Vitamin B12 Deficiency: 10 Warning Signs, Who Is at Risk and How It’s Treated

Low vitamin B12 is one of the most commonly missed causes of tiredness. It creeps up slowly, it is easy to blame on stress or night shifts, and if it is left untreated for too long it can cause nerve damage that does not fully recover. A simple blood test can find it.

Imagine feeling exhausted for months. You sleep, but you never feel rested. Your feet tingle at night, you keep losing your train of thought, and your tongue feels oddly sore. You put it down to getting older or working too hard. Then a routine blood test shows your B12 is very low, and within weeks of treatment you start to feel like yourself again.

Why your body needs B12

Vitamin B12 helps your body make healthy red blood cells and keeps your nerves and brain working properly. Your body cannot make it, so it has to come from food or supplements. It is found naturally in meat, fish, eggs and dairy, and is added to some breakfast cereals, plant milks and nutritional yeast.

10 warning signs of low B12

1. Extreme tiredness and lack of energy
2. Breathlessness and a fast heartbeat on mild effort
3. Pins and needles or numbness in the hands and feet
4. A sore, red, smooth tongue
5. Mouth ulcers
6. Pale or slightly yellow skin
7. Problems with memory, concentration or thinking
8. Low mood, irritability or other changes in mood
9. Problems with balance or walking
10. Blurred or disturbed vision

Not everyone has all of these, and nerve symptoms can appear even before blood counts change.

Who is most at risk?

• People with pernicious anaemia, an autoimmune condition where the stomach cannot absorb B12. It is one of the most common causes in many countries.
• Vegans and some vegetarians who do not eat fortified foods or take a supplement
• Older adults, who absorb B12 less well
• People taking metformin for diabetes long term, or acid-reducing medicines such as omeprazole
• People who have had stomach or bowel surgery, including weight-loss surgery
• People with Crohn’s disease or coeliac disease
• Babies of breastfeeding mothers who are low in B12

How it’s diagnosed and treated

Diagnosis starts with blood tests: a full blood count and a B12 level. Some people need extra tests to check for pernicious anaemia or to confirm a borderline result.

• Injections are used when the body cannot absorb B12 well, or when symptoms are severe. Usually a course of several injections is given first, followed by regular top-ups, sometimes for life.
• Tablets may be enough if the cause is diet and absorption is normal.
• Diet changes: more B12-rich or fortified foods, especially for people on plant-based diets.

Many people notice more energy within days to weeks of starting treatment. Nerve symptoms can take longer to improve.

But can’t I just take a supplement and skip the test?

It’s better not to. Taking B12 before a blood test can hide the result and make it harder to find the cause. And if the real problem is pernicious anaemia, ordinary supplements may not be enough. Get tested first, then treat. Also take care with folic acid supplements on their own: they can mask the anaemia from B12 deficiency while nerve damage continues.

Sources: NHS (Vitamin B12 or folate deficiency anaemia), US National Institutes of Health Office of Dietary Supplements, World Health Organization, NICE. This guide is for general information and does not replace advice from your own nurse, doctor or pharmacist.