A study of changes in insulin requirements related to the menstrual cycle in Japanese women with type 1 diabetes using the advanced hybrid closed‐loop system

ABSTRACT Aims/Introduction In type 1 diabetes (T1D), insulin requirements and glycemic control may vary across the menstrual cycle. We examined phase‐related differences in insulin requirements, glycemic metrics, and recorded carbohydrate amounts in women using an advanced hybrid closed‐loop (AHCL) system and their associations with menstrual symptoms and premenstrual dysphoric disorder (PMDD) screening status. Materials and Methods Fifteen premenopausal women with T1D using the MiniMed 780G without hormonal therapy were analyzed. Cycles with ≥2 eligible days (SmartGuard ≥70%) in both early follicular (d1–7) and late‐luteal (d‐7 to −1) phases were included. Phase differences were assessed using linear mixed‐effects models. Associations between phase‐related changes and menstrual symptom scores and PMDD screening status were evaluated using Spearman correlation and the Mann–Whitney U test, respectively. Results Eighty cycles were analyzed. Compared with the early follicular phase, the late‐luteal phase showed a higher total daily insulin dose (49.2 ± 3.7 vs 45.1 ± 3.7 U/day), basal insulin dose, total bolus insulin, and recorded carbohydrate amount (197.9 ± 18.2 vs 186.1 ± 18.2 g/day), with lower Time in Range (70.0 ± 3.2% vs 72.9 ± 3.2%) and higher Time above Range (TAR). Most phase‐related differences persisted after adjustment for recorded carbohydrate amount. No clear associations between menstrual symptom scores or PMDD screening status and phase‐related changes were detected. Conclusion During AHCL therapy, insulin requirements increased and glycemic control modestly worsened in the late‐luteal phase. No clear associations between phase‐related metabolic changes and menstrual symptom scores or PMDD screening status were detected in this small cohort.