What does vitamin B12 do for your body?


With the increasing opportunities brought by the internet, so is the trouble of finding trusted and accurate health information. When you search for causes of tiredness (fatigue), weakness, and listlessness, you will receive a bunch of websites telling us that our vitamin B12 is low. You need to replenish it with a vitamin B12 supplement. Can tiredness be caused by other things? How can you tell if they are trying to deceive you? Do you even know what vitamin B12 does for your body?

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What you need to know

Yes, to the first question. Vitamin B12 deficiency is one of the big reasons (etiologies) of fatigue, tiredness, and so on.

There are also other serious causes such as hypothyroidism, anemia, depression, and the list go on and on.

If these severe causes are not addressed promptly could be devastating.

When people go to their doctor for issues like tiredness, fatigue, weakness, and weight gain, the physician usually asks a patient couple of questions, does lab tests to rule out common, easily treated, and less expensive causes.

Additionally, life-threatening causes, if missed, can become irreversible and lead to malpractice suits. That being said, what does vitamin B12 really do for your body?

My goal today is to provide you with accurate information that will enable you to make informed choices about vitamin B12.

In this new age, everybody, irrespective of their educational or career background, seems to be an expert in health and fitness, especially giving treatment and supplement advice.

If it’s as simple as doing Google search, collecting information from various websites, and providing recommendations for people health problems, there will be no need for people becoming either a scientist or medical doctor.

This post contains affiliate links. What this means is if you purchase any product by clicking a link, my website will collect a small commission WITHOUT ANY ADDITIONAL COST TO YOU. Please, for more details, see my Affiliate Disclosures.

Vitamin B12 (cyanocobalamin): Why is it so vital?

Generally speaking, the “B vitamins” provide your entire body with a variety of essential functions, including maintaining your immune system, nervous system (the brain), blood cells, healthy skin, and helping to convert your food into energy. Studies have demonstrated that in the United States, most people, particularly the elderly, don’t meet the Recommended Dietary Allowance (RDAs) for vitamin B6 (Pyridoxine), B9 (folic acid), and B12(cyanocobalamin).

Vitamin B12 is one of the micronutrients your body requires for proper brain, immune, blood cells, skin functions, including other chemical reactions within your organization.

Vitamin B12 is basically a micronutrient that helps keep the body’s blood cells and
nerve health, and also helps to synthesize DNA, the genetic code in all cells. Additionally, Vitamin B12 helps prevent a type of anemia called megaloblastic anemia that makes people fatigue (tired) and weak.

Statistically, nearly 6 percent of the older population from 60 and above are vitamin B12 deficient, and close to 20% (1-in-5 people) is borderline deficient.

The truth of the issue is that, as you age, it is frequently harder to absorb enough B12 from food. This issue is due to a decrease in acid production in your stomach. The acid helps free B12 from our diet. Another potential cause of low vitamin B12 is the chronic use of excessive Proton Pump Inhibitor (PPI)-popularly known as Prilosec.

Some people recently had weight loss surgery (Gastric bypass)-Loss of their IF or ileal region of the small intestine.

If you are among the above groups, don’t worry you can still maintain your vitamin B12 level by either consuming fortified food or taking supplements because the acid in your stomach isn’t required for your body to absorb B12 from supplements or fortified foods.

How does your body use vitamin B12 (Physiology)?

Vitamin B12 is absorbed from the particular food you eat. This process involves two key phases.

  1. 1. The acid (hydrochloric acid) and pepsin (an enzyme) in your stomach (gastrointestinal tract) help remove vitamin B12 from the attached protein in food.
  2. 2. Vitamin B12 then rapidly binds by another protein which transports it to the small intestine.
  3. 3. The pancreatic enzymes digest the protein, which another protective protein (called intrinsic factor [IF]) in the lower part of the stomach attached to form B12-IF.
  4. 4. Once they reached the lower small intestine (ileum), B12 is absorbed by the body by IF sitting at the receptors present in the ileum.

This is the reason people with pernicious anemia (cannot make intrinsic factor) having difficulty absorbing dietary source of vitamin B12 and nutritional supplement.

What are the sources of vitamin B12?

Naturally, only in animal foods like eggs, fish, meat (beef liver), poultry, clams, and milk can people obtain a rich source of B12.

It can also be obtained in a synthetic form from the majority of fortified cereals. If you are a 100% vegan (those who don’t eat any animal-based food), you don’t have to worry about being low in vitamin B12 because you can either get vitamins from fortified food or supplements.

How much vitamin B12 you really need?

The daily amount of vitamin B12 you need is dependent on various factors:

  • Age
  • Types of diets you are eating e.g., Strict vegan diet
  • Certain medical conditions such as Crohn’s disease, pernicious anemia, celiac disease, etc.
  • Medications you are taking

Below are the average daily recommended amounts for different ages in microgram (mcg):Note: The Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 mcg.

