The B complex vitamins comprise a class of eight water-soluble vitamins which all have important roles to play in cell metabolism. Although these B vitamins are all chemically different, they are often found together in food sources and so are grouped together and share similar names. Dietary supplements with all eight B vitamins are usually referred to as the vitamin B complex.
This complex did originally number sequentially from 1-12, but it was later discovered that the substances numbered B4, B8, B10 and B11 did not meet the qualifications to be classed as a vitamin, meaning that they were either endogenously synthesised or not essential for human life.
B vitamins are present in most whole foods, but processing usually reduces their value, so many countries are legally required to reinforce refined flour and cereal products with supplemental vitamins B1, 2, 3 and 9 to prevent deficiencies.
Particularly concentrated sources of B complex vitamins are found in turkey, liver and tuna fish, while good sources also include whole grains, legumes, chilli peppers, potatoes, molasses, bananas and nutritional yeast products. B12 most often requires supplementation, especially for vegans, as it is not usually available from plant sources.