Vitamin B12 deficiency is insidious: it develops slowly and the symptoms are often vague. Yet a long-term shortage can have serious consequences for your nervous system and blood cell production. This article is part of our overview of vitamin deficiency. Below you read who is at risk and how to detect a shortage.
What B12 does
Vitamin B12 (cobalamin) is essential for:
- Red blood cell production (prevents anaemia)
- Nervous system function (protects the myelin sheath)
- DNA synthesis and cell division
- Energy production in your cells
- Neurotransmitter production (influences mood and cognition)
Vitamin B12 deficiency symptoms
The symptoms usually develop gradually. Common complaints are fatigue, tingling in hands and feet and concentration problems. The combination of fatigue with tingling fits B12 better than fatigue alone, which can also belong to a vitamin D deficiency.
- Fatigue and weakness - from reduced red blood cell production
- Tingling or numbness - in hands and feet (nerve damage)
- Concentration problems - difficulty focusing, forgetfulness
- Low mood or irritability
- Balance problems - from damage to the nervous system
- Sore, red tongue (glossitis)
- Pale or yellowish skin
Nerve damage from a prolonged B12 deficiency can be irreversible. Early detection therefore matters.
Normal values
- Above 300 pmol/L - normal
- 150 to 300 pmol/L - grey area (possible functional deficiency)
- Below 150 pmol/L - deficient
For values in the grey area, an additional test for methylmalonic acid (MMA) or homocysteine can clarify a functional deficiency.
Who is at risk of a vitamin B12 deficiency?
- Vegetarians and vegans - B12 occurs almost exclusively in animal products
- Older adults (65+) - absorption of B12 from food declines with age
- People with gut conditions - coeliac disease, Crohn's, stomach surgery
- Long-term acid reflux medication users - PPIs reduce B12 absorption
- Metformin users - this diabetes medicine can reduce B12 absorption
- People with pernicious anaemia - an autoimmune condition that blocks B12 absorption
Correcting a vitamin B12 deficiency
With a confirmed deficiency the approach depends on the cause and severity. Mild deficiencies are often covered by oral supplements, while absorption problems or severe deficiencies may need injections prescribed by your doctor. Discuss the right form and dose with your GP. Read more about correcting vitamin B12 with tablets or injections.
Frequently asked questions
How long to correct a deficiency?
Blood values often improve within 6 to 8 weeks. Nerve symptoms may take months and may not fully reverse if the deficiency was prolonged.
Can I take too much vitamin B12?
Vitamin B12 is water-soluble: an excess is excreted through your urine. Toxicity from supplements is barely described. Even so, it is wise to supplement based on a confirmed deficiency.
Do I need to fast for a B12 test?
No, fasting is not needed. Always mention if you take B12 supplements, as this affects the result.
Want to measure your vitamin B12? Check your vitamin B12 value or build a custom blood test. Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss symptoms and treatment decisions with your GP.
References
- Thuisarts.nl / NHG. Vitamin B12: what if you have too little? Accessed 2026.
- Health Council of the Netherlands. Dietary reference values for vitamins and minerals. 2018.
- Netherlands Nutrition Centre. Vitamin B12. Accessed 2026.
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