The guide / Part 13

Vitamin B12 and memory: when low levels can cause forgetfulness

By The Prolongeva Editorial Team Written from the published research cited in each article Updated October 2026

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When memory slips in your late 40s or 50s, most explanations are slow and hard to pin down. In our reading, vitamin B12 is one of the few possible causes a blood test can check; the NHS says its diagnostic blood tests include B12. That is the reason it is worth understanding before you buy anything.

What can low B12 do to memory?

Vitamin B12 comes mainly from animal foods. The NHS says a diet that includes meat, fish and dairy products usually provides enough, and that the body's stores can last two to five years.

The NHS lists problems with memory, understanding and judgement among the effects of B12 deficiency, alongside tiredness and pins and needles. It also lists mood changes that can range from mild depression to confusion and dementia.

A family-medicine review in American Family Physician (Langan & Goodbred, 2017) is more cautious. It says dementia-like illness is thought to be linked to more severe and long-lasting deficiency, although it describes the supporting evidence as poor.

In our reading, that means low B12 is a reasonable thing to rule out, not a likely explanation for every lapse. We cannot judge your case; a clinician can.

Who is at higher risk of low B12?

Langan & Goodbred list groups that may warrant screening. The NHS names a similar set of causes. Together, they include:

• Older age. The AFP review names adults over 75.
• Metformin. The AFP review names use for more than four months. It cites a multicenter randomized trial of 390 people with diabetes, in which those taking 850 mg of metformin three times daily had a higher risk of deficiency.
• Acid-reducing medicines. The AFP review names proton pump inhibitors or H2 blockers taken for more than 12 months.
• Vegan or strict vegetarian diets, without supplements or fortified foods (AFP; NHS).
• Atrophic gastritis and pernicious anaemia. The NHS says pernicious anaemia, where the immune system attacks stomach cells, is the most common cause in the UK.
• Bariatric or other stomach and bowel surgery, and bowel conditions such as Crohn's disease (AFP; NHS).

Being in one of these groups does not mean you are deficient. It means the question is worth asking your doctor or pharmacist, especially before you change or stop any medicine.

What are the symptoms?

The NHS lists extreme tiredness, pins and needles, a sore tongue, muscle weakness, problems with memory and judgement, and low mood or anxiety. The AFP review describes nerve effects from progressive loss of the nerve sheath, including numbness and loss of balance sense.

None of these is specific. Poor sleep, thyroid problems and depression can cause several of them. The NHS also notes that some people have symptoms despite normal blood levels, and others have low levels without symptoms, so only a clinician can put the picture together.

In our reading, the practical clue is the company a memory change keeps. Forgetfulness that arrives with tingling, numbness, unusual tiredness or a new medicine in the mix is worth mentioning to a doctor together, not as separate complaints.

For the wider context, see brain fog in your 40s and 50s.

How does a doctor test for it?

The NHS says deficiency can often be diagnosed from symptoms and a blood test. The tests it describes check haemoglobin, red blood cell size, B12 and folate. Further blood tests can look for pernicious anaemia.

The AFP review recommends a complete blood count and a serum B12 level. When B12 is normal or low-normal but deficiency is still suspected, it names a methylmalonic acid (MMA) test as an appropriate next step.

Does taking B12 help cognitively healthy adults?

The evidence is weak or missing. A Cochrane review of vitamin and mineral supplements in cognitively healthy adults aged 40 and over (Rutjes et al., 2018) included 28 trials across all vitamins and minerals. For B vitamins, 14 trials with 27,882 participants, mainly people in their 60s and 70s, many with a history of cardiovascular or cerebrovascular disease, it concluded that supplements probably have little or no effect on global cognition up to five years. B12 status was not what the trials selected on.

Note the scope. Those trials tested folic acid, B12, B6 or combinations, not B12 alone, in cognitively healthy adults. We found no statement in that review about people with a diagnosed deficiency.

For people who are deficient, a Cochrane review (Malouf & Areosa Sastre, 2003) looked at two trials in people with dementia and low B12. It found no statistically significant treatment effect and called the evidence insufficient. It found no trials in people without dementia, or using other definitions of deficiency. It is an old review, and it does not tell us what happens to people with milder problems.

Should you test before taking B12?

In our reading, yes. We found no source suggesting that taking B12 without a deficiency protects memory. If you suspect a problem, ask your clinician about testing before you start a supplement.

If you are in a risk group, or if memory changes are new, getting worse or noticed by others, book an appointment. Ask whether B12 should be checked, and ask your pharmacist whether your regular medicines affect it. Dose and form are decisions for your clinician, not for an article.

Low B12 is only one of many possible contributors. See normal aging vs. early dementia and midlife forgetfulness for the bigger picture. If you are weighing supplements generally, our piece on nootropic supplements for memory covers the evidence.

This article is general information, not medical advice, and cannot diagnose a vitamin deficiency or any cause of memory change. Please see a clinician before starting or changing any supplement or medicine.