In a small group of women with type 1 diabetes who used an artificial pancreas system, menstrual cycles weren’t linked to changes in glucose levels or insulin requirements, according to a new study published in the journal Diabetes Technology & Therapeutics.
Artifical pancreas systems — also known as closed-loop insulin delivery systems — are a combination of an insulin pump and a continuous glucose monitoring (CGM) system that communicate with each other, with the goal of seamlessly delivering insulin based on the body’s needs. These systems use a computer algorithm to predict where a person’s glucose levels are heading, anticipating any adjustments to insulin delivery that may be needed. Right now, automated insulin delivery systems are marketed to consumers as hybrid closed loop (HCL) systems, since they take over some elements of insulin delivery tasks but still require input from users. Currently, hybrid closed-loop systems are mostly geared toward automatically adjusting basal (background) insulin levels, since the combination of the CGM sensor and the insulin they use can’t detect mealtime blood glucose changes and deliver insulin to lower blood glucose quickly enough to be practical for mealtimes. That means users still have to manually program mealtime bolus doses of insulin, based on the carbohydrate content of their meal and other factors.
There are many ongoing research projects, though, that aim too develop fully closed-loop systems. These studies typically enroll small numbers of participants with type 1 diabetes to look at how many different factors affect blood glucose control and insulin delivery. The more information researchers can collect on factors that affect the body’s insulin needs and blood glucose levels, the more responsive and accurate any fully closed-loop system is likely to be. For the latest study, researchers were interested specifically in looking at how women’s menstrual cycles might affect their insulin needs.
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As noted in a Healio article on the study, a group of 16 menstruating women with type 1 and an average age of 31 took part in the research. Participants used a tracking app on their phones to record all phases of their menstrual cycle. For a hybrid closed loop system, they used a Tandem t:slim X2 insulin pump with Control-IQ technology (a proprietary algorithm) and a Dexcom G6 CGM system. Researchers then compared participants’ menstrual cycles with both CGM readings and insulin delivery over an average of 145 days per participants, spanning an average of six menstrual cycles.
Relatively stable glucose control experienced throughout menstrual cycle
Over the study’s duration, participants had an average 24-hour glucose level of 165 mg/dl during their luteal phase — the phase lasting from ovulation until the beginning of their menstrual period. During their menstrual period, participants had an average 24-hour glucose level of 161 mg/dl, and during the remainder of their cycle, they had an average daily glucose level of 159 mg/dl. The average amount of time spent in their target glucose range was 67% for the luteal phase, 69% for the menstrual phase, and 69% for the rest of the cycle. Insulin delivery also didn’t change much throughout the menstrual cycle, with a median basal rate of 0.28 U/kg during all three phases. Median daily insulin bolus rates were 0.31 U/kg during the luteal phase and 0.29 U/kg during both the menstrual phase and the rest of the cycle.
The researchers noted that the relatively stable glucose control that study participants experienced throughout their menstrual cycle doesn’t match with the real-world experiences of many women with type 1 diabetes, who sometimes experience disturbances in insulin sensitivity related to their menstrual cycle. They speculated that the automated basal insulin delivery that study participants received could be a reason for this difference — meaning that women who already have better blood glucose control may be less likely to experience large changes in insulin sensitivity related to their menstrual cycle. But further studies are needed, they wrote, to look at the impact of a hybrid closed-loop system specifically on women who report large differences in blood glucose control over the course of their menstrual cycle.
Want to learn more about diabetes and the menstrual cycle? Read “Diabetes and Your Period.”