Vitamin B12, also known as cobalamin, is a unique nutrient, as it’s the only vitamin we require that must be sourced externally from animal-derived foods or supplements.

So how do we know if we are getting enough of it? What are the symptoms we should be looking out for if we are lacking it? And what problems can a deficiency in this vitamin lead to?

To answer these questions, it’s first worth thinking about the role vitamin B12 plays in maintaining our overall health.

Vitamin B12 is essential not only for its role in helping to create new cells in the body, but also in the stabilisation of the nervous system. It plays a crucial role in the production of red blood cells, vital in ensuring effective transportation of oxygen around our body, and it is also heavily involved in the development of the protective covering around nerve cells, called myelin.

Sometimes patients will present with classical symptoms suggestive of a deficiency, and it may be these that raise the suspicion of a lack of Vitamin B12. The most common of these is probably fatigue or lack of energy, and given the vital role vitamin B12 plays in red cell synthesis it’s not uncommon for a particular type of anaemia, called megaloblastic anaemia, to develop. An untreated deficiency can also result in neurological symptoms, such as pins and needles in the extremities, or difficulty walking. Some patients have even reported cognitive effects such as difficulty concentrating or persistent low mood. Finally, a lack of B12 can cause distinctive changes to the tongue, called glossitis, where the tongue becomes sore and swollen and may have a typical ‘beef steak’ appearance. Mouth ulcers may also develop.

As we get our B12 through our diet, deficiency is often due to the fact that we are not eating enough of it. A vegan diet has traditionally been considered high risk due to animal-derived foods being a primary source of vitamin B12. But deficiency may also be due to the body’s inability to absorb B12. Pernicious Anaemia is an autoimmune disease that can cause this that sometimes runs in families. In this condition your body inadvertently makes antibodies against a protein called Intrinsic Factor, vital in ensuring effective absorption of vitamin B12 in your gut. Other conditions that affect the bowel can also affect absorption of B12 such as Crohn’s disease or coeliac disease. Certain drugs, can affect the absorption of B12 too, most notably the anti-diabetic drug metformin and various anti-epileptic medications.

So surely there’s a blood test to confirm the diagnosis? Well, yes and no - it isn’t always entirely straightforward. A traditional Vitamin B12 blood test may only assess the total B12 - a measurement of all forms of B12 present in the body - but we know that not all varieties of B12 are immediately available for use. For that reason, it may also be worth assessing the levels of Active B12 in the blood to provide a more accurate picture of B12 status. This is not a widely available option, but the Vitamin B12 blood test available at One Day Tests offers this as standard.

There’s also a degree of controversy regarding the accuracy of Vitamin B12 blood tests. It’s generally agreed that a Vitamin B12 level of lower than 200 nanograms/L is sensitive enough to diagnose 97% of people with a deficiency, but levels in the blood don’t easily correlate with clinical symptoms. Equally, blood serum values can be maintained even as stores are becoming depleted, so even if your results appear to be in the normal range, it’s not impossible that you may still have a vitamin B12 deficiency.

If there is uncertainty regarding the diagnosis, it may be worth considering performing a further blood test for Homocysteine which, along with Methylmalonic acid (MMA), is often raised in cases of vitamin B12 deficiency. Currently there is no definitive test - both homocysteine and MMA can be raised for a variety of other reasons - but interpreted alongside your vitamin B12 level and any symptoms you might be experiencing, they will increase the chances of knowing for certain whether you may have a deficiency and require vitamin B12 supplementation.