Reduction of insulin resistance in 14–15-year-old students after the COVID-19 pandemic: a prospective study from Tsunan, Japan

Introduction: A significant increase in HOMA-IR values has been reported in children after the COVID-19 pandemic. This study aimed to investigate how the changes of HOMA-IR after COVID-19 was post-pandemic (2023-2024). Materials and methods: The study included 462 students aged 14-15 from Tsunan Town, Japan, who underwent health examinations between 2015 and 2024 (258 boys, 204 girls). The students' HOMA-IR, BMI, and obesity levels were studied, and temporal changes were assessed using the Kruskal-Wallis test. IR was defined as HOMA-IR ≥2.5 and temporal changes were assessed using the chi-square test. Results: A significant change in the median HOMA-IR was observed over the 10-year period (p < 0.001). The proportion of IR was significantly higher in 2020, 2021, and 2022 (p < 0.001). Conversely, no significant differences were observed in the median BMI and obesity levels over the 10-year period (p = 0.18, p = 0.13). Significant correlations were observed between HOMA-IR and BMI as well as obesity levels throughout the entire observation period and from 2015 to 2019. However, no significant correlations were observed in the years 2020-2024. Discussion: The significant increase in HOMA-IR observed after 2020 significantly decreased to values similar to pre-COVID-19 levels by 2023. However, BMI and obesity levels showed no temporal changes. Our findings suggest that changes in lifestyle due to the COVID-19 pandemic during 2020-2022 may have influenced IR in 14-15-year-old students, irrespective of obesity status.