Nutrition
How much B12 should vegans take?
Short answer
Recognised regimens for adults: at least 10 µg a day or 2000 µg once a week (The Vegan Society); Poland’s National Centre for Nutrition Education gives 25–250 µg a day or 1000 µg twice a week. If you have a diagnosed deficiency, the doctor sets the dose.
The most common form, cyanocobalamin, is cheap, stable and the best studied. The less often you take B12, the higher the dose has to be, because only a small percentage of a large dose is absorbed.
For checking status, holotranscobalamin (active B12), methylmalonic acid (MMA) or homocysteine are better than serum B12 alone – seaweed can inflate B12 results and folic acid can mask deficiency in a blood count. Absorption of B12 from food falls with age, so supplements matter even more.
If you have symptoms of deficiency (tingling, numbness, fatigue, memory problems), see a doctor – do not raise the dose on your own.