Vitamin B12 and dementia are sometimes linked because a deficiency of this important vitamin can cause problems with memory, concentration and other neurological functions.
This can be particularly important in older adults because vitamin B12 deficiency becomes more common with age.
A deficiency does not necessarily mean that a person has dementia. In some cases, vitamin B12 deficiency can cause cognitive symptoms that may resemble dementia or make existing cognitive problems more difficult to manage.
The good news is that vitamin B12 deficiency is treatable.
However, there is an important distinction to make. Correcting a genuine vitamin B12 deficiency is very different from taking extra vitamin B12 in an attempt to treat Alzheimer’s disease or another established dementia.
Current evidence does not show that vitamin B12 supplements prevent, reverse or treat dementia in people who are not deficient.
What Is the Link Between Vitamin B12 and Dementia?
Vitamin B12, also known as cobalamin, is an essential nutrient involved in several important processes in the body.
It helps maintain healthy blood and nerve cells and is required for DNA production and normal nervous system function.
When vitamin B12 levels become too low, neurological symptoms can develop.
According to the National Institute for Health and Care Excellence (NICE), vitamin B12 deficiency can be associated with cognitive difficulties such as problems concentrating and short-term memory loss.
These symptoms can sometimes resemble those seen in early dementia.
The National Institute on Aging also includes low levels of vitamin B12 among the medical and nutritional factors that can contribute to memory problems.
This is one reason healthcare professionals may investigate vitamin levels when assessing someone with new or unexplained cognitive symptoms.
Can Vitamin B12 Deficiency Cause Memory Loss?
Yes. Vitamin B12 deficiency can contribute to memory and thinking problems.
Possible neurological and cognitive symptoms may include:
- Short-term memory problems
- Difficulty concentrating
- Confusion
- Numbness or pins and needles
- Problems with balance or walking
- Weakness or fatigue
- Mood or behavioral changes
Not everyone with vitamin B12 deficiency will experience these symptoms, and these problems can have many other causes.
Memory loss should therefore not automatically be blamed on low B12 levels.
Anyone experiencing noticeable or worsening memory loss should be assessed by a healthcare professional so that the underlying cause can be investigated.
Can Vitamin B12 Deficiency Look Like Dementia?
In some people, it can.
Doctors assessing possible dementia often look for other health conditions that could be causing or contributing to cognitive symptoms.
The National Institute on Aging notes that vitamin deficiencies and several other medical conditions can cause serious memory problems that resemble dementia.
This is clinically important because some of these underlying problems can be treated.
Vitamin B12 deficiency should therefore be considered as one possible explanation for cognitive changes, rather than assuming that memory problems are automatically caused by Alzheimer’s disease or another neurodegenerative condition.
This does not mean that all dementia is reversible with vitamin B12.
A person can also have both a vitamin B12 deficiency and an underlying dementia at the same time.
Why Is Vitamin B12 Important for the Brain?
Vitamin B12 is important for normal nervous system function.
It contributes to the maintenance of myelin, the protective covering around many nerves, and is involved in processes required for healthy nerve cells and DNA formation.
Vitamin B12 is also needed for normal red blood cell production.
When a significant deficiency continues untreated, neurological damage can develop.
This is why persistent symptoms such as memory problems, numbness, balance difficulties or unusual weakness should not simply be dismissed as normal aging.
Why Are Older Adults at Greater Risk of Vitamin B12 Deficiency?
Vitamin B12 deficiency becomes more common as people get older.
NICE estimates that deficiency affects around 5% of people aged 65 to 74 and more than 10% of people aged 75 and older.
Several factors can contribute.
Reduced Absorption of Vitamin B12
The body must absorb vitamin B12 from food through the digestive system.
Some gastrointestinal conditions can interfere with this process.
Autoimmune gastritis, for example, can prevent normal B12 absorption. Previous surgery involving the stomach or the end of the small intestine can also increase the risk of deficiency.
This means a person may consume adequate vitamin B12 but still become deficient because their body cannot absorb it properly.
Dietary Intake
Vitamin B12 occurs naturally mainly in animal-derived foods.
Sources include:
- Fish and shellfish
- Meat
- Poultry
- Eggs
- Milk and other dairy products
- Foods fortified with vitamin B12
People following vegan or some vegetarian diets may therefore have a greater risk of inadequate intake unless they regularly consume fortified foods or appropriate supplements.
Older adults who eat very little because of poor appetite, illness or difficulties preparing food may also be at risk of nutritional deficiencies.
For more information on nutrition for people living with dementia, see our guide to a healthy dementia diet.
Medications
Certain medications can contribute to vitamin B12 deficiency.
For example, NICE lists metformin, which is commonly used to treat type 2 diabetes, and proton pump inhibitors used to reduce stomach acid among medications that may increase the risk.
People should not stop prescribed medications because of this risk.
Instead, anyone concerned about B12 deficiency should discuss testing and treatment with their healthcare professional.
Gastrointestinal Conditions and Surgery
Conditions that interfere with nutrient absorption can also contribute to vitamin B12 deficiency.
