Vitamins help to regulate our metabolic processes. Vitamins were named by a Polish biochemist called Kazimierz Funk (that's a cool name!). Vitamins being the abbreviation of vita amines - 'vita' meaning life in Latin and 'amin' as he believed them to be amines (an organic compound that contains a basic nitrogen atom with a lone pair), which unfortunately we now know to be untrue (perhaps a better name would've been Funksters). Anyway, as touched upon with minerals, a lack of vitamins through our dietary sources can result in related problems. An extreme example of the effects of a prolonged lack of certain vitamins within our diet, is the disease Scurvy, which is due to a deficiency of vitamin C. Scurvy was a common disease with seafarers of old with limited food sources.
Fat-soluble vitamins - A, D, E & K - are able to be stored in the body, whereas water-soluble vitamins - B & C - are not.