The effect of ambient temperature on glucose tolerance and its implications for the tropics

There have been a few reports in Caucasians that glucose tolerance is worse at higher environmental temperatures. In investigating these observations in a tropical African population, we performed standard oral glucose tolerance tests in the morning after overnight fasting in 16 diabetic (with varying glycaemic control) and 16 nondiabetic subjects, both groups with differing body weights. Each volunteer ingested 75 g glucose at two different ambient temperatures of 22-23 degrees C and 32-33 degrees C in random order. These room temperatures are typically observed during hot and humid seasons in sub-Saharan Africa. Our results confirm that glucose tolerance was worse at the higher room temperature (p less than 0.01). The post-oral glucose 2 h values at the lower room temperature were lower by about 5 mmol/l in the diabetics and 0.5 mmol/l in the non-diabetics (both p less than 0.02). Similarly, the total and incremental areas under the 2 h glucose/time curves were greater at the higher room temperature. These results were not influenced by obesity. We conclude that glucose tolerance in tropical Africans is dependent on environmental temperature. An ambient temperature for the performance of diagnostic oral glucose tolerance test should therefore be specified, especially when evaluating differences in diabetes prevalence rates in populations resident in different climatic regions.