How are nighttime blood oxygen levels related to changes in sleep spindles, and are these relationships predictive of the development of dementia? While both hypoxia and sleep spindle characteristics have been independently linked to cognitive decline, the associational structures remain unclear.
We used mediation analysis. The exposure was nocturnal oxygenation (SpO2 and hypoxic burden). The mediators were spindle characteristics (density, chirp, and spindle-SO coupling phase). The outcome was based on longitudinal follow-up of dementia. The mediation analysis told us the percentage of the total exposure-outcome association that can be explained by the mediators, while adjusting for demographic and clinical covariates.
We used the Sleep Heart Health Study visit 1 (SHHS-1) from NSRR, which included the Framingham Heart Study Offspring cohort (FHS-OS) and the Atherosclerosis Risk in Communities (ARIC) study. The mean age was 61.5 years, with 50.1% female, all White, and a median body mass index of 28.7kg/m2. The dementia mean follow-up was 16.7 years.
Spindle density consistently mediated the relationship between nocturnal oxygenation and dementia risk. Higher average NREM SpO2 (from 90% to 98%) was associated with increased spindle density and a 137.0-day delay to dementia diagnosis (p= .024; 26.6% mediated). A lower hypoxic burden (from the 80th percentile [85.2% min/hour] to the 20th percentile [22.4% min/hour]) was associated with increased spindle density and a 43.4-day delay in dementia diagnosis (p= .046; 69.1% mediated). Spindle chirp and spindle-SO coupling phase were not significant mediators after adjustment.
The findings suggest a physiological associational pathway linking oxygenation, sleep spindles, and dementia, with spindle density as a mediator. It generates a hypothesis that interventions that improve nighttime oxygenation (e.g., CPAP) may help preserve brain health by enhancing spindle activity, offering a possible avenue to delay dementia onset.
https://github.com/vkatragadda1/mediation_spo2_spindles_shhs
https://doi.org/10.1093/sleep/zsaf401
Impaired spindle activity and hypoxia have both been linked to dementia. However, their association structures remain unclear. We conducted a mediation analysis in 2023 adults from Sleep Heart Health Study Visit 1 with adjudicated dementia outcomes from the Framingham Offspring and Atherosclerosis Risk in Communities cohorts (median follow-up: 21.0 years; 394 events). Exposures included desaturation-removed SpO2 during non-rapid eye movement (NREM) sleep and hypoxic burden (cumulative desaturations ≥2% min/hour); mediators included spindle density, spindle chirp, and spindle-SO coupling phase. Time-to-dementia was modeled using Weibull survival regression with covariate adjustment and demographic stratification; evaluation metrics included C-index and time-dependent area under the curve. Mean age was 61.5 years; 50.1% were female. One non-White participant was excluded due to potential SpO2 measurement bias. Spindle density significantly mediated both exposures with strong model performance (C-index 0.78 [95% CI = 0.73 to 0.82]; AUC10 0.83 [95% CI = 0.71 to 0.95]). For NREM SpO2, a 90% versus 98% SpO2 was associated with increased spindle density and a 137.0-day delay to dementia diagnosis (95% CI = 10.6 to 352.1 days; p = .024; 26.6% mediated). For hypoxic burden, a 20th percentile (22.35% min/hour) versus 80th percentile (85.24% min/hour) burden was correlated with increased spindle density and a 43.4-day delay to dementia diagnosis (95% CI = 1.1 to 92.9 days; p = .046; 69.1% mediated). The SpO2 exposure-mediator correlation was unexpectedly negative, potentially from limited age variability and statistical suppression. Mediation effects remained consistent across covariates and subgroups. The oxygenation-spindle pathway may represent a physiologic mechanism for time-to-dementia and modifiable marker for established oxygenation interventions.
Katragadda, V., Azarbarzin, A., Thomas, R. J., Mullington, J. M., & Sun, H. (n.d.). Linking nocturnal blood oxygen, sleep spindles, and dementia: A retrospective cohort mediation analysis in middle-aged and older adults. Sleep. https://doi.org/10.1093/sleep/zsaf401
Guest Blogger: Dr. Haoqi Sun, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA