We studied the combined effect of cool (10°C) and warm (30°C) ambient temperatures and physical exercise on insulin absorption and postprandial glycemia. Nine type I (insulin-dependent) diabetic patients were injected subcutaneously with their usual morning dose of shortand intermediate-acting human insulin and were given breakfast. Warm temperature was associated with 3- to 5-fold higher insulin absorption (P < .01) and significantly lower blood glucose concentration (P < .001) than cool temperature regardless of exercise. Exercise was associated with 28% (P < .01) and 22% (P < .05) increases in plasma insulin and maximally 5.7 mM (P < .025) and 7.1 mM (P < .01) lower blood glucose at cool and warm temperatures, respectively. Warm temperature and exercise had an additive effect in stimulating insulin absorption and in lowering blood glucose concentrations. However, there was no evidence of synergism between higher temperature and exercise in increasing free-insulin concentrations or decreasing blood glucose concentrations. To avoid postprandial hyperglycemia at cool temperature or hypoglycemia after exercise at warm temperature, appropriate adjustments in diet and insulin dose, or both, should be made.

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