B12 Vitamin: Benefits, foods & side effects

Vitamin B12 is one of the most frequently studied vitamins and the first that comes to mind if someone feels exhausted or is simply a vegetarian! But what exactly is it and how necessary for the body?

What is vitamin B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that belongs to B-complex vitaminς. It is mainly found in animal foods and plays an important role:

• in the formation of red blood cells
• in cell division
• in energy metabolism
• in reducing fatigue
• to our immune health
• in the nervous system
• in DNA synthesis
• in brain function

Normal levels

According to most experts, normal levels in adults range between 190-950 pg/mL, however it is ideal when it is above 300 pg/mL. (Values may vary by laboratory or unit of measurement).

In general, deficiency is considered when it is <200 pg/mL and in this case more tests are required.

However, in some countries, such as Japan, a lower safe limit of 500 pg/mL has been set, thus preventing deficiencies and problems such as memory loss, homocysteine disorders, etc.

B12 health benefits

The most important benefits of vitamin B12 for the body are:

1. Energy production

This nutrient contributes significantly to energy production, which is why fatigue and weakness are often associated with its lack. More specifically, our body uses glucose as “fuel” and vitamin B12 contributes decisively to the conversion of carbohydrates (food) into glucose. In addition, the body uses B12 to convert fatty acids into energy. (3).

2. Brain function

Vitamin B12 appears to contribute to normal neurological and psychological functions (4). It is necessary for the proper development of the nerves, but also of the brain.

Thus, by ensuring sufficient levels of vitamin B12, we reduce the possibility of some brain dysfunction, such as dementia, memory loss, etc. (5).

3. Anemia Treatment 

Thanks to B12’s ability to participate in the formation of red blood cells, its role is decisive in the case of anemia. In fact, anemia can often be due to B12 deficiency, as in megaloblastic anemia. That is why taking it through supplements or even injections is often the primary choice of the physician for its treatment (6).

It is important to consult your doctor before taking it, as you may need to combine it with folic acid and iron.

4. Homocysteine regulation

Vitamin B12 helps lower homocysteine levels, a substance that appears to be linked to cardiovascular disease. It is even more effective if combined with folic acid and vitamin B6.

In addition, homocysteine low levels are associated with better prevention against macular degeneration, an eye condition that is quite common in the elderly as well as the middle-aged.(5)

5. Bone health

Adequate intake of vitamin B12 can support good bone health. A study of more than 2,500 adults showed that those deficient in vitamin B12 had lower-than-normal bone density—men in the hips, and women mostly in the spine (7). As a result the bones become more fragile and the risk of osteoporosis increases !

6. Prevents depression

Vitamin B12 plays an important role in the production of serotonin – also known as the happiness hormone – and other brain substances. Several studies found that people with low B12 levels were more likely to develop depression. On the contrary, increased B12 is likely to help in better treatment of the disease! (8)

7. Healthy skin

Like all B vitamins, B12 also contributes to healthy skin, hair and nails. But what has been found regarding abnormal levels of it, is that there is a correlation with skin problems, such as acne, discoloration or hyperpigmentation of the skin, vitiligo, acne or atopic dermatitis!

Close to these are the various changes and inflammations in the oral mucosa, such as aphthous stomatitis or glossitis.(9)

8. Necessary in pregnancy

Its importance is great, especially at the beginning of pregnancy, since along with folic acid they contribute to a healthy neural tube in the fetus. If a woman is deficient in this in the early stages of pregnancy, the chances of birth defects in the fetus as well as low birth weight increase (5).

The recommended daily intake in pregnancy is 2.6 mcg and in breastfeeding 2.8 mcg per day.(6) Most of the time, these doses are covered by the pregnancy or breastfeeding multivitamins that a woman usually takes.

Foods rich in B12

Basically, vitamin B12 is found in foods of animal origin, such as (1,2):

1. meat
2. poultry
3. fish and seafood
4. dairy products
5. eggs

Generally, vitamin B12 is synthesized by bacteria. Although bacteria in the human intestine can synthesize vitamin B12, this vitamin is not preserved for long and is not absorbed to a satisfactory degree, which is why it is necessary to obtain it from food.

Vitamin B12 is found in small amounts in plant foods, especially those that have been fermented, but they are not considered good sources (1).

Options such as nutritional yeast, miso and tofu (Asian cuisine), spirulina and algae continue to be considered good for vegetarians and vegans, but their needs will hardly be met with these. They will need foods fortified with vitamin B12, such as cereals and plant-based milks, as well as a dietary supplement.

