Vitamin B12 is essential for nerve function, red blood cell formation and DNA, and it occurs naturally in meat, fish, eggs and dairy but not in plant foods in usable amounts. Because of this, anyone following a fully plant-based diet should get B12 from a supplement or consistently from fortified foods such as some plant milks, cereals and nutritional yeast.
Deficiency can develop slowly and may cause fatigue, tingling or numbness, balance problems, memory issues, mouth soreness and anaemia. Nerve damage from prolonged deficiency can become permanent, so prevention matters and this is not an area to leave to chance.
Vegetarians who eat little dairy or egg, older adults, people on certain medicines such as metformin or long-term acid-reducers, and those with absorption problems are also at risk. A doctor or pharmacist can advise on dosing and whether a blood test is worthwhile.