What can vitamin B12 deficiency lead to?

B12 pernicious anemia

Pernicious anemia (PA). A blood problem in which the bone marrow produces red blood cells that are smaller than usual and larger. People suffering from PA experience symptoms fatigue, shortness of breath, headaches, and yellowish skin. Also standard are trouble keeping balance and paresthesia (numbness or tingling) of the hands and feet.

Other severe symptoms such as depression, confusion, and memory loss (amnesia) might occasionally mimic Alzheimer’s disease leading to the wrong diagnosis.

PA is typically treated with monthly injections of B12.

Heart disease. Most people with high homocysteine levels are deficient in vitamins folic acid, B12, and B6. Several studies since the mid-1980 have linked high blood levels of homocysteine (an amino acid linked with inflammation of blood vessels of the heart and brain) to increased risk of heart disease.

According to two long-term RCT studies using people at high risk for or with established cardiovascular disease, within a week, the level of homocysteine can be decreased by giving supplements containing these three B vitamins.

Nevertheless, this intervention had no effect on the number of heart attacks (myocardial infarction) or mortality (deaths) from heart disease- “the Heart Outcomes Prevention Evaluation–2 (HOPE-2) study and the Women’s Antioxidant and Folic Acid Cardiovascular Study (WAFACS).

Summary: If you are taking these vitamins to reduce the risks or prevent cardiovascular diseases, you should Stop because they are not valid. They only decrease homocysteine levels (independent heart disease or stroke risk factor).

Cancer When it comes to cancer, it’s very complex to prove if there is a link between cancer and B vitamins, especially folic acid.  According to research findings, individuals using more folic acid (folate) regularly are less likely to get colon cancer compared to those who are not. Also, studies have shown that people with a low folic acid level in their blood are more prone to disease.

Other studies suggest that people, particularly women who drink alcohol and have a low blood level folate levels, can lower their risk of getting breast cancer by consuming a more massive amount of folic acid.

Warning: although sufficient amounts of folic acid appear to suppress the formation and spread of early tumors, the excess amounts may accelerate existing tumors’ growth.

Numerous studies indicate that excess folic acid may raise the risk of colon, breast, and prostate cancer. There has been evidence that folic acid supplements increased the recurrence of adenomatous polyps, which can turn into colon cancer.

Despite all this evidence, researchers still believed that this increased cancer in the colon might be explained due to improvement in colon screening from colonoscopy.

Memory problems (Amnesia)According to research, the blood level of vitamins B6, B12, and folic acid is associated with people’s performance on tests of memory and abstract thinking.

For instance, there was a study that 112 out of 816 people (approx. 14%) developed dementia, including 70 diagnosed with Alzheimer’s disease. While individuals who started with higher doses of folic acid were less likely to have suffered cognitive regression. Some small randomized controlled trials suggest that treatment with folate and other B vitamin supplements may slow cognitive decline in older people, possibly by reducing the level of homocysteine using vitamin B6 and B12, as mentioned above in Heart disease.

Unfortunately, vitamin B supplements didn’t slow cognitive decline among those with mild to moderate dementia (Alzheimer’s disease) who took a high dose of vitamin B supplements.

Also, there was a lack of evidence to prove that the three vitamin Bs can protect healthy older people’s thinking skills or slow age-related cognitive decline, according to three studies reviewed (Cochrane Collaboration, an international group of independent experts).

Vit. B12 deficiency and vision?

Age Macular degeneration (AMD) is an eye disorder that mainly leads to central vision loss (blindness).  A 2015 study showed that people with AMD, also have high homocysteine and low vitamin B12. And the researchers believed that there is a link since other studies have demonstrated adequate vitamin B12 reduces the level of homocysteine.

Therefore, having adequate levels of vitamin B12 may help avoid the risk of age-associated macular degeneration.

Vitamin B12 and bone health/osteoporosis?

It can support your bone health and help prevent bone breakdown (what is known as osteoporosis). According to a study, over 2,500 people (adults) with a low blood level of vitamin B12 deficiency also had below-normal bone mineral density levels (Tucker et al, 2005).

Other researches have also shown an association between people, mostly women with low vitamin B12 levels and poor bone health and osteoporosis, especially.

These people with increased risk of osteoporosis are prone to bone fracture.

Take-home point: Vitamin B12 may play an essential function in maintaining your bone health. Studies have shown that people who have an increased risk of osteoporosis also have low vitamin B12 blood levels.

