OBJECTIVETo quantify variability of insulin requirements during closed-loop insulin delivery. RESEARCH DESIGN AND METHODSWe retrospectively analyzed overnight, daytime, and total daily insulin amounts delivered during a multicenter closed-loop trial involving 32 adults with type 1 diabetes. Participants applied hybrid day-and-night closed-loop insulin delivery under free-living home conditions over 12 weeks. The coefficient of variation was adopted to measure variability of insulin requirements in individual subjects. RESULTSData were analyzed from 1,918 nights, 1,883 daytime periods and 1,564 total days characterized by closed-loop use over 85% of time. Variability of overnight insulin requirements (mean [SD] coefficient of variation 31% [4]) was nearly twice as high as variability of total daily requirements (17% [3], P < 0.001) and was also higher than variability of daytime insulin requirements (22% [4], P < 0.001). CONCLUSIONSOvernight insulin requirements were significantly more variable than daytime and total daily amounts. This may explain why some people with type 1 diabetes report frustrating variability in morning glycemia.Closed-loop insulin delivery is an emerging treatment modality for people with type 1 diabetes (1). Multiweek free-living overnight or day-and-night home investigations demonstrated improved glycemic control and reduced hypoglycemia with hybrid closed-loop compared with conventional sensor-augmented pump therapy (2-4). Insulin delivery modulated by closed-loop systems reflects the amount of insulin required in real time, which may vary from night to night and from day to day. The present investigation measures night-to-night and day-to-day variability of insulin requirements in adults with type 1 diabetes over 12 weeks of closed-loop insulin delivery (2). RESEARCH DESIGN AND METHODSWe retrospectively analyzed overnight (2300-0700 h), daytime (0700-2300 h), and total daily (midnight to midnight) insulin delivery during a closed-loop period in a multicenter (U.K., Germany, and Austria), randomized crossover study involving 32 subjects with type 1 diabetes and conducted in free-living home settings (2).

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