The complex comprises a number of factors differing widely in chemical structure, most of which have been found to be essential in human nutrition. Many of these vitamins are components of one or more coenzymes which function importantly in intermediate metabolism. Such roles have been demonstrated for thiamine, riboflavin, niacin, pyridoxine and pantothenic acid. It seems likely that the “anti-anemic” vitamins, folic acid and vita-min B12, will be found to act in a similar manner. Choline, often considered a member of the B complex, is undoubtedly important in human nutrition but is not an essential dietary constituent as it may be formed in the body from other compounds. Presumably man requires biotin, but little is known about the function of this vita-min. Inositol has not been shown to be essential in human nutrition.
Deficiency of vitamins of the B complex is one of the forms of malnutrition encountered frequently in medical practice. Since many of the B vitamins have a common distribution in foods, multiple deficiency is observed more often than deficiency of a single compound. Since some of these vitamins are closely interrelated in metabolic processes, the clinical signs of deficiency may be similar when the dietary supply of any one of several factors is inadequate. Hypervitaminosis is not a problem with members of the B group of vitamins because amounts in excess of requirement are excreted in the urine.
Numerous pathologic states may be precipitating or contributary causes of vitamin B complex deficiency. Diseases in which the metabolic rate is. above normal, such as hyperthyroidism, febrile states or leukemia, increase the requirement of thiamine and probably also of riboflavin and niacin although definitive data are not available for the last two vitamins. Since these vitamins function in the metabolism of carbohydrate, requirement is in-creased when diets are high in starch and sugar or when intravenous glucose is used as the sole source of alimentation. It seems likely that need may be increased following severe trauma.
The B vitamins may be poorly absorbed or lost from the body in diarrheal diseases, inflammatory lesions of the intestinal tract and in congestive heart failure or other conditions associated with edema of the intestinal mucosa. There is evidence that vitamin B complex deficiency per se may cause poor absorption from the intestinal tract. Malabsorption is demonstrated by flat glucose and fat tolerance tests and abnormalities in the roentgenographic appearance of the small intestine. The changes observed following barium administration consist of loss of the normal “herringbone” pattern, hypersegmentation and disturbances in motility.
In diabetes mellitus and cirrhosis of the liver, signs of vitamin B complex deficiency are observed frequently. In both conditions, vitamin utilization may be defective and in the latter disease, anorexia and an inadequate in-take of these factors are the usual findings.
At times, administration of certain antibiotics may lead to vitamin deficiency although under other circumstances antibiotics may spare vitamin requirement (83). The possibility that prolonged antibiotic therapy may induce deficiency must be kept in mind. Lesions suggestive of deficiency must be differentiated from similar change due to complicating fungus infections which are not uncommon.