Table of foods with Vitamin B12 

B12 Deficiency symptoms

The most common symptoms of vitamin B12 deficiency are (11):

1. Fatigue
2. Headache
3. Pale or yellow skin (jaundice)
4. Numbness or tingling in the extremities (hands and feet)
5. Brain disorders (blurred thinking, depression, memory loss, etc.)
6. Vision disorders
7. Muscle weakness, difficulty walking
8. Glossitis, swollen tongue, aphthae

High risk groups

Increased chances of B12 deficiency have people who (11) :

• are vegetarian or vegan
• have malabsorption syndromes (e.g. Crohn’s disease, celiac disease, parasites, etc.)
• abuse alcohol
• are being treated for heartburn, ulcers or diabetes
• have immune disorders (e.g. lupus, Graves’ disease)
• have atrophic gastritis
• suffer from pernicious anemia
• are elderly, with difficulty in feeding
• have digestive disorders (usually ages >50)

It is no coincidence that a deficiency is often observed in vegetarians, but also in the elderly due to reduced appetite and dental problems – which makes it difficult to eat meat.

B12 Supplements

You will usually find vitamin B12 as a food supplement in the forms of:

• Cyanocobalamin
• Methylcobalamin

But which one is better? Opinions differ on which is better, as both offer health benefits.

Cyanocobalamin is a synthetic form of vitamin B12, which, however, is considered more stable and therefore well utilized by the body.

On the other hand, methylcobalamin is the natural form of B12 and is found in food, but also in supplements. It is a more active form and has greater bioavailability (i.e. stays longer in the body), which is why it is considered better by most. Also, it is a good choice for smokers, who easily excrete cobalamin in the urine, possibly due to the intake of cyanide from tobacco.

Additionally, very often we find B12 supplements in sublingual form, rather than swallowed. In this way, the substance passes directly into the bloodstream, from the salivary glands. It thus bypasses the digestive system, during which its absorption or effectiveness may be reduced.

Furthermore, vitamin B12 works synergistically with folic acid, i.e. it has a much better effect, which is why you will often find these two together in various food supplements. It is also a key ingredient in iron formulas aimed at people with anemia, bleeding or severe fatigue. This is because of its contribution to the synthesis of red blood cells, as we have already mentioned.

For how long can I take vitamin B12?

If we are deficient in vitamin B12, we will need to take a supplement for a few months to 1 year. Usually after 3 months we should recheck its levels, in order to have a better estimate.

If the values are back to normal, in theory we can stop supplementing and check its levels once a year with tests.

However, if we do not get sufficient amounts from the diet (as in strict vegetarianism) or our bodies cannot absorb it through food, we may need to take vitamin B12 for years. In these cases, the dosage and frequency should be determined by a specialist. (15)

In the extreme case that our body is unable to absorb vitamin B12, either from food or through a supplement, it is possible that we will need B12 in injectable form, which will be decided by our doctor.(15)

Side effects

In most cases, taking it is considered safe, as it is a water-soluble vitamin, thus its excess is excreted in the urine.

Some side effects that may be seen after injectable B12 are:

• mild diarrhea
• itching or rash
• nausea and vomit
• headache
• swelling
• venous thrombosis
• pulmonary edema or congestive heart failure
• allergic reaction or anaphylaxis (rare)

Caution: Vitamin B12 in the form of cyanocobalamin (found in most dietary supplements) should be avoided by people with Leber’s disease (hereditary optic neuropathy), as it can cause severe atrophy of the optic nerve (10). However, since these patients are often deficient in vitamin B12, injectable B12 in the form of hydroxycobalamin is often chosen as part of their treatment. (11)

Is there a risk of overdose?

High doses of vitamin B12 have been associated with acne breakouts (mainly from the injectable form, not the supplement), but also negative effects in people with diabetes and kidney problems. (14)

Particular attention is needed in pregnancy, as in case of excessive intake of Vitamin B12, and subsequently high levels of it at birth (>536.8 pmol/L), the chances of an autistic disorder in the child increase. (11)

Although large doses may have side effects in some groups, generally doses up to 2,000 mcg/day are considered safe in case of deficiency. However, in this case monitoring by a specialist is needed.(14)

In conclusion

Vitamin B12 is therefore a very useful nutrient for the body, necessary for many basic functions.

In case you feel intense fatigue or face any of the problems associated with its deficiency, ask your doctor for a relevant test to check its levels in your body!