What are the symptoms of low B12?
Tiredness, a sore tongue, pins and needles. They build slowly, so they’re easy to miss. And B12 results have a middle zone. Land there and you may still be low.
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What are the symptoms of low B12?
The NHS lists feeling weak or tired, shortness of breath, headaches, and a sore or red tongue, sometimes with mouth ulcers. Low B12 can also hit your nerves, with pins and needles, numbness or poor balance.
These usually come on slowly. Your body’s B12 store can last around 2 to 5 years.
Think of a savings pot you stop paying into. It lasts for years, so the dip shows up long after the change. A diet change years ago can still be the cause now.
| Where | Symptom | NHS lists it as |
|---|---|---|
| Energy | Feeling weak or tired. | B12 or folate anaemia |
| Heart and lungs | Fast breathing or shortness of breath. Palpitations (a heartbeat you can feel). | B12 or folate anaemia |
| Head | Headaches. Problems with your vision, memory, understanding and judgement. | B12 or folate anaemia |
| Mouth and gut | A sore or red tongue, sometimes with mouth ulcers. Loss of appetite, indigestion, diarrhoea. | B12 or folate anaemia |
| Nerves | Numbness, pins and needles, muscle weakness, poor balance and coordination, leaking wee or poo. | B12 nerve symptom |
| Mood | Mild depression or anxiety, through to confusion and dementia. | B12 nerve symptom |
Source: NHS
You can have some of these without anaemia (too few healthy red blood cells). A full blood count with no anaemia or large red cells doesn’t rule low B12 out, NICE says.
Other things cause the same list. NICE says the symptoms vary from person to person and often aren’t unique to low B12.
Got one of these and a cause from the next section? NICE says that’s when to offer a B12 test. Ask your GP.
What causes B12 deficiency?
In the UK, the most common cause is pernicious anaemia. Your immune system attacks the stomach cells you need to absorb B12 from food.
| Cause | Who it affects |
|---|---|
| Pernicious anaemia | More common in women around 60, people with a family history of it and people with another autoimmune condition. |
| Diet | Vegans who don’t take B12 or eat foods with B12 added (fortified). Anyone who rarely eats meat, fish or dairy. |
| Stomach and gut | Part of the stomach or the end of the small bowel removed. Many types of weight-loss surgery. Radiotherapy to the tummy or pelvis. Sometimes gut conditions such as Crohn’s or coeliac disease. |
| Medicines | Stomach acid tablets called PPIs (proton pump inhibitors), such as omeprazole, and some other acid tablets. Metformin, a diabetes medicine. Colchicine (for gout), pregabalin (for nerve pain) and some epilepsy medicines. |
| Nitrous oxide | Using it for fun (laughing gas). Gas and air, used at the dentist or in labour, can also lower B12. |
Sources: NHS; NHS: complications; NICE NG239; MHRA
How common is it? Low B12 or folate affects around 1 in 20 people aged 65 to 74, and 1 in 10 aged 75 or over.
Taking metformin? Low B12 is a common side effect, more likely at higher doses and after longer use. You can usually keep taking it while your B12 is put right, but don’t stop or change it without your prescriber.
Your GP knows which medicines affect B12 and will monitor you if needed. Never stop or change a prescribed medicine without your prescriber.
More on omeprazole and blood tests and blood tests on a vegan diet.
On one of these and have symptoms? Ask your GP about a B12 test.
What B12 level is too low?
NICE says a total B12 below 180 ng/L confirms a deficiency. Your lab may use its own limits.
Some labs report pmol/L instead. There, below 133 confirms it, 133 to 258 is the middle zone, and more than 258 means deficiency is unlikely.
- Below 180 ng/LNICE: deficiency confirmed.
- 180 up to 350 ng/LNICE: possible deficiency. The middle zone.
- Above 350 ng/LNICE: deficiency unlikely.
Source: NICE NG239
From 180 to 350 is the middle zone. NICE calls it indeterminate: possible deficiency. With symptoms, your GP may order a follow-up blood test called MMA.
No symptoms? NICE says to seek medical help if they start.
