B12 Shortfall Disrupts Mitochondrial DNA Integrity in Muscle Cell Models

The team cultured primary myoblasts from donors aged 25-35 and induced B12 depletion via media lacking cobalamin plus transcobalamin-blocking antibodies for 14 days. They quantified mtDNA copy number by qPCR, measured complex I and IV activity with spectrophotometry, and tracked oxygen consumption rates on a Seahorse analyzer. Low B12 raised 8-oxoguanine lesions in mtDNA and halved spare respiratory capacity compared with B12-replete controls.

These cellular changes mirror fatigue and sarcopenia patterns seen in older adults with serum B12 below 200 pmol/L. The mitochondrial enzyme methylmalonyl-CoA mutase requires B12; its dysfunction accumulates odd-chain fatty acids that damage mtDNA polymerase gamma. Prior human cohort data from the Framingham Offspring Study already linked low B12 to poorer grip strength, yet lacked direct mechanistic evidence.

A parallel aged-mouse experiment supplemented 18-month-old females with 10 micrograms per kilogram B12 for eight weeks, restoring mtDNA integrity markers but not fully reversing muscle mass loss. The design used littermate controls and blinded histology, yet relied on supraphysiological dosing.

Next steps include a 12-month randomized trial of 500 micrograms oral methylcobalamin versus placebo in 300 adults over 70 with baseline B12 150-250 pmol/L, measuring change in 6-minute walk distance and muscle biopsy mtDNA mutations.