A [¹¹C]PBR28 PET study on the associations between sleep health and microglial density

Sleep disturbances and inflammation are interconnected through shared regulatory mechanisms and are both implicated in age-related diseases. However, their connection at the level of brain-specific inflammation remains underexamined in humans. This study investigated whether specific dimensions of sleep are associated with microglial density, as measured by translocator protein (TSPO) levels, a biomarker of neuroinflammation. TSPO levels were measured using a single [¹¹C]PBR28 positron emission tomography (PET) scan in 39 healthy adults aged 50-81 years (M_age = 66.7, SD = 8.9; 19 females, 20 males). Sleep dimensions were assessed using the Karolinska Sleep Questionnaire on three occasions over five years, twice before and once around the time of PET imaging. Shorter sleep, more frequent napping, daytime fatigue, and sleep insufficiency were associated with higher TSPO levels in the middle frontal cortex (MFC). Conversely, longer sleep was associated with higher TSPO levels in the hippocampus and putamen. Exploratory factor analysis and bootstrapping confirmed a negative association between a factor representing shorter sleep and MFC TSPO levels. Additionally, a greater deviation from optimal sleep duration over the five years, in either direction from eight hours, was associated with higher current TSPO levels in all but one examined brain regions. Peripheral C-reactive protein levels did not significantly correlate with the sleep variables or TSPO levels in any of the brain regions. Analyses were adjusted for age and sex. These findings suggest that insufficient and prolonged sleep durations are associated with elevated microglial density in frontostriatal and limbic systems, respectively, among healthy middle-aged and older adults, without any associations with peripheral inflammation. Further longitudinal studies are needed to clarify directionality and whether changes in sleep duration over time may serve as early indicators of brain health.