People with type 1 diabetes have significantly more variable overnight insulin requirements than during the day, a new study reports.
Researchers at the University of Cambridge wanted to quantify how insulin requirements varied during closed-loop insulin delivery.
A closed-loop system is where an insulin pump works in conjunction with a continuous glucose monitor (CGM). The two devices are connected to a program which works out how much insulin is needed in response to blood glucose readings from the CGM.
32 adults with type 1 diabetes were given insulin during a multicentre closed-loop trial, and researchers evaluated their overnight, daytime and total daily insulin amounts. The participants were monitored under free-living home conditions.
They were monitored over 1,918 nights, 1,883 daytime periods and 1,564 total days characterised by closed-loop use during 85 per cent of the study period.
Variability of overnight insulin requirements (50 to 300 per cent) were nearly twice as high as variability of total daily requirements (70 to 200 per cent), and higher than daytime insulin (50 to 200 per cent).
The researchers concluded: “The main strength of the current study is the quantification of variability of insulin requirements derived from data collected over a prolonged period under free-living conditions reflecting participants’ insulin needs in real-life.
“The present analysis pinpoints the reasons why people with type 1 diabetes benefit from closed-loop insulin delivery and indicates that greatest benefit may apply overnight when insulin requirements are most variable and realtime adaptive insulin delivery is most desirable.”
The study team noted that several factors could have contributed to insulin requirements varying more overnight. These included evening meal composition, the effects of daytime exercise, variable insulin absorptio, changes in insulin sensitivity induced by stress, and menstrual cycle phases in women.
“This may explain why some people with type 1 diabetes report frustrating variability in morning glycemia,” the authors added.
The findings appear in Diabetes Care.

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