Glucose Variability Around Exercise Persists in Insulin-Independent Human Islet Transplant Recipients

Glucose regulation around exercise is a major challenge for individuals with type 1 diabetes. Although clinical islet transplantation (ITx) prevents severe hypoglycemia, animal studies suggest that glucose regulation around exercise after ITx may not be normal. We hypothesized that changes in blood glucose (as estimated by continuous glucose monitoring [CGM]) during moderate aerobic exercise and glucose variability (estimated by CGM standard deviation) post-exercise would be greater in ITx patients than those observed in control participants. On 2 separate days, 6 insulin-independent ITx individuals and 6 matched controls performed either 45 minutes of moderate cycling (60% of VO2 max) or 45 minutes of seated rest. Sessions were performed at the same time of day (late afternoon), in random order, separated by at least 48 hours. Participants were asked to replicate food timing and composition as closely as possible. ITx were matched with controls for age (50.0 vs. 50.0 years), height (165.2 cm vs. 165.8 cm), weight (63.3 kg vs. 65.5 kg), sex and physical activity levels. Exercise caused a significant decrease in CGM glucose in ITx participants (from 6.0±0.7 to 5.4±0.8 mmol/L; p=0.007) but not in matched controls (from 5.2±0.7 to 4.9±0.3; ns). During the 6 hours following exercise, mean CGM glucose levels were higher (7.9±1.1 vs. 5.7±0.6; p=0.002) and glucose variability was greater (CGM glucose SD 1.7±0.7 vs. 1.2±0.3; p=0.02) in ITx participants compared to controls. These data suggest that despite insulin independence, exercise-induced glucose variability persists in islet transplant recipients.