According to the “B bonanza: Boon or bust?”, most nutrition bars and energy drinks contain extremely high doses of B vitamins. For instance, a Red Bull container has 250% of the Daily Value* (DV) for vitamin B6. And a single 2-ounce bottled of 5-Hour Energy includes a whopping 8,333% of the DV for vitamin B12 and 2,000% of the DV for vitamin B6-and the label even suggests you can drink two bottles per day. Various bottled water brands, such as Vitamin Water, contain up to four B vitamins in amounts approaching 100% of the DV.

And you can’t necessarily trust the labels. According to Consummerlab.com,  one brand of vitamin water the agency tested contained 15 times its claimed amount of folic acid.

Note: Most of the time, manufacturers of supplements add extra in packaged products because vitamins degrade over time, but not typically that massive amount.

These megadoses provide zero benefit to your body functions, and the extra is eliminated from your body as urine because due to B vitamins water-solubility nature (“you piss out money away!”).

What happens when you take an extra dose of B12?

People who continuously take high dose experience the following side effects:

  • Headache
  • Dizziness
  • Nausea
  • Vomiting
  • Anxiety

What type of vitamin B12 dietary supplements are available?

You can find vitamin B12 in nearly all multivitamins. There are some dietary (passes through the mouth) supplements that comprise of the B vitamins (B6, B12, folic acids), and other content only vitamin B12.  This is why it’s essential to check the packaged label.

Other forms of vitamin B12 include sublingual forms (dissolved underneath your tongue). This form of B12 has not been proven to have better absorption property than pills.

Vitamin B12 can also be taken intravenously (IV), especially for people suffering from pernicious anemia or low (deficient) in vitamin B12. This form is mostly prescribed by a medical doctor.

Lastly, you have the prescription nasal gel (sprayed into the nose) vitamin B12.

According to ConsumerLab.com research, among all the vitamin B12 supplements they tested, only B-complexes contained the recommended amount (2.4 mcg). The only two recommended with the least amount but still above the RDA for deficient people are Mason Natural B12 50mcg AND a liquid form is known as Pure Encapsulation B12 (take just 1 drop)

What’s the impact of not getting enough vitamin B12?

People with vitamin B12 deficiency experiences the following symptoms and signs:

  • Tiredness (fatigue)
  • weight loss
  • weakness
  • constipation
  • loss of appetite
  • numbness and tingling (paresthesia) tingling in the hands and feet could also happen. This is medically known as peripheral neuropathy.
  • Pallor, failure to thrive, movement difficulty, and developmental delay are signs of infants’ experience.

Note:  Other diseases such as depression, hypothyroidism, anemia, and others can also make people have similar symptoms, including problems with balance (ataxia), confusion, depression, amnesia (memory loss), and soreness of the tongue or mouth (glossitis).

Because of the complication in identifying the actual cause of symptoms alone, I will recommend that you visit your healthcare provider to request that you get a comprehensive workup (blood test) if she or he ignores or prematurely diagnose your symptoms are caused by low vitamin B12.

Don’t just start popping vitamin pills, especially from a Non-Trusted Source.

Also, it is vital to consult with your doctor is because the consumption of a large amount of folate can silent the symptoms of vitamin B12 deficiency by fixing megaloblastic anemia (large red blood cells), a “hallmark of vitamin B12 deficiency. Except for the progressive nerve damages due to vitamin B12 deficiency.

This is why any healthy adults should not take more than 1,000 mcg of folic acid per day.

Energy and athletic performance

Please don’t fall for all the advertisement promotion that vitamin B12 supplements help increase your energy level and endurance during exercise. This is not true (no scientific evidence) for healthy people except in people with a vitamin B12 deficiency, as I mentioned above.

Examples of medications that interact with vitamin B12

  • Chloramphenicol (Chloromycetin®), an antibiotic (treat bacterial infections) decreases B12 level.
  • -Proton Pump Inhibitors (omeprazole [Prilosec®] and lansoprazole [Prevacid®]) used for treating heartburn [acid reflux] and peptic ulcer disease can decrease vitamin B12 level.
  • -H2 (histamine) receptor blockers (cimetidine [Tagamet®], famotidine (Pepcid®], and ranitidine (Zantac®]) for treating heartburn and peptic ulcer disease.
  • -Diabetic treatment such as Metformin ( Glucophage, Fortamet, Glumetza).
  • -Aminosalicylic acid (treat digestive problems) low B12 levels.
  • -Colchicine (Colcrys, Mitigare)-anti-inflammatory drug for treatment or prevention of gout attacks.
  • -Vitamin C (ascorbic acid) supplements-combine
    with vitamin B-12. To prevent this interaction, take vitamin B12 at least two hours before you take vitamin C.

Caution: Make sure you inform your healthcare providers and pharmacist about any medication and dietary supplements you take. They can tell you if there is an interaction between your medical prescription and dietary supplements in terms of absorption, digestion, and utilization.

