Vitamin B12 is an essential water-soluble vitamin that's found in virtually all meat products and certain algae, such as seaweed. It helps maintain healthy nerve and red blood cells and is also needed to make DNA, the genetic material in all cells.

As vitamin B12 is bound to the protein in food, the acid in your stomach releases it during digestion. Once released, it combines with a substance called intrinsic factor before being absorbed into the bloodstream. Pernicious anaemia (an autoimmune condition) prevents absorption by stopping the production of intrinsic factor and is the leading cause of vitamin B12 deficiency.

Our test measures levels of the biologically-active component of vitamin B12 - thought to be the best early indicator of vitamin B12 deficiency. Around 70% of the vitamin B12 in your blood is inactive, which means it isn't available for your body to use. The human body can store several years' worth of vitamin B12. However, if you have pernicious anaemia, are vegetarian or vegan, or have recently had gastric bypass surgery - you are at a greater risk of deficiency.

Even if you get enough vitamin B12 in your diet, if your body doesn't absorb it properly, you can become deficient in vitamin B12. People who may have absorption problems include the elderly, people with low stomach acid (including those taking PPIs), people who drink excessive alcohol, and people with inflammatory bowel conditions like Crohn's or Coeliac disease.

Symptoms of vitamin B12 deficiency include fatigue and weakness, headaches, feeling faint, pale skin, palpitations and pins and needles. Vitamin B12 deficiency symptoms usually develop gradually but can worsen if the condition goes untreated. Vitamin B12 is necessary to form healthy red blood cells. A deficiency can cause red blood cells to become enlarged (macrocytic), which affects their ability to transport oxygen around the body.

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