Oral vitamin B12 doesn't work; only injections fix a deficiency
Mostly falseThe Claim
Many people believe B12 tablets are poorly absorbed and that injections are the only real way to correct a B12 deficiency.
Origin
Injections were the historical standard of care, largely because of pernicious anaemia, in which normal intestinal absorption fails.
What Science Says
A Cochrane review of randomized trials comparing oral and intramuscular B12 found that high-dose oral B12 (1,000 µg/day) produced no clinically relevant difference in serum B12 levels versus injections, and one trial using 2,000 µg/day found higher levels with oral treatment (+680 pg/mL). Oral treatment was also cheaper. The evidence is low quality because only 3 trials (153 participants) exist, and doses much higher than daily needs are required.
Verdict
Mostly False