The Effect of Environmental Temperature on Glucose and Insulin After an Oral Glucose Tolerance Test in Healthy Young Men.
OBJECTIVE
The purpose of this study was to compare glucose and insulin responses during an oral glucose tolerance test (OGTT) in cold (C), neutral (N), and hot (H) environments.


METHODS
Eleven males completed three 4-hour climate-controlled OGTT trials (C, 7.2°C; N, 22°C; and H, 43°C). Participants remained semireclined for 60 minutes before ingesting a 1.8 g/kg glucose beverage. Skin and rectal core temperatures were continuously monitored. Blood was collected just before glucose ingestion (time 0) and at 15, 30, 60, 90, 120, and 180 minutes, and analyzed for serum glucose, insulin, hematocrit, and hemoglobin. Expired gases were collected upon entering the chamber (-60 minutes), before glucose ingestion (0 minutes), and at 60, 120, and 180 minutes to determine V(O2) and respiratory exchange ratio.


RESULTS
Rectal core temperature was greater in the H condition compared with both C and N (P < .001). Rectal core temperature was not different between C and N, whereas skin temperature was different across all trials (H greater than N greater than C). The V(O2) was greater in C than in both H and N during all time points. Carbohydrate oxidation was greater in C compared with H and N (P < 0.001). Glucose was higher during H compared with C and N (P ≤ 0.002). Glucose was elevated in C compared with N. Insulin was higher in H compared with C (P = 0.009). Area under the curve for serum glucose was greater in H compared with C and N (P ≤ 0.001); however, there was no significant difference in area under the curve for insulin.


CONCLUSIONS
These data indicate that after an OGTT, glucose and insulin are elevated in a hot environment.
Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT (Drs Dumke and Ruby, and Messrs. Cuddy, Hailes, and Rose). Electronic address: charles.dumke@umontana.edu.
Charles L
CL
Dumke
School of Health, Physical Education and Recreation, University of Nebraska at Omaha, Omaha, NE (Dr Slivka).
Dustin R
DR
Slivka
Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT (Drs Dumke and Ruby, and Messrs. Cuddy, Hailes, and Rose).
John S
JS
Cuddy
Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT (Drs Dumke and Ruby, and Messrs. Cuddy, Hailes, and Rose).
Walter S
WS
Hailes
Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT (Drs Dumke and Ruby, and Messrs. Cuddy, Hailes, and Rose).
Shawn M
SM
Rose
Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT (Drs Dumke and Ruby, and Messrs. Cuddy, Hailes, and Rose).
Brent C
BC
Ruby
D001786:Blood Glucose / Q000032:analysis*; D001831:Body Temperature; D003080:Cold Temperature; D004734:Energy Metabolism; D005951:Glucose Tolerance Test; D006358:Hot Temperature; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008297:Male; D009009:Montana; D012881:Skin Temperature; D055815:Young Adult
D001786:Blood Glucose; D007328:Insulin
cold; environmental stress; heat; oral glucose tolerance test