The Signs of Vitamin B12 Deficiency

Vitamin B12 is one of those quiet nutrients you rarely think about until something goes wrong. Your body uses it to keep nerves healthy, to make red blood cells that carry oxygen, and to release energy from the food you eat. Because we can only get B12 from animal foods or supplements — and because a low level often creeps up slowly — deficiency is easy to miss and easy to mistake for simply feeling run down.

What B12 does in the body

B12 plays three big roles: it helps build the protective coating around your nerves, it works alongside folate to produce healthy red blood cells, and it supports the way your cells turn food into usable energy. When levels fall, all three can be affected — which is why the symptoms can be such a mixed bag.

The common signs of B12 deficiency

Symptoms tend to build gradually and can include:

• Persistent fatigue and a general lack of energy
• Tingling or "pins and needles" in the hands or feet
• Brain fog — trouble concentrating or remembering things
• A sore, smooth or red tongue, and sometimes mouth ulcers
• Breathlessness or feeling faint (from anaemia)
• Pale or slightly yellow-tinged skin
• Low mood or irritability

Who is most at risk?

Some people are far more likely to run low on B12:

• Vegans and vegetarians, since B12 comes mainly from meat, fish, eggs and dairy
• Older adults, who absorb B12 less efficiently with age
• People taking metformin (for diabetes) or long-term acid-reducing medicines such as omeprazole
• Those with absorption problems — including pernicious anaemia (an autoimmune condition), coeliac disease, Crohn's disease, or after stomach or bowel surgery

How B12 deficiency is tested

A simple blood test measures your total vitamin B12. In some people this can look normal even when the amount your cells can actually use is low, so an active B12 test (which measures only the usable fraction) can be a more sensitive early marker. B12 is often checked alongside folate and a full blood count, because the two vitamins work together and their deficiencies overlap.

The good news: it is very treatable

Once identified, B12 deficiency is usually straightforward to put right — through dietary changes, oral supplements, or B12 injections, depending on the cause and severity. If an absorption problem such as pernicious anaemia is behind it, your doctor may recommend regular injections rather than tablets. The key is finding out why the level is low so it can be treated properly rather than just topped up.

When to get checked

If you have ongoing tiredness, tingling, brain fog or a sore tongue — or you fall into one of the higher-risk groups above — a B12 test is a sensible and inexpensive way to rule it in or out. Knowing your number takes the guesswork out of it.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic