Vitamin B12 Deficiency: Symptoms and Treatment

Vitamin B12 is an essential vitamin our bodies need, but it’s unique because it’s a vitamin only found in animal products (as a bacterial product). Vitamin B12 deficiency is a common health problem among vegetarians and vegans. While other essential vitamins and minerals can be consumed through plant sources, vitamin B12 cannot.

The relative difficulty in getting vitamin B12 through dietary sources may have made the body’s use of B12 more efficient. It is the only water-soluble vitamin – which includes all B vitamins and vitamin C – that is stored in the body.

However, vitamin B12 deficiencies do happen, especially if you’re a vegan who’s not taking a vitamin B12 supplement. You may not notice any symptoms of the deficiency at all, or you could be seriously ill without knowing this deficiency is the cause. It is this last point that highlights the importance of correcting a deficiency, even if you only see it on a blood test. So what are the symptoms of vitamin B12 deficiency, and how do we best treat it?

Symptoms of Vitamin B12 Deficiency

Vitamin B12 deficiency is traditionally known to cause megaloblastic anaemia, where the red blood cells are too large and under-functioning. However, a high folate intake can hide it, as this vitamin also helps to regulate red blood cell size. The scarier, harder to reverse symptoms of vitamin B12 deficiency are neurological and psychiatric.

Numbness and paresthesia, which is a perceived burning or prickling feeling, are the most common neurological symptoms of B12 deficiency. Ataxia, sensory impairments, poor memory, and even delusions and hallucinations are some of the other problems that come with severe deficiency.  In many cases, neurological problems come before any changes to the red blood cells, so normal blood cell counts don’t mean your levels are adequate.

How Bad Can Associated Health Problems Get?


A severe, prolonged vitamin B12 deficiency can have terrible consequences. In one unusual case study, a 52-year-old woman went without a correct diagnosis for two years after developing anxiety, low mood, unusual muscle movements and hallucinations. After antidepressants, antipsychotics and even electroconvulsive treatments, only some symptoms had improved and her quality of life was still very poor. However, several months of vitamin B12 supplementation gradually improved her health, until she no longer had any symptoms. No other cause of her illness could be found, so it appears that serious vitamin B12 deficiency was the only answer. This is a very unusual case, as a lack of vitamin B12 is rarely the only cause of mental illness.

What Causes a Vitamin B12 Deficiency?

Vitamin B12 deficiency is caused by either a low intake, such as vegetarian and vegan diets without supplementation or poor absorption. For example, taking medications such as proton pump inhibitors (PPIs), which reduce stomach acid production, can impair digestion. A case-control study showed that being on PPIs for at least two years was linked to a 65% higher risk of B12 deficiency. If the participants took at least 1.5 pills a day, their risk was 95% higher. Stomach acid breaks down protein in foods and aids the absorption of certain nutrients. So, if you need to reduce its production, supplementation with vitamin B12 is best to compensate.

Metformin is another medication linked to vitamin B12 deficiency. Each one-gram dose increase of the drug is associated with almost triple the risk of low B12 levels. Metformin is a common medication used to control blood sugar in type II diabetes. However, its effects are being explored in other areas such as forming part of potential antiaging protocols. A B12 supplement could help you to maximize the efficacy of your treatment while reducing negative effects.

Besides medication, another cause of B12 deficiency is damage to the gut wall from inflammation. Unaddressed food intolerances are one way this inflammation can be triggered, including those to gluten. In fact, some research suggests that gluten may cause some degree of inflammation in everyone. If your vitamin B12 levels are low, food intolerance testing could be worth your time.

Vitamin B12 Deficiency Treatment


Treating vitamin B12 deficiency involves removing the cause if possible, and increasing your intake through diet or supplementation. As for dietary sources, you can expect to absorb around two-thirds of the vitamin B12 in chicken, 56-89% in lamb or mutton, and 42% of vitamin B12 in fish. Eggs are not a good B12 source, as less than 10% is actually bioavailable to humans. There may even be at least one plant source of vitamin B12, in the form of green and purple nori. Nori is the flat sheets of seaweed you see in sushi.

When it comes to supplementation, we have injectable and oral options. Oral supplementation can be just as effective as injections, so don’t worry if you’re afraid of needles. In studies where people with deficiencies took 2,000ug of vitamin B12 every day for four months, or 1,000ug in gradually-tapered doses, their levels increased just as much. Their neurological health and blood cell count improved to the same degree as people receiving injections, too. However, they didn’t have underlying conditions such as Crohn’s disease or coeliac disease, where absorption is affected. You may need injections in the case of illnesses that cause malabsorption.


If I need supplements, what form should I take? The most common type of vitamin B12 you can purchase is cyanocobalamin, but it’s not the most bioavailable. Methylcobalamin, hydroxocobalamin and adenosylcobalamin are easier to absorb for people with genetic differences that affect methylation. For your body to use cyanocobalamin, the cyanide part must be split off so the cobalamin can be activated.  This activation step isn’t as efficient if you have a methylation impairment, which can be picked up by a genetic test. It is important to get your genes tested if you have mental health or other neurological issues because of these variations, in order to get the right treatment. For example, methylation impairments often also require supplementation with pre-activated folate (5-MTHF). You may only find partial relief if you just take vitamin B12.

Vitamin B12 is fundamentally important for your neurological health, but conditions and certain medications that affect nutrient absorption can get in the way.

If you suspect that you have a B12 deficiency, it’s best to test both your levels of the vitamin and your genes for possible methylation difficulties. Your genes can be the difference between simply needing to change your diet, and needing to take high-quality supplements. Try our CircleDNA testing kit to find out which vitamins you have higher needs! This can also help figure out what your optimal diet might be.

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