What is vitamin B12 deficiency?
Vitamin B12 deficiency occurs when the body does not have enough vitamin B12, a nutrient that plays several vital roles. B12 is needed to make healthy red blood cells, which carry oxygen around the body, and to keep the nervous system working properly. Because the body cannot make B12 itself, it must come from the diet — mainly from animal products such as meat, fish, eggs and dairy — or from supplements.
When B12 runs low, the body cannot make enough healthy red blood cells, which can lead to a type of anaemia, and over time the nervous system can be affected too. Deficiency usually develops gradually, so symptoms can be subtle at first and easy to attribute to other things. It is a common and very treatable condition, but because untreated deficiency can lead to nerve problems that may become long-lasting, recognising and treating it matters.
Symptoms
The symptoms of vitamin B12 deficiency develop gradually and can affect the body in several ways, reflecting B12's roles in blood and nerve health. Symptoms can include:
- •Tiredness and a lack of energy
- •Feeling weak or faint
- •Pale or slightly yellow skin
- •A sore or red tongue, and mouth ulcers
- •Pins and needles (tingling) in the hands or feet
- •Problems with balance, memory or concentration
- •Feeling low in mood
Causes
Vitamin B12 deficiency can develop either because the body cannot absorb B12 properly, or because there is not enough of it in the diet. Absorption problems are actually the most common cause. Common causes include:
- •Pernicious anaemia — an autoimmune condition that stops B12 being absorbed (a common cause)
- •A diet low in B12, particularly a vegan diet without supplements, since B12 comes mainly from animal products
- •Conditions affecting the stomach or gut that reduce absorption
- •Some medicines that can affect B12 absorption over time
- •Older age, as absorption can decline
Diagnosis and treatment
Vitamin B12 deficiency is diagnosed with a blood test that measures B12 levels, often alongside other tests to check for anaemia and to help identify the cause. Because symptoms overlap with many other conditions, testing is important to confirm the deficiency rather than assuming it. If deficiency is found, further tests may look for the underlying cause, such as pernicious anaemia.
Treatment depends on the cause and severity, and is usually very effective. Where the deficiency is due to diet, B12 supplements taken by mouth, and eating more B12-rich foods, may be enough. Where it is due to an absorption problem such as pernicious anaemia, B12 is usually given by injection, at first more frequently and then as regular maintenance injections, sometimes lifelong. It is important to treat B12 deficiency properly and to keep up with any ongoing treatment, as this corrects the anaemia and, importantly, helps prevent or limit nerve-related complications.
Who is at risk and why treatment matters
Certain groups are more likely to develop vitamin B12 deficiency. People following a vegan or strict vegetarian diet without supplementing are at risk, since B12 comes mainly from animal products. People with pernicious anaemia or conditions affecting the stomach and gut, those who have had certain gut surgery, older adults, and people on some long-term medicines are also more prone to it. Being aware of these risk factors helps with earlier recognition.
Treating B12 deficiency matters for two main reasons. First, it corrects the anaemia and the tiredness and other symptoms that come with it, restoring energy and wellbeing. Second, and importantly, prompt treatment helps prevent the neurological complications that untreated B12 deficiency can cause over time, such as problems with nerves, balance, memory and mood. While these usually improve with treatment, some nerve damage from long-standing untreated deficiency can occasionally be long-lasting, which is why it should not be ignored.
The reassuring reality is that, once diagnosed, B12 deficiency is very manageable. With appropriate treatment — whether dietary, supplements or injections — most people make a full recovery from their symptoms and can maintain healthy B12 levels long-term. If you have symptoms suggesting B12 deficiency, particularly persistent tiredness with any nerve-related symptoms like pins and needles, it is worth seeing a doctor for a simple blood test.