B12 is involved in producing red blood cells, maintaining a healthy nervous system, and converting food to energy. It also helps to regulate the immune system and mood, it controls the levels of the amino acid, homocysteine, (elevated levels of which are associated with heart disease). Most people who eat meat, fish, eggs and dairy products, consume enough B12. Vegans are advised to eat fortified food and take supplements.

How much do I need? The UK government says adults need 1.5 micrograms (mcg) a day, the US National Institutes of Health advises 2.4 mcg, and the European Food Safety Authority says 4 mcg a day is adequate. The US and Europe, but not the UK, recommend higher levels for pregnant and breastfeeding women. A study published last year found one in 12 women aged between 19 and 39 were B12 deficient, despite consuming at least the UK recommended minimum intake.

What are the symptoms and causes of B12 deficiency? Symptoms include fatigue, faintness, headaches, pale skin, loss of appetite, weight loss, ‘pins and needles’ and a sore, red tongue. One of the main causes is the autoimmune condition, known as pernicious anaemia. Other causes are conditions affecting the stomach or small intestine, such as Crohn’s disease and operations such as gastrectomies ,(which involve removal of part of the stomach), and certain medications.