These include autoimmune gastritis and, in some cases, celiac disease.
People who have undergone certain bariatric operations, gastrectomy or surgery involving the terminal ileum may also be at increased risk.
The cause of a deficiency matters because it can influence how vitamin B12 should be replaced.
How Is Vitamin B12 Deficiency Diagnosed?
A healthcare professional will consider a person’s symptoms, medical history, diet, medications and possible risk factors.
Blood testing is normally used to investigate suspected vitamin B12 deficiency.
NICE recommends either total serum B12 or active B12 as the initial test in most circumstances.
Sometimes additional testing, such as methylmalonic acid or homocysteine, may be useful when the initial result is uncertain or when particular causes of deficiency are suspected.
It is important to tell the healthcare professional about any vitamin B12 supplements already being taken.
Supplements can increase blood B12 levels and may make test results more difficult to interpret without necessarily showing whether an underlying deficiency has been fully corrected.
How Is Vitamin B12 Deficiency Treated?
Treatment depends partly on why the person has become deficient.
Some people can be treated with oral vitamin B12 replacement.
Others may require vitamin B12 injections, particularly when the body cannot absorb the vitamin properly.
NICE recommends lifelong intramuscular vitamin B12 replacement for some irreversible causes, including deficiency caused by autoimmune gastritis or following certain major gastrointestinal operations.
For dietary deficiency, oral replacement and improving dietary intake may be appropriate.
This is one reason a generic “best vitamin B12 supplement” recommendation is not suitable for everyone.
The appropriate form, dose and duration of treatment should be based on the individual’s circumstances and the cause of the deficiency.
Can Treating Vitamin B12 Deficiency Improve Memory?
Treating a confirmed deficiency is important, and symptoms related to the deficiency may improve after B12 levels are restored.
NICE advises that symptoms can begin to improve within approximately two weeks in some people, although improvement can take up to three months and some symptoms may take considerably longer to resolve.
The degree of recovery can vary.
If neurological problems have been present for a long time, complete recovery is not always guaranteed.
This is another reason suspected vitamin B12 deficiency should be assessed rather than left untreated.
However, improvement after treating deficiency should not be confused with vitamin B12 acting as a general memory-enhancing supplement.
Can Vitamin B12 Supplements Treat Dementia?
This is where the evidence surrounding vitamin B12 and dementia needs to be interpreted carefully.
Researchers have observed associations between low vitamin B12 levels, increased homocysteine and poorer cognitive function in some studies.
This led to considerable interest in whether vitamin B12 or combinations of B vitamins could slow cognitive decline.
However, randomized controlled trials have generally been disappointing.
According to the National Institutes of Health Office of Dietary Supplements, clinical trials have not shown that vitamin B12 supplementation, either alone or combined with folic acid and vitamin B6, improves cognitive function in older adults with or without dementia, mild cognitive impairment or Alzheimer’s disease.
This has remained true even when supplementation successfully lowered homocysteine levels.
What About B Vitamins and Brain Shrinkage?
Older research created considerable interest after a clinical trial involving people with mild cognitive impairment found that high-dose B vitamins were associated with a slower rate of brain atrophy.
A later Cochrane review considered this and other trials.
The review found that B-vitamin supplementation probably had little or no effect on measures such as episodic memory, executive function, processing speed or quality of life.
Evidence from one study suggesting slower brain atrophy was considered interesting enough to justify further research, particularly in people with higher homocysteine levels.
But slowing a change seen on a brain scan is not the same as demonstrating that a supplement prevents dementia or produces meaningful improvement in a person’s daily cognitive abilities.
Should People With Dementia Take Vitamin B12?
A person who has dementia and a confirmed vitamin B12 deficiency should have that deficiency appropriately treated.
The presence of dementia is not a reason to ignore a nutritional deficiency.
However, taking additional vitamin B12 solely because someone has Alzheimer’s disease or another dementia is different.
Current research does not support routinely using high-dose vitamin B12 supplements as a treatment for dementia when there is no deficiency.
Anyone considering supplements should discuss them with their doctor, particularly if they are already taking medications or have other medical conditions.
The National Institute on Aging also recommends discussing supplements with a healthcare professional rather than assuming that more of a vitamin is necessarily better.
Vitamin B12 and Dementia: The Bottom Line
The relationship between vitamin B12 and dementia is important, but it is often misunderstood.
Vitamin B12 deficiency can cause memory problems, difficulty concentrating and neurological symptoms that may sometimes resemble dementia.
Because deficiency is treatable, checking for vitamin and other medical problems can be an important part of investigating unexplained cognitive decline.
If a genuine deficiency is identified, appropriate vitamin B12 replacement can correct the deficiency and may improve symptoms caused by it.
However, there is currently no convincing evidence that taking extra vitamin B12 prevents Alzheimer’s disease, reverses established dementia or slows dementia progression in people who are not deficient.
The key is therefore not simply to take more vitamin B12.
It is to identify whether a deficiency is actually present, determine why it has developed and treat it appropriately under medical guidance.