Vitamin B2 (Riboflavin)

Riboflavin, also known as vitamin B2, is an easily absorbed micronutrient with a key role in maintaining health. Vitamin B2 is required for a wide variety of cellular processes. Like the other B vitamins, it plays a key role in energy metabolism, and is required for the metabolism of fats, ketone bodies, carbohydrates, and proteins.
Milk, cheese, leafy green vegetables, liver, kidneys, legumes such as mature soybeans, yeast, almonds and rock lobsters are good sources of vitamin B2, but exposure to light destroys vitamin B2. Marmite is also a good source of vitamin B2.
Vitamin B2 is not toxic when taken orally, as its low solubility keeps it from being absorbed in dangerous amounts from the gut. Although toxic doses can be administered by injection, any excess at nutritionally relevant doses is excreted in the urine, imparting a bright yellow colour when in large quantities.
Vitamin B2 is usually produced commercially by fermentation processes involving bacteria and fungi, specially bred for the job.
Vitamin B2 is yellow or yellow-orange in colour and in addition to being used as a food colouring (E101) it is also used to fortify some foods. It is difficult to incorporate vitamin B2 into many liquid products because it has poor solubility in water. Hence the requirement for riboflavin-5'-phosphate (E101a), a more expensive but more soluble form of riboflavin.
Vitamin B2 is continuously excreted in the urine of healthy individuals, making deficiency relatively common when dietary intake is insufficient. However, vitamin B2 deficiency is always accompanied by deficiency of other vitamins.
A deficiency of vitamin B2 can be primary - poor vitamin sources in one's daily diet - or secondary, which may be a result of conditions that affect absorption in the intestine, the body not being able to use the vitamin, or an increase in the excretion of the vitamin from the body.
In humans, signs and symptoms of vitamin B2 deficiency (ariboflavinosis) include cracked and red lips, inflammation of the lining of mouth and tongue, mouth ulcers, cracks at the corners of the mouth (angular cheilitis), and a sore throat. A deficiency may also cause dry and scaling skin, fluid in the mucous membranes, and iron-deficiency anaemia. The eyes may also become bloodshot, itchy, watery and sensitive to bright light.
The overt clinical signs of vitamin B2 deficiency are rarely seen among inhabitants of the developed countries. However, there is a common 'sub-clinical' stage. Although the effects of long-term sub-clinical vitamin B2 deficiency are unknown, in children this deficiency results in reduced growth. Subclinical vitamin B2 deficiency has also been observed in women taking oral contraceptives, in the elderly, in people with eating disorders, and in various diseases. The fact that vitamin B2 deficiency does not immediately lead to gross clinical manifestations indicates that there is tight regulation of body levels.