Vitamin B2 (riboflavin)

Riboflavin (vitamin B2) is a water-soluble B vitamin that the body converts into two coenzymes — FAD and FMN — which are essential for the chemical reactions that release energy from carbohydrate, fat and protein. It is also needed to activate vitamin B6 and to help recycle folate and process other nutrients, so a shortage tends to ripple into the wider B-vitamin system. It is found widely in dairy, eggs, lean meat, green vegetables and fortified cereals, and because the body stores little of it, intake needs to be regular; however, frank deficiency is uncommon on a mixed diet in well-fed populations. When deficiency does occur — for example with poor diet, alcohol dependence, certain absorption problems, or in combination with other B-vitamin shortages — it produces a recognisable picture: cracked, sore corners of the mouth (angular cheilitis), cracked lips, a smooth, sore, magenta-coloured tongue, a greasy scaly rash around the nose, and sometimes anaemia. In practice riboflavin is seldom measured as a plain blood level (which fluctuates with recent intake); status is better judged clinically or with a specialist red-cell enzyme test (the erythrocyte glutathione reductase activation coefficient, EGRAC).

• Recent intake or supplements — a high level mostly reflects diet or a B-complex supplement and is not harmful; excess is passed in the urine (often turning it bright yellow).
• Not a clinically useful 'high' — riboflavin has no toxicity of concern, so a raised level is not acted upon.

• Dietary deficiency — poor or restricted diet, especially low in dairy and animal foods.
• Alcohol dependence — reduced intake and absorption.
• Malabsorption — conditions affecting the gut.
• Combined B-vitamin deficiency — B2 shortage often travels with B6, folate and others.
• Increased needs — pregnancy and breastfeeding.