The genesis and growth of tumors. V. Effects of varying the level of B vitamins in the diet.

As parts of a broad, integrated program on nu trition in relation to cancer, the influence of under feeding, caloric restriction, and the proportions of fat and protein in the diet of mice have been in vestigated (9-12). The work reported in this pub lication deals with the possible modification of tu mor formation consequent to varying certain B vitamins from dietary levels considered to repre sent minimal requirements for mice to amounts several-fold higher. Two experiments are con cerned with the spontaneous mammary carcinoma and two with skin tumors deliberately induced with chemical carcinogens. Vitamins of the B complex were chosen for these investigations on the assumption that large dietary differences in these essentials may exert a more significant influence on metabolism—and, therefore, possibly on carcinogenesis—than might other vitamins. Particularly, the consequences of stepwise gradation of six vitamins were studied: thiamine, riboflavin, pyridoxine, pantothenate, niacin, and choline. The minimal dietary require ments for the first four are known with a fair de gree of accuracy. The needs for niacin and choline and the remaining known members of the B com plex have not been defined for mice; apparently, they were adequately supplied by the small amounts in the "vitamin-free" casein and yeast ex