How Vitamin B12 Benefits the Brain

How Vitamin B12 Benefits the Brain

Vitamin B12 has critical benefits for the brain and nervous system, yet many are deficient in B12 because they cannot absorb it. Learn how to remedy this.

Vitamin B12 is one of eight essential B vitamins.

It is essential for overall health, but plays an especially important role in keeping the brain and nervous system working properly.

Vitamin B12 deficiency, however, is surprisingly common, affecting nearly half of all adults.

Find out if you may be at risk for deficiency and how to effectively raise your B12 level to improve your mental health and brain function.

Benefits of Vitamin B12

Vitamin B12 plays an important role in many physiological functions and protects against a variety of health problems.

It is one of the many nutrients required for building strong bones and warding off osteoporosis. 

B12 protects against heart disease by removing the toxic amino acid homocysteine from the bloodstream. 

It may reduce the severity and frequency of allergies and asthma attacks

Vitamin B12 is essential for healthy hair, nails, and skin and is sometimes prescribed to topically treat eczema and psoriasis

It is sometimes used to relieve the pain and nerve damage of shingles. 

When taken with other B vitamins, it reduces the risk of macular degeneration, an eye disease that eventually leads to blindness. 

Mental Health Benefits of B12

But where vitamin B12 is really crucial is in keeping the brain and nervous system healthy and functioning well.

B12 is needed to form memories and to focus and concentrate.

Low B12 levels are associated with depression.

This makes sense when you consider that B12 is required for the formation of the mood-boosting neurotransmitters serotonin and dopamine. 

Vitamin B12 can alleviate some of the symptoms of schizophrenia such as apathy, social withdrawal, and emotional inexpressiveness. 

Some researchers believe that the link between B12 deficiency and dementia and psychiatric disorders is so strong that patients with these conditions should have their B12 level closely monitored for life. 

Vitamin B12 Benefits for Alzheimer’s and Dementia

Many seniors diagnosed with dementia or Alzheimer’s are, in fact, B12-deficient and can make remarkable recoveries when their low B12 levels are addressed. 

This misdiagnosis occurs because the symptoms of vitamin B12 deficiency closely mimic those of these diseases.

Both vitamin B12 injections and high doses of oral supplements have proven effective for treating people with these disorders. 

There’s exciting evidence that a cocktail of B-complex vitamins may both help prevent and be useful for treating Alzheimer’s.

A University of Oxford study found that taking vitamin B12 along with vitamins B6 and folic acid improved brain function and dramatically reduced brain shrinkage in the area of the brain most affected by Alzheimer’s.

Vitamin B12 Deficiency Symptoms

Up to 40% of American adults are believed to have below-normal levels of vitamin B12. 

This is concerning, since vitamin B12 deficiency can have serious consequences.

Deficiency symptoms include weakness, loss of appetite, constipation, numbness or tingling in the arms and legs, difficulty maintaining balance, and shortness of breath. 

Effects on the brain can manifest as: 

  • anxiety
  • brain fog
  • confusion
  • dementia
  • depression
  • disorientation
  • hallucinations
  • memory loss

If left untreated, vitamin B12 deficiency can cause numerous neurological problems, including gait abnormalities, neuropathy, neuropsychiatric manifestations, and impaired vision, taste, and smell. 

In the long term, this can ultimately lead to permanent nerve and brain damage, brain atrophy, dementia, and Alzheimer’s

Who’s at Risk for Vitamin B12 Deficiency

You are at increased risk for B12 deficiency if you:

  • are a vegetarian or vegan
  • are age 60 or over
  • take acid-suppressing drugs
  • take metformin for diabetes
  • have a chronic digestive disorder such as Crohn’s, celiac disease, or irritable bowel syndrome
  • have an eating disorder
  • have had weight loss surgery
  • have H. pylori, the bacteria that causes ulcers
  • abuse alcohol or nitrous oxide
  • are HIV-positive

You can try to raise a low B12 level in two ways — with food and with supplements.

Here’s an in-depth look at each.

Vitamin B12 Food Sources

Most people get plenty of vitamin B12 in their diets.

