Insulin levels early in perimenopause inform vasomotor symptom incidence across the menopausal transition.

Context: Metabolic health and body mass index (BMI) has been implicated in influencing menopause-related changes, but the role of elevated insulin, an early marker of metabolic dysfunction, remains understudied. Objective: To determine whether midlife fasting insulin is associated with menopausal changes such as vasomotor symptom incidence and reproductive hormone trajectories. Methods: This study consisted of longitudinal analyses of 704 community-based participants from the Study of Women's Health Across the Nation (SWAN). It included data from baseline to the 10th annual visit, restricted to women who had age-47 fasting insulin measurements. Main outcome measures included timing and duration of hot flashes, night sweats, cold sweats, and vaginal dryness, and trajectories of estradiol, follicle-stimulating hormone, and testosterone from 6 years before to 6 years after the final menstrual period. Results: Higher fasting insulin levels during early perimenopause predicted earlier onset of hot flashes and night sweats, longer duration of hot flashes and cold sweats, and greater increases in testosterone. In Cox proportional hazards models, elevated age-47 insulin was associated with a higher hazard of hot flashes and cold sweats; the association between insulin and hot flash likelihood remained significant when BMI was incorporated as a covariate. BMI associations with vasomotor symptoms paralleled those of insulin levels, but BMI appeared to be more closely associated with slower estradiol decline and blunted FSH rise. Conclusions: Perimenopausal fasting insulin and BMI show complementary but distinct associations with menopausal changes. Elevated insulin predicts earlier and prolonged vasomotor symptoms, and is also associated with higher testosterone levels.