg/day) are well tolerated but may occasionally cause mild gastrointestinal distress or polyuria. It may interfere with the absorption of certain medications like tetracycline antibiotics.

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