Q.How are vitamins classified

Vitamins are small organic compounds the body cannot synthesise and must obtain through diet; needed only in small amounts, they mostly act as coenzymes rather than as fuel, and both deficiency and excess can cause disease. The name derives from 'vital amines', after the earliest vitamins identified.

They split into two solubility classes. Fat-soluble vitamins (A, D, E, K) are absorbed with fatty food and stored in fatty tissue/liver. Water-soluble vitamins (the B-complex -- B1 thiamine, B2 riboflavin, B3 niacin, B5 pantothenic acid, B6 pyridoxine, B7 biotin, B9 folic acid, B12 cobalamin -- plus vitamin C) cannot be stored and are excreted if in excess, so must be supplied regularly; the missing B-numbers (B4, B8, B10, B11) mark subs …