Vitamin B12: Signs of Deficiency, Tips, and Recommended Foods

Vitamin B12, also known as cobalamin, is a water-soluble vitamin essential for the proper functioning of the nervous system and the formation of blood cells. It also plays a role in many other areas, including energy metabolism, cognitive function, nervous system balance, and reducing fatigue. This term actually encompasses four distinct compounds: hydroxocobalamin, methylcobalamin, adenosylcobalamin, and cyanocobalamin. The first three forms are naturally present in foods, while cyanocobalamin is a synthetic version. These compounds are distinguished by their bright red colour, due to the presence of cobalt.

A vitamin is considered essential because the human body cannot produce it. To meet our needs, we must therefore consume animal-based foods, such as meat, fish, eggs, and dairy products, or take dietary supplements. Our gut flora produces vitamin B12 analogs, but these cannot be absorbed by the human body (they serve only for bacterial growth).

Ingested vitamin B12 is primarily stored in the liver, which releases its reserves when needed. These reserves can be sufficient to meet the body's needs for three to five years before being depleted.

To learn more about the benefits of vitamin B12, see our article What are the benefits of vitamin B12?

Clinical symptoms

In adults, a deficiency in vitamin B12 manifests as: 

• A loss of energy

• Tingling, numbness

• Reduced sensitivity to pain

• Blurred vision

• Paleness

• Shortness of breath

• Memory loss

• Confusion

These symptoms develop gradually over several months. They are generally reversible with vitamin B12 supplementation. 

Note: If in doubt, consult a healthcare professional for a diagnosis.

Laboratory tests

Diagnosing a vitamin B12 deficiency is complex, except in specific cases. No blood test can perfectly assess vitamin B12 deficiency.  Many doctors rely on blood tests to measure vitamin B12 levels. Others argue that these tests are inadequate, especially for vegans, and that plasma methylmalonic acid (MMA) levels should be measured instead. Vitamin B12 testing is generally performed alongside folic acid testing. 

First and foremost, make sure your vitamin B12 deficiency isn’t due to a problem with absorption or storage. In these specific cases, you’ll need to address these issues first so that your body can properly absorb the vitamin B12 you’re taking later on. 

Through Diet

It is entirely possible to get enough vitamin B12 as part of a balanced vegetarian diet. In fact, vitamin B12 is found in animal-based foods such as meat, fish, eggs, seafood, or dairy products. For those following a vegan diet, finding vitamin B12 becomes far more difficult. Vitamin B12 is found naturally in certain plants (chlorella, comfrey, nori, spirulina). The problem is that these plant-based forms are not bioactive; unfortunately, our bodies are unable to utilise them. The only reliable vegan sources of vitamin B12 are fortified foods (including certain plant-based milks, some soy products, and breakfast cereals) and vitamin B12 supplements.

Excerpt from the ANSES Ciqual table.

Through supplementation

To follow a plant-based diet without developing deficiencies, vegans should follow one of these recommendations: 

• Eat fortified foods two to three times a day to get at least 3 µg of vitamin B12.

• Take a supplement that provides 10 µg of vitamin B12 daily. 

• Take a weekly supplement that provides 2,000 µg of vitamin B12.

As a general guideline, an adult should consume at least 4 µg of vitamin B12 per day. A pregnant woman should consume 4.5 µg/day, and a breastfeeding woman 5 µg/day.

The Different Forms of Vitamin B12

Cobalamin exists in various forms: cyanocobalamin, methylcobalamin, hydroxocobalamin, and adenosylcobalamin. In the intestines, all these supplemental forms have relatively similar absorption rates. They are therefore equivalent in terms of intestinal bioavailability (the actual amount of vitamin B12 that reaches its site of action and the speed at which it does so). It should be noted that methylcobalamin is the predominant form found in eggs and milk. Only the cyanocobalamin form is absent from our diet (synthetic form).

1. For non-vegans: Include animal-based foods in your daily diet, such as eggs, fish, meat, and dairy products

2. For people who have trouble absorbing vitamin B12: Take care of your gut microbiota. Inflammation can cause intestinal malabsorption. A diet rich in fibre and fermented foods will help enrich your microbiota. A diet low in sugar and processed foods will limit inflammation

3. For people who have trouble storing vitamin B12: Consider supporting your liver’s detoxification process. Certain plants, such as milk thistle or black radish, can help with this

4. For vegans: Choose foods fortified with vitamin B12 or consider taking supplements

Vitamin B12 is a water-soluble vitamin; excess amounts are easily eliminated through stool or urine or stored in the liver. 

To date, no toxicity has been demonstrated.

Excessive intake could trigger an immune reaction, causing skin inflammation. Nausea, dizziness, or hot flashes may also occur.

When taking supplements, always follow the doses recommended by the manufacturer. Self-medication is not advised. Always consult your doctor.

Vitamin B12 works in synergy with vitamin B9: they play a role in energy metabolism and energy production in the mitochondria. Both ensure the proper functioning of the methylation cycle, specifically the synthesis of methionine from homocysteine. This is why it's beneficial to combine your intake of vitamin B12 with that of vitamin B9. Foods rich in folate (vitamin B9) include: brewer's yeast, green vegetables, nuts, lentils, aged cheeses, etc.

Emilie is a biochemistry and natural active ingredients engineer. Emilie is also a naturopath, nutrition adviser and writer specialising in health, nutrition and wellbeing. She has worked for over 10 years in the pharmaceutical industry and in scientific communication, which gives her a comprehensive understanding of health and enables her to discuss the subject with authority and clarity. Science is her foundation; words are her tools. She advocates a more preventative, more reasoned, more scientific and, of course, more natural approach to health!