396 THE BIOCHEMISTRY OF B VITAMINS 



The symptoms associated with B vitamin deficiencies are consequently 

 of a broad and general nature, 3 affecting all the organs and systems of 

 the animal. Neurological symptoms are manifest psychiatrically and by 

 both central and peripheral neurological malfunction and degeneration. 4 

 Cardiovascular and gastrointestinal symptoms are almost invariably 

 found. Epithelial degeneration is characteristic, and hematological and 

 endocrinological involvements are pronounced in deficiencies of at least 

 some of the B vitamins. A more detailed consideration of specific defi- 

 ciencies follows in a later section, but it is important to emphasize at 

 this point the general nature of the symptomatology, which frequently 

 makes clinical diagnoses of avitaminoses extremely difficult. A conse- 

 quence of this fact is that much of our knowledge concerning deficiencies 

 has come from "epidemiological" studies, where the disease was deduced 

 from the nature of the diet. Largely as a result of this development, a 

 diagnosis of an avitaminosis in an individual living in a generally well 

 nourished population area is seldom made, and our understanding of 

 individual differences in requirements and of subclinical vitamin defi- 

 ciencies is a recent but only slowly progressing effort to remedy this. 2, 5 - 6 



B Vitamin deficiencies generally occur as the result of an unbalanced 

 diet, and when a dietary intake is so poor as to bring the level of one 

 B vitamin below a critical level, it rather frequently happens that 

 more than one vitamin is lacking in the diet in adequate amounts. Con- 

 sequently, many of the classical pictures of deficiency are actually com- 

 pound deficiencies, and clear-cut clinical cases involving a deficiency of 

 one and only one nutritional factor are seldom seen. 7-12 This fact is 

 exemplified by the many difficulties experienced by most earlier workers, 

 and in some cases by workers even today, in producing diets for animal 

 experimentation which are lacking in only the factor under study. 13 As a 

 result of the compound nature of most clinical avitaminoses, there is a 

 great wealth of practical information available on the pathology of 

 naturally occurring deficiency diseases, but much less information on the 

 picture involved in any particular B vitamin deficiency. In considering 

 clinical data bearing upon the medical aspects of deficiency, it is there- 

 fore most important to keep in mind the probable complex nature of the 

 deficiency. Moreover, many case reports from nonendemic populations 

 involve deficiencies secondary to some other affliction, in which case the 

 symptomatology is similarly a complex one in which the distribution of 

 symptoms between a number of causative factors is difficult if not im- 

 possible to analyze. 14, 15 



Finally, there is a growing realization at present that the incipient 

 early stages of deficiency may manifest themselves over extended periods 

 in individuals upon a slightly submarginal B vitamin intake. 16 The 



