Heightened Thiamine and Gholine Requirements in Tropical Heat

Keys 1 recently dismissed our findings of heightened thiamine and choline requirements in tropical heat with the brief statement that they were unconvincing. The only basis given for his conclusion was his own study of human subjects exposed to high temperatures for only one week or less. In this brief interval of heat exposure, he failed to find any improvement in work performance with accessory vitamin administration (with men on regular army rations).

Reference to the published literature would have shown that no deficiency effects should have been expected in so short a period. Rat growth and food consumption rates begin to show the influence of vitamin deficiency only during the second (or some subsequent) week. This was plainly stated and made clear in the data presented in our paper on heightened thiamine need in the heat. 2 Others 3 have shown that the metabolic adaptation to change in environmental temperature begins in the second week of exposure and is largely accomplished by the end of the third week. Human tests covering one week or less therefore have no valid bearing upon the problem and provide no basis for a conviction one way or another.

Since any real heightening of vitamin requirement in tropical heat is a matter of great importance in human and animal nutrition, it is well to eliminate every possible uncertainty. With all vitamins added to our diet mixture and new food given only once or twice a week, it was possible that the destruction of thiamine and choline was more rapid in the feed jars at 90°F than at 68 °F and that this may have been the basis of the apparent heightening in requirement.