supplement
Evidence tier: strong
Essential B vitamin for nerve health, energy metabolism, and red blood cell formation, deficiency causes fatigue, nerve damage, and anaemia
A water soluble vitamin containing cobalt (the cobalamins). It works as a cofactor for two enzymes and is required for red blood cell formation, DNA synthesis and a healthy nervous system (myelin and nerve function). Its absorption pathway is what makes it unusual: food bound B12 must be freed by stomach acid, handed to a carrier called intrinsic factor made by the stomach, and absorbed low in the small intestine. Anything that lowers stomach acid or intrinsic factor (age, acid reducing drugs, autoimmune gastritis, stomach surgery) breaks this chain. Supplements and fortified foods contain free B12 and skip the acid step, which is why they can work when food B12 does not.
STRONG, BUT ONLY FOR PREVENTING AND CORRECTING A B12 DEFICIENCY. IT DOES NOT BOOST ENERGY IN PEOPLE WHO ARE NOT DEFICIENT, AND IT MUST NEVER BE MARKETED AS AN ENERGY BOOSTER. The clear, well established use is preventing and correcting deficiency, which causes fatigue, megaloblastic anaemia and nerve symptoms such as tingling and numbness. That is real and important. The honesty comes on the popular uses, per the NIH Office of Dietary Supplements. ENERGY: only if you are deficient. NIH ODS is blunt that B12 appears to have no beneficial effect on performance in the absence of a nutritional deficit. The 'B12 for energy' idea only works if you were short of it to begin with. HEART DISEASE: no. B12 with folic acid reliably lowers homocysteine, a blood marker, but a Cochrane review of 15 studies in 71,422 people found it does not prevent heart attacks or reduce death rates in people at risk of or with cardiovascular disease. Lowering the number did not lower the risk. COGNITION: not supported in people who are not deficient, per randomised trials. Who genuinely needs it: vegans and vegetarians (B12 occurs naturally only in animal foods); older adults (between 3 and 43 percent of community dwelling older adults are deficient, often from atrophic gastritis); people on metformin (which reduces B12 absorption and serum concentrations); people on long term proton pump inhibitors or H2 blockers; people with pernicious anaemia (which usually needs medically supervised treatment, often injections, not an over the counter tablet); people after bariatric surgery or gastrectomy; and infants of vegan mothers. B12 itself is one of the genuinely safe supplements: NO tolerable upper intake level, low toxicity even at high doses, safe in pregnancy and breastfeeding, and LiverTox likelihood score E (no liver signal). The one real hazard is not from B12 at all: HIGH FOLATE OR FOLIC ACID CAN CORRECT THE ANAEMIA OF A B12 DEFICIENCY BUT NOT THE NERVE DAMAGE, so it can mask a B12 deficiency until the neurological consequences become irreversible (NIH ODS Folate fact sheet). Point suspected deficiency at a clinician and a blood test, not at a product.
The requirement is tiny: the RDA is 2.4 mcg a day for adults, 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding. There is NO tolerable upper intake level. Absorption is capacity limited (about half is absorbed at small doses but only around 2 percent at 500 mcg and 1.3 percent at 1,000 mcg), which is why prevention and treatment doses run far above the RDA: for example 250 to 500 mcg daily to prevent deficiency in vegans, or 1,000 mcg daily to treat an established deficiency. There is no evidence that absorption differs by chemical form of the supplement.
Take 500 to 1000mcg daily. Sublingual (under tongue) forms bypass absorption issues affecting many people. Methylcobalamin form preferred over cyanocobalamin for neurological support.
Onset: ~7 days
Extremely safe; water soluble with no established tolerable upper limit. Supplementation essential in vegans, vegetarians, older adults, and those on metformin or PPIs. Methylcobalamin preferred for neurological indications.
Pregnancy: safe
Breastfeeding: safe
Not a traditional botanical remedy, B12 is an essential vitamin found in animal products and some fermented foods. Deficiency was historically linked to pernicious anaemia before the vitamin was identified in the 1940s. B12 supplementation is among the most evidence supported interventions for deficiency related fatigue and neurological symptoms.
Active compounds: methylcobalamin (active form), 5-deoxyadenosylcobalamin (active form), cyanocobalamin (supplement form), hydroxocobalamin (supplement form)
Remedies using Vitamin B12 · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.