It’s found in animal foods of all kinds — meat, poultry, pork, fish, seafood, dairy, and eggs.

Although vitamin B12 is readily found in animal food sources, there are many factors that can interfere with its absorption, including age, medications, and gastrointestinal health.

The two best sources of B12 by far are clams and beef liver; they contain 60 times more vitamin B12 than beef and over 100 times more than eggs. 

But for those who don’t eat animal products, getting adequate B12 is a serious concern.

Plant Sources of B12: A Dangerous Myth

Almost half of lacto-ovo vegetarians and over 90% of vegans are B12-deficient

And, unfortunately, there’s a persistent dietary myth that’s causing a lot of these people real harm.

Green algae (like spirulina and chlorella), fermented soy products, and brewer’s yeast are purported to be plant sources of vitamin B12. 

But, in reality, these plant foods contain B12 analogs which are similar to, but not the same as, vitamin B12.

By binding with B12 receptors, these pseudovitamins block the intake of true B12. 

So, consuming these B12 analog-containing foods can make a B12 deficiency even worse.

The only substantial vegetable source of true vitamin B12 is the sea vegetable nori (Porphyra umbilicalis). 

Some vegetarians, and especially vegans, take brewer’s yeast or yeast-based products like Marmite or Red Star Nutritional Yeast believing them to be a good food source of B12.

But nutritional yeast does not naturally contain B12; it is fortified with B12.

This makes eating yeast no different or better than taking a supplement.

If you’re a vegan, there’s no way around it.

You need to supplement your diet with B12.

I urge you to visit or to find a wealth of evidence-based information on vitamin B12.

Malabsorption: A Hidden Cause of B12 Deficiency

Unfortunately, simply eating plenty of vitamin B12-rich foods is not always the answer since many people have problems with vitamin B12 absorption.

Here’s why …

Vitamin B12 occurs in animal foods bound to protein.

B12 gets released when hydrochloric acid and gastric protease in the stomach break this bond.

But many factors can inhibit this process.

The first is age.

An estimated 20% of adults over the age of 50 have difficulty absorbing vitamin B12 from food.

Thus, it’s recommended that all seniors should consider taking supplemental B12

Eating disorders and chronic digestive disorders also make it difficult to absorb vitamin B12 from food.

Some of the most commonly prescribed medications interfere with vitamin B12 absorption.

Proton pump inhibitors (PPIs) like Nexium, Prevacid, and Prilosec and histamine-2 receptor antagonists (H2RAs) like Pepcid, Tagamet, and Zantac are popular remedies for acid indigestion, acid reflux, GERD, heartburn, and ulcers.

These drugs are strongly linked to vitamin B12 deficiency since users of these medications lack adequate stomach acid to break down and absorb vitamin B12. 

Metformin is a very popular drug for treating type 2 diabetes.

But up to 40% of patients using metformin have low levels of B12.

Metformin users are 2 to 3 times more likely to develop peripheral neuropathy, a common form of nerve damage associated with type 2 diabetes.

Lack of Intrinsic Factor

In a very small portion of the population, vitamin B12 deficiency is caused by a lack of intrinsic factor, a protein secreted by the stomach lining that binds to vitamin B12 and enables its absorption. 

Lack of intrinsic factor can be caused by weakened stomach lining or certain autoimmune diseases.

This can lead to pernicious anemia, a decrease in red blood cells that occurs when the intestines cannot properly absorb vitamin B12.

If left untreated, it ultimately leads to serious neurological damage.

Treatment usually involves mega-doses of oral B12 or regular B12 injections.

If you suspect that you have a lack of intrinsic factor, discuss this with your doctor as soon as possible.

Choosing the Best Vitamin B12 Supplement

It’s almost always preferable to get your nutrition from food rather than supplements if possible, but vitamin B12 might be an exception.

For those with compromised digestive systems, supplemental B12 is better absorbed than B12 from food where it’s bound to protein. 

And for some, the ability to absorb vitamin B12 from dietary supplements is limited by how much intrinsic factor is present.

There are a lot of options when choosing a B12 supplement.

Besides being available in the usual tablets, capsules, and liquid drops, it is also available in sublingual tablets, sprays, or lozenges.

