Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| Biotin (B7) | Methylcobalamin (B12) | |
|---|---|---|
| Category | Vitamins | Vitamins |
| Standard Dose | 2500-5000 mcg daily | 1000-5000 mcg methylcobalamin daily (sublingual preferred) |
| Timing | With meals. Any time of day. | Morning, sublingual for best absorption (bypasses intrinsic factor requirement). Can combine with methylfolate. |
| Cycle Duration | ongoing for maintenance; 3-6 months for hair/nail cosmetic benefit | ongoing |
| Evidence Level | moderate_human | strong_human |
Biotin serves as a covalently bound coenzyme for five mammalian carboxylase enzymes: acetyl-CoA carboxylase (fatty acid synthesis), pyruvate carboxylase (gluconeogenesis), propionyl-CoA carboxylase (odd-chain fatty acid and amino acid metabolism), 3-methylcrotonyl-CoA carboxylase (leucine catabolism), and methylcrotonyl-CoA carboxylase. It also plays a role in histone biotinylation (epigenetic regulation), gene expression regulation, and cell signaling. Essential for keratin infrastructure in hair, skin, and nails.
2500-5000 mcg daily
With meals. Any time of day.
ongoing for maintenance; 3-6 months for hair/nail cosmetic benefit
Methylcobalamin serves as a cofactor for methionine synthase, transferring a methyl group from 5-MTHF to homocysteine to regenerate methionine and subsequently SAMe. Adenosylcobalamin (the other active B12 form) is a cofactor for methylmalonyl-CoA mutase in mitochondrial energy production and odd-chain fatty acid metabolism. B12 is essential for myelin synthesis, DNA synthesis (thymidylate synthase pathway), red blood cell maturation, and neurological function. Deficiency causes megaloblastic anemia and irreversible subacute combined degeneration of the spinal cord.
1000-5000 mcg methylcobalamin daily (sublingual preferred)
Morning, sublingual for best absorption (bypasses intrinsic factor requirement). Can combine with methylfolate.
ongoing
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