In 1912 Frederick G. Hopkins and Casimir Funk suggested that specific human diseases, such as beriberi, rickets, and scurvy, were caused by the absence of certain nutritional substances in the diet. These were termed vitamins (“vital amines”), because the first such substance isolated, thiamin (vitamin B1), was an amine (a compound containing an amino group). When other such essential substances were isolated and analyzed, they proved not to be amines, but the term vitamin was retained to refer to any essential growth factor required in very small amounts. Many vitamins have been discovered since that time. Although the functions of some vitamins are unknown, many have been shown to be coenzymes. Letters of the alphabet were first used to describe the mysterious nutritional factors. These letters (A, B, C, D, E, K, and others) have persisted. It was found, however, that some factors actually consisted of more than one substance. The original B factor has been shown to consist of more than a dozen entities. These factors are now designated as specific substances, for example, thiamin (B1), riboflavin (B2), pantothenic acid (B3), and three related substances, and niacin. Because these commonly occur together, they are referred to as the B-complex vitamins. Đây là bài đọc còn ở dưới là câu hỏi. Mong mọi người giúp mình. Mình cần gấp ạ