Vitamin B12, memory loss and dementia

Deficiency affects young and old alike.

Maria Cross MSc
Feb 2 · 7 min read

Take a look at the quote below. It’s the first line of a research paper published in 2016 that tells you that high blood levels of a substance called homocysteine is a risk factor for two common types of dementia — a risk factor that is within your control.

High homocysteine (Hcy) is an indication of low vitamin B12 status. It is also a risk factor for other serious diseases too, especially cardiovascular disease and stroke, as it can damage the walls of blood vessels. Hcy can easily be lowered. For some people, awareness of this fact could be life changing.

But have you even heard of homocysteine?

And if you think this is an issue that only concerns the elderly, think again. Young people can also experience memory loss, as a result of B12 deficiency.

In 2013, The Journal of Neuropsychiatry and Clinical Neurosciences published the case of a 27-year-old man who for six months had been experiencing behavioural changes that included delusions and “wandering tendencies”. He was diagnosed with psychosis and given anti-psychotic medication. They didn’t work, and a month later he returned, with more symptoms: aggression, incontinence, and memory problems.

A CT scan revealed some brain shrinkage (atrophy), and a blood test revealed extremely low vitamin B12. The antipsychotic medication was stopped, and instead he was given intramuscular injections of B12 — daily at first, then weekly, then monthly. Memory problems and behavioural symptoms (and urinary incontinence) were all completely resolved within a month, and he was discharged.

So what is homocysteine?

Hcy is an amino acid that is created during the metabolism of the amino acid methionine to cysteine. Ordinarily, levels are kept within certain limits. But when the system doesn’t work, levels rise.

High Hcy is implicated in brain atrophy. Particularly affected is the hippocampus, the area of the brain most closely associated with memory. The higher the Hcy, the greater the level of atrophy, as evidenced by MRI scans of elderly people.

Some brain shrinkage is normal with ageing, even in people without cognitive impairment. It’s the speed of the atrophy which is relevant, being an indication that something is amiss. (Smith et al 2010)

Normal Hcy metabolism is regulated by a trio of B vitamins: B12, folate and B6, working together as cofactors. To lower blood levels of Hcy, you just need a regular intake of these three vitamins.

Deficiency of B6 is uncommon and unlikely for most people, as this vitamin is widely distributed in food.

Folate deficiency is more common. To obtain a good supply of folate (which is called folic acid when it is provided in supplement form), you need to ensure a regular supply of leafy green vegetables, such as spinach and broccoli.

Vitamin B12 is the trickiest one, the one most likely to be missing from diet.

Most people are aware that vitamin B12 is found only in animal source foods, and that anyone who chooses to avoid these foods needs to supplement appropriately. For more details on the best form and strength of supplements, see my article The Four Stages of Vitamin B12 Deficiency.


Dietary avoidance is is not the only cause of deficiency of B12, especially for the elderly.

Large surveys in the US and UK have found that around 6% of people over the age of sixty are vitamin B12-deficient, and this percentage increases with age , rising to 10–15%.

This deficiency is attributed to high prevalence of gastric atrophy among the elderly. Gastric atrophy is a condition that arises when the lining of the stomach becomes inflamed, usually as a result of an infection caused by the bacterium Helicobacter pylori. The result is malabsorption.

Other causes of B12 deficiency include pernicious anaemia, smoking, and certain medications, especially metformin and antacids. Metformin, the drug commonly prescribed to treat type 2 diabetes, lowers vitamin B12 levels in 30% of people taking this drug over a long period of time.


In young people, however, the cause of B12 deficiency is more likely to be dietary avoidance. Vitamin B12 deficiency can cause dementia-type symptoms in young people, but symptoms are reversible, once the cause has been identified.

In the case of the 27-year-old man mentioned above, enquiries about his diet revealed “very low” intake of animal foods.

A water-soluble vitamin, B12 is crucial to the brain and nervous system. As well as memory loss, there may be delirium, depression, confusion and — rarely — schizophrenia.

.. and old

The problem for older people is that symptoms of dementia may not be recognised as a B12 deficiency. There is no cure for Alzheimer’s disease and other forms of dementia, but B12 deficiency can be corrected. It’s just a question of making the right diagnosis, and in good time.

In 2019, scientists reported the case of a 68-year-old woman experiencing memory problems and confusion. So bad were her symptoms that there were times when she could not identify family members. Although her folate levels were normal, B12 was low and she had high homocysteine. She had no history of psychiatric ill-health, or of taking medications or drugs that might cause psychiatric side effects.

After high-dose, intravenous B12 treatment, the patient experienced a “dramatic improvement” in her symptoms. She was told to take 500mg of oral B12 three times a day indefinitely. Two months later:

Studies have shown that high-dose vitamin B supplements can significantly slow down the rate of cognitive decline. Of a group of 168 people with mild cognitive impairment (the pre-dementia stage), half were given B12, folic acid, and B6 and the other half received a placebo, for a period of two years.

At the end of the trial, the B vitamin group were found to have 53% lower Hcy than the placebo group. They also scored significantly better in memory and cognitive function tests. Those given a placebo, on the other hand, experienced a significant increase in Hcy levels over the 2-year period.

The researchers concluded that:

“The accelerated rate of brain atrophy in elderly with mild cognitive impairment can be slowed by treatment with homocysteine-lowering B vitamins.” (Smith et al 2010)

Although treatment with B vitamins can reduce the rate of brain shrinkage in people with elevated Hcy, treatment appears to be effective only before dementia takes hold, that is, at the mild cognitive impairment stage.

Take action

But why wait until you develop mild cognitive impairment? Dietary modifications that ensure a consistent and plentiful supply of B vitamins are easy to implement, and should form a life-long habit. If you avoid animal source foods, be sure you supplement appropriately, and also test for homocysteine. This is a straightforward test you can do at home. Below is a sample report (from York Laboratories, in the UK).

Why the big secret?

It is scandalous that the role of homocysteine and B vitamins in disease, especially dementia and cardiovascular disease, is so little known. It may be a scandal, but it is not a surprise: there are no drugs that can lower excessive Hcy — just B vitamins, vitamins that can’t be patented and are cheap to buy over the counter.

As ever, you just have to follow the money. In this case, there isn’t any.

Scottish doctor and author, Malcolm Kendrick, rightly calls this absence of medical interest a “deafening silence”.

Last word

There is hope. In 2018 the Journal of Alzheimer’s Disease published a Consensus Statement, which was the conclusion of a panel of experts who examined all the relevant research. They state:

The researchers state that screening for raised total Tcy should be carried out in memory clinics, and people found to have high levels should be offered supplementary B vitamins. Apparently, this is something that already happens in Sweden.

Let’s hope the rest of the world catches up soon.

Feed Your Brain

Feed Your Brain explores the link between diet and mental…

Maria Cross MSc

Written by

Nutritionist and nutrition science writer, specialising in diet and mental health. Subscribe to for free brain food guide. @MariaXCross

Feed Your Brain

Feed Your Brain explores the link between diet and mental health, and how food influences brain function. How what you eat — or don’t eat — can change the way you feel, and even affect your ability to learn new things, remember past events and sharpen your focus.

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