Vitamin B12 Deficiency: Symptoms, Blood Tests and Treatment
Vitamin B12 is a nutrient your body needs to make healthy red blood cells, keep your nervous system working properly, and produce DNA. When levels run low, it can affect energy, mood, memory and physical health in ways that are easy to mistake for something else.
This guide gives you a clear overview: what B12 deficiency is, who’s more likely to get it, the symptoms to look out for, how it’s tested, and the treatment options available. Where a topic deserves more depth, we’ve linked to a dedicated guide.
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What is Vitamin B12 deficiency?
Why Does B12 Deficiency Happen?
Dietary Factors
B12 is mainly found in animal products (meat, fish, eggs, dairy). Vegans and strict vegetarians are at a higher risk without supplementation.
Absorption Issues
Digestive conditions, medications, or autoimmune issues like pernicious anaemia can block your body from absorbing B12 properly.
Increased Need
Pregnancy, aging, or underlying long-term health conditions can significantly raise the amount of B12 your body requires.
Who is more at risk?
Risk Factor Checklist — Do Any Apply to You?
Follow a vegan or strict vegetarian diet
Are over 65 years of age
Have a digestive condition affecting absorption (e.g. Crohn’s or coeliac disease)
Have had weight-loss (bariatric) surgery
Take certain long-term medications (including acid reflux or diabetes drugs)
Have an autoimmune condition such as pernicious anaemia
Are currently pregnant or breastfeeding
This isn’t a complete list, and being in one of these groups doesn’t automatically mean you’re deficient — it simply means it may be worth checking.
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Common symptoms of Vitamin B12 deficiency
Symptoms can develop slowly, which is part of why they’re often missed or blamed on something else. They can include:
Common Symptoms of Vitamin B12 Deficiency
Energy & Body
- • Ongoing tiredness or low energy
- • Pale or slightly yellowish skin
- • A sore or unusually smooth tongue
- • Mouth ulcers
Sensation & Mobility
- • Pins and needles in hands or feet
- • Changes in the way you walk or move
- • Disturbed vision
Mood & Memory
- • Irritability or low mood
- • Difficulty with memory or focus
- • Trouble with understanding or judgement
These symptoms have many possible causes beyond B12 deficiency, which is exactly why testing rather than guessing matters.
Why is testing important?
Because B12 deficiency symptoms overlap with so many other conditions (thyroid problems, iron deficiency, and general fatigue from stress or poor sleep, to name a few), a blood test is the only reliable way to confirm whether low B12 is actually the cause.
Key Reasons to Get Tested
Avoid Misdiagnosis: Treating the wrong condition can delay finding the true source of your symptoms.
Custom Long-Term Plans: Underlying causes like pernicious anaemia require dedicated management, not a quick fix.
Appropriate Interventions: B12 injections aren’t universally effective for every case of fatigue.
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Testing usually involves a simple blood sample, which is sent for analysis to measure your B12 level. Depending on your symptoms and history, a clinician may also check related markers, such as folate, iron, or a full blood count, to build a clearer picture.
Some people ask whether they need a blood test before having a B12 injection. In most cases, yes — a test helps confirm whether an injection is actually appropriate for you, rather than starting treatment blind.
Treatment options for Vitamin B12 deficiency
Tailored Treatment Pathways
Treatment depends on cause and severity. Select a pathway below:
Pathway 01
Dietary Adjustments
Increasing B12-rich foods is often sufficient for mild cases, sometimes supported by low-dose oral supplements.
Pathway 02
Oral Supplementation
Daily or weekly tablets effectively help maintain optimal B12 levels when gut absorption functions properly.
Pathway 03
B12 Injections
For significant deficits or conditions like pernicious anaemia, injections completely bypass the digestive system for direct delivery.
Treatment should always be guided by test results and a clinician’s assessment — not chosen based on symptoms alone.
When should you speak to a pharmacist or GP?
It’s worth getting checked if you have ongoing, unexplained tiredness, tingling or numbness, mouth soreness, low mood, or memory difficulties — especially if you fall into one of the higher-risk groups above.
Seek prompt medical advice if you experience sudden vision changes, significant difficulty walking, or a rapid change in mental clarity, as these can occasionally indicate a more advanced deficiency that needs urgent attention.
Got Questions? We Have Answers.
Can Vitamin B12 deficiency be cured?
Many causes can be effectively managed once identified — through diet, supplements, or injections — though some underlying causes, like pernicious anaemia, need ongoing, lifelong treatment rather than a one-off fix.
How quickly will I feel better after treatment?
This varies from person to person and depends on how low your levels were and the underlying cause. Some people notice an improvement in energy within days to weeks, though some symptoms take longer to resolve.
Can I just take a B12 supplement without testing first?
You can, but if your fatigue or other symptoms aren’t actually caused by B12 deficiency, a supplement won’t fix them — and it may delay finding out what’s really going on. Testing first gives you a clearer answer.
Is a B12 deficiency serious?
Mild deficiency is common and usually straightforward to treat. Left unaddressed for a long time, more significant deficiency can affect the nervous system, which is why earlier testing and treatment are better than waiting.
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