Exercise in type 1 diabetes: real-world data on glucose levels and hypoglycaemia risk from over 420,000 exercise sessions

Aims/hypothesis This large observational cohort real-world study explored the effects of three forms of exercise (walking [WALK], aerobic excluding walking [AER] and anaerobic [ANAER]) on glucose levels and hypoglycaemia risk in type 1 diabetes. Methods Data were collected from 3248 users of mySugr Logbook and Apple Health (mean ± SD age 41.23±12.25 years; glucose management index of 7.05±1.09%; 41.5% were female) over a total of 428,058 exercise sessions. Acute and 24 h glycaemic effects were examined across exercise types. Post-exercise glycaemia data over 24 h were compared with sedentary glycaemic data. Time of exercise was used to assess the probability of nocturnal hypoglycaemia. Results Independent of type, exercise decreased glucose by −1.06±0.89 mmol/l. For the individual types of exercise, WALK decreased levels by −1.24±0.81 mmol/l, AER by −1.43±1.02 mmol/l and ANAER by −0.52±0.81 mmol/l (all p <0.001). Comparing sedentary days vs active days, the time in range (3.9–10 mmol/l glucose) increased by +2.08±6.06% for WALK, +2.94±6.46% for AER and +3.93±7.16% for ANAER, and the time below range (<3.9 mmol/l) increased by 0.37±1.57% for WALK, 0.74±1.70% for AER and 0.68±1.79% for ANAER (all p <0.001). ANAER yielded a smaller chance of acute hypoglycaemia and WALK yielded a smaller chance of nocturnal hypoglycaemia ( p <0.001). Activities done after 15:30 hours did not increase the risk of nocturnal hypoglycaemia when compared with earlier exercise sessions (+0.9±0.34%; p <0.01). Conclusions/interpretation Aerobic activities decreased glucose more during exercise sessions than anaerobic exercise and yielded larger acute hypoglycaemia risk; anaerobic activities yielded the largest 24 h glycaemic improvements. More-intense exercise resulted in a larger nocturnal hypoglycaemia than walking; exercise timing was not a relevant contributor to nocturnal hypoglycaemia.