Analysis of Prevalence, Magnitude, and Timing of the Dawn Phenomenon in Type 1 Diabetes—Descriptive Analysis of Two Insulin Pump Trials

To better understand the dawn phenomenon in type 1 diabetes, we sought to determine its prevalence, timing and magnitude in studies specifically designed to assess insulin pump basal requirements. Thirty-three participants from two insulin pump studies were analyzed. Twenty were obtained from a methodologically-ideal semi-automated basal analysis trial in which basal rates were determined from repeated fasting tests (the derivation set) and 13 from an artificial pancreas trial in which duration of fasting was variable (the validation set). Prevalence was determined for the total cohort and the individual trials using the standard definition of an increase in insulin exceeding 20% and lasting 90 minutes or more. Among cases, time of onset and percent change in the magnitude of basal delivery was determined. Seventeen of the 33 (52%) participants experienced the dawn phenomenon [11 of 20 (55%) in the derivation set, 6 of 13 (46%) in the validation set]. Time of onset was 3:00 am [IQR; 3:00, 4:15 am] in the derivation set and 3:00 am [3:00, 4:00 am] in the validation set. The magnitude of the dawn phenomenon was a 58.1% [28.8, 110.6%] increase in insulin requirements in the derivation set and 65.5% [45.6%, 87.4%] in the validation set. The dawn phenomenon occurs in approximately half of patients with type 1 diabetes, when present it has predictable timing of onset (generally 3am), and has substantial but highly variable magnitude. These findings imply that optimization of glycemic control requires clinical emphasis on fasted overnight basal insulin assessment.