This latter group is marketed as being more bioavailable, but studies have not found this to be the case.

You’ll also find several forms of B12 in supplements — cyanocobalamin, methylcobalamin, and hydroxocobalamin.

There seems to be little difference in absorption or bioavailability for most people. 

However, hydroxocobalamin is recommended for anyone with the MTHFR genetic mutation.

It is also the form usually used in B12 injections for treating deficiency.

Strange but true: No plants or animals can synthesize vitamin B12. It can be made only by microorganisms like bacteria and fungi. Even synthetic vitamin B12 supplements require bacteria for production.

Vitamin B12 Supplement Dosage

The Recommended Dietary Allowance (RDA) of vitamin B12 for adults is 2.4 micrograms (mcg). 

If you’ve ever read B12 supplement labels, you’ve noticed that supplements often contain much more than this.

For example, here’s the label of one that contains a whopping 83,330% of the RDA.

How Vitamin B12 Benefits the Brain
Vitamin B12 supplements contain a lot more than the RDA.

This high number seems more reasonable once you realize that only about 2% of the B12 in supplements is absorbed

If your level is very low, your doctor may want to give you injectable vitamin B12 to increase it quickly, especially if you have pernicious anemia, permanent nerve damage, or ongoing digestive problems.

However, research has found that taking an oral supplement is as effective at raising blood levels of B12 as injections, so you may want to discuss trying mega-doses of oral B12 first. 

An intriguing alternative for overcoming malabsorption is the use of a transdermal vitamin B12 patch.

According to one study (and plenty of anecdotal evidence), the use of the B12 patch shows promise. 

Vitamin B12 supplements are considered very safe and no tolerable upper intake level (UL) has been determined.

Doses as high as 2 mg per day do not cause any side effects

Vitamin B12 Testing

If you suspect that your vitamin B12 level is low, you can try taking a supplement to see if it helps your symptoms.

If supplementation will be effective, you should notice results fairly quickly, within a week or so.

But there’s only one way to know your B12 status for sure — get tested.

This is particularly advisable if you fall into one of the at-risk groups.

You can have your doctor run a B12 test or you can order one yourself from an online lab like Personalabs.

Overhyped Benefits of Vitamin B12: Energy, Weight Loss, and Memory

Lastly, here’s a look at some supposed benefits of B12 that are more hype than reality.

Billions of dollars are spent every year on supplements and energy drinks that claim to improve memory, boost energy, or aid weight loss due, at least in part, to their vitamin B12 content.


The idea that B12 can increase energy originated from the observation that it works quite remarkably to increase energy in people who are B12-deficient.

But if you aren’t deficient, taking more won’t increase your energy level one bit.

According to the International Society of Sports Nutrition, the energy boost received from energy drinks has been clearly proven to come from caffeine and sugar — not from any other ingredients, including vitamin B12. 

Weight Loss

There’s also no credible evidence that taking extra vitamin B12 can help you lose weight

Ironically, people with B12 deficiency who are underweight often gain weight when they take supplemental B12. 

This is because B12 addresses a common symptom of deficiency — poor appetite. 


Subpar levels of B12 can definitely adversely affect memory and other cognitive functions.

If you have experienced memory loss, make sure that you’re getting adequate amounts of vitamin B12 from either your diet or supplements, or both.

But that does not make B12 a miracle memory nutrient that works for everyone.

Even mega-doses of vitamin B12 do not benefit healthy adults with normal B12 levels.

Susan B. Shurin, MD, a former director at the US National Institutes of Health, gave this testimony to Congress about vitamin B12 being marketed for enhancing energy, memory, and mood:

“Some manufacturers and distributors of dietary supplements may claim that vitamin B-12 administration will improve energy levels, memory, concentration and mood.

All of these are true when the person has vitamin B-12 deficiency and are treated with B-12.

However, there is no evidence at all that these clinical benefits occur when the vitamin is given to people who are not deficient.”

Recommended: Upgrading brain health is key to making your brain work better.

Brain supplement can help you:

  • Improve your mental clarity and focus.
  • Boost your memory and your ability to learn.
  • Increase your capacity to think critically, solve problems, and make decisions.

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