Low skeletal muscle mass independently predicts the progression of insulin resistance in non-obese older adults: a six-year cohort study.

Objectives: To investigate whether low skeletal muscle mass predicts insulin resistance (IR) progression in non-obese older adults, and whether its coexistence with abdominal obesity further increases risk. Methods: This six-year cohort study was part of the Tanno-Sobetsu study, a prospective cohort of 204 community-dwelling Japanese older adults aged ≥ 65 years, enrolled in 2017 and followed through 2023. Participants were classified into four groups based on the presence or absence of low skeletal muscle mass (sex-specific lowest quartile) and abdominal obesity. IR progression was defined as HOMA-IR ≥ 1.73. Participants without IR at baseline were followed for a median of 2.8 years. Cox proportional hazards models were used to estimate adjusted hazard ratios (HR) for IR progression, using the group with neither condition as the reference, with adjustments for age, sex, baseline HOMA-IR, and triglycerides. Results: During follow-up, 86 participants (42.2%) developed IR. Compared to those with neither condition, low skeletal muscle mass alone was significantly associated with IR progression (HR: 2.11, 95% CI 1.08-4.11, Conclusions: Low skeletal muscle mass independently predicted IR progression in older adults, even in the absence of abdominal obesity. No additive risk was observed when low muscle mass coexisted with abdominal obesity after adjusting for baseline HOMA-IR. These findings support assessing muscle mass for IR prevention, regardless of abdominal obesity status. Supplementary Information: The online version contains supplementary material available at 10.1007/s13340-025-00843-9.