A comparison of the rates of clock-based nocturnal hypoglycemia and hypoglycemia whilst asleep among people living with diabetes: findings from the Hypo-METRICS study

Introduction Nocturnal hypoglycemia is generally calculated between 00:00 and 06:00. However, those hours may not accurately reflect sleeping patterns and it is unknown whether this leads to bias. We therefore compared hypoglycemia rates whilst asleep to those of clock-based nocturnal hypoglycemia in adults with type 1 (T1D) or insulin-treated type 2 diabetes (T2D). Methods Participants from the Hypo-METRICS study wore a blinded continuous glucose monitor and a Fitbit Charge 4 activity monitor for 10 weeks. They recorded details of episodes of hypoglycemia using a smartphone app. Sensor-detected hypoglycemia (SDH) and person-reported hypoglycemia (PRH) were categorized as nocturnal (00:00-06:00hrs) vs diurnal and whilst asleep vs awake defined by Fitbit sleeping intervals. Paired sample Wilcoxon tests were used to examine the differences in hypoglycemia rates. Results 574 participants (47% T1D, 45% women, 89% White, median (IQR) age 56 (45-66) years and HbA1c 7.3% (6.8-8.0)) were included. Median sleep duration was 6.1h (5.2-6.8), bedtime and waking time approximately 23:30 and 07:30 respectively. There were higher median weekly rates of SDH and PRH whilst asleep than clock-based nocturnal SDH and PRH among people with T1D, especially for SDH<70 mg/dL (1.7 vs 1.4, p<0.001). Higher weekly rates of SDH whilst asleep than nocturnal SDH were found among people with T2D, especially for SDH<70 mg/dL (0.8 vs 0.7, p<0.001). Conclusion Using 00:00 to 06:00 as a proxy for sleeping hours may underestimate hypoglycemia whilst asleep. Future hypoglycemia research should consider the use of sleep trackers to record sleep and reflect hypoglycemia whilst asleep more accurately.