This study investigates the relationship between sleep patterns, glycemic control, and brain health in adults, with a particular focus on middle-aged individuals, including those with normal weight as well as those with overweight or obesity-the latter representing a demographic at elevated risk for type 2 diabetes (T2D). Individual sleep exposures such as sleep duration, sleep quality, sleep timing, and sleep regularity have all been associated with impaired glucose metabolism and indicators of compromised brain health. However, well-controlled studies that comprehensively examine how overall sleep health-considering all these dimensions-is related to both glycemic control and brain health remain limited.
To address this research aim, participants will be recruited from two Swedish sites: Dalarna and Uppsala. Following enrollment and an on-site baseline assessment session, participants' lifestyle behaviors will be monitored over 14 consecutive days. Specifically, nighttime sleep will be assessed using a wearable, FDA-cleared sleep device (SleepImage); 24-hour interstitial glucose levels will be tracked via a continuous glucose monitor (CGM); and physical activity will be recorded using a wrist-worn activity tracker (Fitbit). During this monitoring period, participants will also log their dietary intake and mood through smartphone-based assessments. After the 14-day monitoring period, participants will return for a concluding on-site session.
During the on-site sessions or the 14-day monitoring period, biological samples will be collected to assess metabolic, hormonal, inflammatory, and neurodegenerative biomarkers. Blood samples will be analyzed for markers such as sex hormones, HbA1c, C-reactive protein (CRP), leptin, ghrelin, adiponectin, and brain health indicators including brain-derived tau and neurofilament light chain (NfL), in addition to broader proteomic and metabolomic profiles. Stool samples will also be collected for further analyses. In addition to providing biological samples, all participants-provided they meet inclusion criteria and give informed consent-will undergo structural brain imaging using magnetic resonance imaging (MRI). Cognitive assessments will include verbal fluency tasks and validated psychological instruments to evaluate mood and cognitive function.
The entire protocol will be repeated after one year, allowing for the assessment of longitudinal changes in sleep patterns, metabolic health, and brain function over time.
The primary aim of the NNF study is to investigate both cross-sectional and longitudinal associations between sleep patterns-measured over two consecutive weeks at baseline and again one year later-and indicators of glycemic control and brain health in a cohort of middle-aged adults. Secondary aims include, for example, exploring how sleep patterns relate to variability in protein and metabolite abundances in blood, among other metabolic, cognitive, and biological outcomes detailed below.
