Age‐related population level decoupling of obstructive sleep apnea severity from body mass index: Insights from over 40,000 patients across the adult lifespan

Study Objectives Obesity is a major determinant of obstructive sleep apnea (OSA) severity, but its influence may vary across adulthood. We examined age‐related patterns of body mass index (BMI), apnea–hypopnea index (AHI), and hypoxemic burden, and assessed whether the association between BMI and OSA severity attenuates with age. Methods We analyzed 32,031 men and 10,572 women aged 20–90 years who underwent overnight polysomnography for suspected OSA. Segmented linear regression with a prespecified knot at 50 years evaluated age‐associated differences in BMI, AHI, and hypoxemia adjusted for clinic site and testing year. Pearson correlations between BMI and AHI and between BMI and hypoxemia were calculated across 10‐year age bins with differences tested using Fisher's r‐to‐z transformation. Results BMI increased up to midlife and declined at older ages in both sexes, whereas AHI and hypoxemia increased with age. In men, age‐related increases in AHI and hypoxemia were attenuated after midlife, whereas in women AHI slope did not change significantly. BMI–AHI and BMI–hypoxemia correlations were moderate in midlife but weakened at older ages, particularly in men. Fisher's comparisons confirmed significant attenuation in older men, with less consistent findings in women. Conclusions These findings demonstrate an age‐related decoupling between adiposity and OSA severity. BMI becomes a less informative marker of OSA severity in older individuals, particularly in men, suggesting increasing contributions of BMI‐independent mechanisms with aging.