VITAMINS 339 



higher animals and most phints involves coupling ol the DPN + -flavin- 

 cytochrome-protein systems. 



Requirements 



It is even more difficult to arrive at daily allowances for niacin than 

 lor thiamine and riboflavin. Most species synthesize nicotinamide, 

 but the quantity depends upon the diet. Animals can use nicotinic 

 acid as well as the amide. Neither is essential under favorable dietary 

 conditions if the supply of tryptophan is adequate. Thus proteins 

 rich in this amino acid are helpful but can prove inadequate compared 

 to free tryptophan. Apparently dietary tryptophan is not converted 

 to niacin extensively enough in all cases. 



Recommended daily allowances range from 5 mg. for infants to 

 10 to 20 mg. for adults, depending on age, sex, and activity. These 

 intakes are believed to provide a safety factor for the uncertainties in 

 the effect of diets and the possible activity of intestinal bacteria. 

 Starting chicks should receive about 8 mg. of nicotinic acid per lb. of 

 feed, but no recommendations have been made for laying and breeding 

 hens. Daily nicotinic acid allowances for growing pigs range from 

 7 to 21 nig., depending on age and weight. Ruminating animals do 

 not require dietary niacin. 



Meats, fish, and yeast are perhaps the best sources of the factor. 

 Green vegetables, milk, and eggs are effective, the last two because 

 of the tryptojjhan present, since they are almost devoid of nicotin- 

 amide. Corn is not a good source unless steeped in alkali first. This 

 treatment yields substances con\'crted to niacin. Other cereal grains 

 are not satisfactory when the outer layers are removed. White floiu" 

 is low in nicotinamide, so it is customary to enrich it for bread, using 

 synthetic material at about $10/kg. Since the vitamin is stable to 

 heating, oxidation, and the pH values encoiuitered in all foods, 

 processing does no harm except in cases of physical removal. 



Deficiency 



Lack of nicotinamide and its substitutes, nicotinic acid and tryp- 

 tophan, leads to pellagra, often in complicated form with other defi- 

 ciencies present. Digestive disturbances accompany the appearance 

 of inflamed areas of the skin, predominantly of the face and hands. 

 Later the skin becomes scaly, rough, and pigmented brown; finally 

 open sores develop. The tongue swells and ulcerates, weight is lost 

 rapidly, and neural symptoms appear leading to insanity and death. 

 Before brain lesions develop and nerve injury becomes acute, treat- 

 ment with niacin is rapidly and rather completely effective. The 