Some people in the middle zone may start B12 without waiting for that result. NICE lists anyone pregnant or breastfeeding, or who’s had certain stomach or bowel surgery.
It also lists a cause that can’t be reversed, such as an autoimmune stomach condition. So does a condition that could get worse fast and badly affect daily life, such as anaemia.
More than 350 ng/L (258 pmol/L) means deficiency is unlikely. Still unwell? NICE says to look for other causes, and to consider a repeat test if symptoms last 3 to 6 months.
Had an active B12 test? Below 25 pmol/L confirms a deficiency, and 25 to 70 is the middle zone. More than 70 pmol/L means deficiency is unlikely.
On the combined pill? NICE says it can lower total B12 without causing a deficiency, but a low result can still mean you’re low.
Already taking B12? It may raise your result without fully fixing a deficiency. Questions for your GP:
- Was my result total B12 or active B12, and what was the number?
- If I’m in the middle zone, should I have an MMA test?
- What’s causing my low B12? Do I need a test for pernicious anaemia?
- Could any of my medicines be lowering my B12?
More on the B12 blood test and high B12 levels.
How is low B12 treated?
What usually happens after a low B12 result
- 1
Find the cause
Your GP may test for pernicious anaemia or refer you.
- 2
Injections first
With anaemia, usually B12 injections every other day at first.
- 3
Then by cause
Diet: you may take daily tablets between meals, or have an injection twice a year. Pernicious anaemia: usually an injection every 2 to 3 months, for life.
- 4
Check it worked
Often a blood test 7 to 10 days in, and maybe another at about 8 weeks.
Sources: NHS: diagnosis; NHS: treatment
Low B12 from a medicine such as a PPI or metformin? NICE says tablets or injections while you take it, and a review if the medicine stops.
How long until you feel better? NICE says symptoms could start to improve within 2 weeks, but it may take up to 3 months. They may get worse at first, but NICE says this should improve.
Numbness or tingling from low B12? The NHS says you’ll be referred to a haematologist, a blood specialist, and may need injections every 2 months.
Six B12 steps you can take now
- Tell your GP about any B12 tablets, injections or patches you already use.
- Ask for the B12 blood test before you start a supplement.
- Eat B12 foods: meat, fish, milk, cheese, eggs or some fortified breakfast cereals.
- Vegan? Eat foods with B12 added (fortified) or take a B12 supplement.
- Buying B12? Pick one with cyanocobalamin, methylcobalamin or adenosylcobalamin.
- Keep bought B12 to 2mg a day or less. The NHS says that’s unlikely to cause harm.
Sources: NICE NG239; NHS: B vitamins; NHS: causes
Taking folic acid? Doses above 1mg can hide the signs of low B12. So before prescribing it, your GP checks your B12.
See B12 injections, high folate and low folate.
Can low B12 cause lasting damage?
Sometimes. Many symptoms improve with treatment, but the NHS says nerve problems can sometimes be permanent.
The longer it goes untreated, the higher the chance of permanent damage. So the NHS wants it diagnosed and treated as soon as possible.
Complications are rare, because most cases are easy to treat. In adults, severe anaemia can lead to heart failure, where the heart can’t pump enough blood around the body.
Pregnant? Low B12 can raise the risk of a neural tube defect. That’s a serious birth defect of the baby’s brain or spine.
Pregnant and think you may be low? Tell your GP or midwife, and ask whether you can use gas and air in labour.
When to speak to a GP
The NHS says to see a GP if you think you may be low. Your symptoms and a blood test often give the answer. Book an appointment if:
- You have symptoms on the NHS list and a cause from the table above, such as a vegan diet, acid tablets or stomach surgery.
- You have numbness, pins and needles, poor balance or memory problems. Nerve damage can sometimes be permanent.
- You’re pregnant or breastfeeding and think you may be low.
- Your result was in the middle zone and new symptoms start. NICE says to seek medical help.
- You’re on treatment and symptoms don’t improve, get worse, come back, or new ones start. NICE says don’t wait for your next appointment.
Tired for other reasons too? See always tired, tingling and numbness and the energy and fatigue hub.