Metabolic and Cognitive Consequences of Noise-induced Sleep Disturbance

This study will investigate the biological mechanisms linking sleep disruption by noise and the development of disease. In a laboratory sleep study, we will play traffic sounds of different types (road, rail and air) and noise levels during the night. We will also have nights with sound from so-called "white noise machines". These generate a low-level and continuous noise that may improve sleep by "masking" the traffic noises that would otherwise disturb sleep. We will also measure objective sleep quality and quantity, cognitive performance across multiple domains, self-reported sleep and wellbeing outcomes, and blood samples. Blood samples will be analysed to identify metabolic changes in different nights. Identifying biomarkers that are impacted by sleep fragmentation will establish the currently unclear pathways by which chronic noise exposure at night can lead to the development of diseases in the long term, especially cardiometabolic disorders.

The experimental sleep study has the overarching goal of deepening our understanding of experimentally-induced disruption of sleep and changes in metabolic and cognitive function, and to determine the efficacy of a potential non-pharmacological intervention to promote sleep. To this end, the study will address the following independent aims:

Aim 1: Determine associations between novel physiologic markers of sleep and metabolic and cognitive function. We will measure the sleep of healthy volunteers using novel and classical indictors of sleep architecture. Each morning we will obtain blood samples for metabolomics analysis and administer a neurocognitive test battery.

Aim 2: Determine the biological and neurobehavioral consequences of noise-disrupted sleep. We will compare effects on sleep, metabolomics and cognitive function between quiet nights and nights with traffic noise.

Aim 3: Evaluate the effects of continuous pink noise throughout the night. Sub-aim 1: To determine if continuous noise (pink noise) per se improves or disturbs sleep, we will investigate changes in novel and classical indictors of sleep architecture and disturbance induced by pink noise relative to quiet baseline nights. Sub-aim 2: To determine if pink noise reduces sleep disturbance by traffic noise, we will investigate changes in sleep fragmentation and continuity, and cortical and autonomic arousal, from nights with both traffic noise and pink noise compared to nights with traffic noise only.

The study will be conducted at in the University of Gothenburg sound environment laboratory (SEL). The SEL is a high fidelity research laboratory equipped to simulate a typical apartment, including three individually light-, sound- and vibration-isolated private bedrooms. Ceiling mounted speakers in each room allow us to create a realistic acoustic environment by transmitting sound exposures from the control room to each bedroom individually.

This study has a prospective within-subjects cross-over design. Participants (N=12) will each spend five consecutive nights in the SEL with a sleep opportunity between 23:00-07:00. Daytime sleep will be prohibited, confirmed with measures of daytime activity via wrist actigraphy monitors worn continuously throughout the study. Three subjects will take part concurrently, in separate bedrooms. The first night is a habituation period to the study protocol and for familiarisation with the test procedures. Study nights 2-5 are the experimental nights and will be randomly assigned across participants using a Latin square design to avoid first-order carryover effects. Each subject will be exposed to one night of each of the following:

Quiet night: No noise will be played, serving as a control night to assess individual baseline sleep, metabolic profile, and cognitive performance; Traffic noise night to determine consequences of noise-disrupted sleep; Pink noise night: To determine impact of continuous pink noise on sleep; Traffic + pink noise night: simultaneous traffic and pink noise at the same sound pressure levels as in the traffic-only and pink noise-only nights, to determine sleep-protecting effects of pink noise in the face of traffic noise.

Each night we will record physiologic sleep with polysomnography (PSG) and cardiac activity with electrocardiography (ECG). Each study morning, subjects will provide a 2ml blood sample, complete cognitive testing and answer questionnaires and will depart the SEL to follow their normal daytime routine. They will return to the SEL at 20:00 each evening to prepare for sleep measurements. Caffeine will be prohibited after 15:00 and alcohol will be prohibited at all times. Because sound-induced auditory fatigue may be affected by noise exposure during participant's normal routines,60 they will wear a noise dosimeter during the week of the study to record their daytime noise exposure. Because extreme and/or variable dietary behaviour can affect the metabolome/lipoprotein profile, participants will be given guidance that they should eat a similar evening meal on each day of the laboratory study, confirmed with a food diary, The actual meal itself can be different for different study participants, because the study has a within-subjects design.

Sleep will be recorded with ambulatory polysomnography (PSG) and cardiac activity with electrocardiography (ECG) and finger pulse photoplethysmogram. Data are recorded offline onto the sleep recorder, and will be downloaded and checked every study morning to ensure data quality. In addition to traditional sleep analysis performed by the research group at the University of Gothenburg, raw PSG data will be used to calculate the Odds Ratio Project, a novel metric of sleep depth and stability.

Each study morning subjects will provide a 2 ml blood sample for plasma metabolomics analysis. To ensure reliable data, blood samples will be taken at the same time every day to mitigate circadian effects, before eating or drinking anything except water, and each sample will be handled in the same way i.e. centrifuged, aliquoted and stored in -80C freezers. Subjects will eat the same food each study evening to mitigate within-subject dietary effects on the blood metabolome.

Each morning, subjects will complete a computerised cognitive test battery taking approximately 20 minutes, that includes 10 tests across a range of cognitive domains (motor praxis, visual object learning, fractal 2-back, abstract matching, line orientation, emotion recognition, matrix reasoning, digit symbol substitution, balloon analog risk, psychomotor vigilance). Cognition data will be analysed to determine key measures of cognitive speed and accuracy, adjusting for practice effects and the difficulty of the stimulus set.

Subjects will complete a battery of one-time validated questionnaires to measure their general health (SF-36), chronotype, noise sensitivity, habitual sleep quality, environmental sensitivity, and annoyance and sleep disturbance by noise. Subjects will also answer a questionnaire each study evening and morning, involving questions on sleepiness (Karolinska Sleepiness Scale), auditory fatigue, sleep disturbance by noise, and validated sleep and disturbance questions.

Subjects will wear a noise dosimeter during the week of the study to record their daytime noise exposure (sound pressure level only, no actual sound recordings).

Participants will wear a wrist actigraphy monitor continuously throughout the study period, and also for the week before the study, to confirm habitual sleep-wake times and to measure physical activity levels.

Eligibility Criteria:
Inclusion Criteria:

1) live in or around the city of Gothenburg area (Sweden)

Exclusion Criteria:

1. aged \<18 or \>30 years;
2. habitual sleep and wake timings more than ±1 hour different from the study sleep times (i.e. habitual sleep time should be 22:00-00:00 and habitual wake time should be 06:00-08:00);
3. BMI\>25 kg/m2;
4. regular sleep medication use (prescribed or "over-the-counter");
5. poor hearing acuity (measured during screening via pure tone audiometry);
6. diagnosed with sleep disorders;
7. indications of sleep apnea on the STOP-BANG questionnaire;
8. shift work;
9. smoking, vaping, snus, or other nicotine use;
10. pre-existing use of "white noise machines" as a sleep aid.