Final thought and Treatment Recommendations

Now you know that not everyone needs vitamin B12 and the other B supplements. For those who are deficient of vitamin Bs particularly B12 (mostly the elderly), and people are on a strict Vegan diet, can either obtain their vitamin B12 from fortified cereal or vitamin supplements.

These are the recommendations from the Harvard Health team of researchers and medical doctors:

For most folks, the best source of RDA-appropriate levels of B vitamins is to have an optimum balanced diet, combined with a multivitamin-multimineral supplement as needed.  For those who have other general issues about an overall healthy diet. Be cautious of bars and energy drinks that may contain excess B vitamins than needed.

Avoid supplements that contain more than the RDA for this vitamin B6. Because excess amounts can cause nerve damage. Supplements promoters tend to push the idea that these are water-soluble and easily excreted. Yes, it is true, eventually be excreted, but the damaging threshold differs from one person to the next, and before excretion does occur, the damage might already be done.

Folic acid: Be careful of getting excessive amounts of folic acid from fortified foods and supplements. Most multivitamins contain 400 mcg, but many fortified breakfast bowls of cereal also contain that much. Don’t forget that other food also contains folic acids (FA). For example, products like the enriched grain; there is 172 mcg of FA in 10 pretzels and a cup of spaghetti has 166 mcg FA. By the time you finished eating all these foods, you’re over your daily threshold. Seriously, if you take the multivitamin supplements on a daily basis, avoid foods fortified with 300 to 400 mcg of folate.

Vitamin B12: This is more for elderly people (who may have a problem absorbing vitamin B12 from food) and Vegans (who don’t eat all animal-based foods) should consider taking a supplement or consuming a vitamin B12–fortified breakfast cereal.

If you decided to combine your diet with fortified cereals and vitamin supplements, please check out my Top recommendations based on researched evidence.

Truly appreciate your visiting and I hope you find it informative and enjoyable this post just as I did when writing it. What concerns or questions, even a suggestion, please leave them below and I will be more than happy to respond back within 24 hours.

This information was obtained from various sources such as Harvard Health Publication, Mayo Clinic, National Institute of Health, and Healthline. For further inquiries, the links are listed below.


This is an informational post only and should not be a substitute for your physician’s advice. If you have any questions about or use of dietary supplements and what may be best for your overall health, please talk to your medical professionals.


Tucker, K. L., Hannan, M. T., Qiao, N., Jacques, P. F., Selhub, J., Cupples, L. A., & Kiel, D. P. (2005). Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Research. Journal of bone and mineral Study: the official journal of the American Society for Bone and Mineral Research, 20(1), 152–158. https://doi.org/10.1359/JBMR.041018


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  1. I find this article a great source of information.

    Strange that the wife has just started taking vitamin B-12 for the symptoms listed in this article and here I find myself reading all about B-12.

    The older the body gets the less of many vitamins does it produce and therefore using supplements to help is more the rage nowadays.

    Obviously this is down to the internet which gets the word out. Just think 20 years ago very few would have even heard of B-12!

    Here lies a problem where more and more businesses are coming on stream to help with demand, so it is extremely important that everybody researches thoroughly the products first.

    Thank you for sharing

  2. Thanks for this post on vitamin B12. I am went vegan a few months ago, but I still ate fish because I wanted to get this vitamin naturally. But now I have decided to cut that off too for at least 3 months. Do you think that I can be without it for 3 months or should I take a supplement?

    • Hi Delyana,
      I’m glad you ask this question. It all depends what your vitamin B12 blood level is right now, your health condition, and age.
      Normally, it takes up to 3-4 years for someone who is healthy to become deficient if they stop taking vitamin B12 source food (strict vegans). So my recommendation as a medical doctor is that if you can, get a vitamin B12 blood level test from your doctor if you can. But if you can’t and in good health, monitor for any symptoms like aI mentioned in the post.
      I hope this answer your question.


  3. Hi
    I really appreciate this very informative article. I have been struggling with vitamin B and Iron deficiency for years. At first, I just had dizzy spells and a low blood count reading. Recently it has manifested itself as numbness and pains. As a child who grew up on a farm in a farming Country where we eat what we produce, and where fresh fish is the meat of choice. I would have thought this unlikely, but such has been my faith. It always seems to me like I can only get these from supplements because it doesn’t matter how much I build myself up. If I stop using them for a few months and I start having problems again.

    I can well attest to the need for supplements in my case.

    Candy Benn.

    • Hi Candy,
      Thanks for taking the time to share your personal experience on vitamin B12 deficiency. Having symptoms of numbness and low RBC is commonly caused by low B12.
      As long as you getting your supplement from reputable sources is the key. If you do need more information on managing your condition, I will gladly assist.
      Stay healthy and safe. God bless.


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