The effect of ambient temperature on glucose tolerance.

Standard (75 g) oral glucose tolerance tests were performed at two different ambient temperatures (23 and 33 degrees C) in random order in 16 (eight obese) diabetic and 16 (eight obese) non-diabetic Nigerian subjects. Consistently higher plasma glucose values were found 120 min post-glucose ingestion at 33 degrees C, with mean differences of 0.5 (SE 0.3) and 4.5 (SE 1.5) mmol l-1 in the non-diabetic and diabetic subjects, respectively. This caused reclassification of two of the non-diabetic subjects as Impaired Glucose Tolerance at 33 degrees C, applying the WHO criteria. The difference was consistently greater (p less than 0.01) in the non-obese subjects (non-diabetic 0.8 (0.4), diabetic 6.9 (2.8) mmol l-1) than in the obese (non-diabetic 0.2 (0.4), diabetic 2.1 (0.9) mmol l-1). In the diabetic subjects, a negative correlation (r = -0.50, p less than 0.01) was established between the difference and the body mass index. This variability in responses to ambient temperature between the obese and non-obese subjects could be due to a variable influence of heat on arm blood flow consequent on differences in amounts of subcutaneous fat. The ambient temperature for the conduct of the oral glucose tolerance test is important.