Methylmalonic Acid (MMA)

Other marker

Methylmalonic Acid

Methylmalonic Acid (MMA)

Category: Other
Unit: nmol/L

A metabolite that accumulates when vitamin B12 is insufficient at the tissue level, because B12 is a required cofactor for the enzyme that converts methylmalonyl-CoA onward. It is a sensitive functional marker of B12 status that can reveal a true deficiency even when serum B12 looks normal.

PED Notes

MMA answers a question serum B12 often cannot: is there enough B12 where the cells actually use it. Serum B12 can sit in the normal range while tissue B12 is inadequate, and in that situation MMA rises early, making it the better test for suspected functional deficiency (fatigue, tingling or numbness, balance or memory changes, unexplained macrocytosis). It complements the Vitamin B12 and Active B12 (holotranscobalamin) markers already in this knowledge base: Active B12 estimates the usable fraction, MMA shows the downstream metabolic consequence of running short. Relevant to bodybuilders because frequent B12 injections are common in the community (which normalise MMA), while strict plant-based diets and metformin use (common with GH/insulin protocols) deplete B12 and can raise MMA. Note MMA also rises with impaired kidney function, so interpret alongside renal markers.

When high

When MMA is elevated (functional B12 deficiency):

  • A raised MMA with low or low-normal B12 confirms a genuine, tissue-level B12 deficiency that warrants repletion even if serum B12 looked acceptable. Cross-check Active B12 (holotranscobalamin) and homocysteine.
  • Rule out reduced kidney function as a cause of elevated MMA before attributing it solely to B12 (check eGFR/cystatin C).

Repletion:

  • Methylcobalamin or hydroxocobalamin -- 1000mcg/day sublingual or oral for milder cases; recheck MMA and B12 after 8-12 weeks
  • B12 injections (hydroxocobalamin/cyanocobalamin) -- for symptomatic or malabsorptive deficiency; already common practice in the bodybuilding community and reliably normalise MMA
  • Address the cause: strict plant-based diet without supplementation, metformin-related malabsorption, or gastrointestinal absorption issues
  • Ensure adequate folate and B6 alongside B12 so homocysteine is also controlled

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Frequently Asked Questions

Reference Ranges

Standard Range

0 - 280 nmol/L

VitalMetrics Range

0 - 280 nmol/L

Statistics