The Ecology of Human Sleep (EcoSleep) Project: Protocol for a longitudinal cohort repeated-measurement-burst study to assess the relationship between sleep determinants and sleep outcomes under real-world conditions across time of year
Authors: Biller Anna M , Fatima Nayab , Hamberger Chrysanth , Hainke Laura , Plankl Verena , Nadeem Amna , Kramer Achim , Hecht Martin , Spitschan Manuel 
Published: February 2024

Introduction

The interplay of daily life factors, including mood, physical activity, or light exposure, influences sleep architecture and quality. Laboratory-based studies often isolate these determinants to establish causality, thereby sacrificing ecological validity. Furthermore, little is known about time-of-year changes in sleep and circadian-related variables at high resolution, including the magnitude of individual change across time of year under real-world conditions.

Objectives

This study investigates the combined impact of sleep determinants on individuals’ daily sleep episodes to elucidate which waking events modify sleep patterns. A second goal is to describe high-resolution individual sleep and circadian-related changes across the year to understand intra- and interindividual variability.

Methods and analysis

This study is a prospective cohort study with a measurement-burst design. Healthy adults aged 18-35 (N= 12) will be enrolled for 12 months. Participants will continuously wear actimeters and pendant-attached light loggers. A subgroup will also measure interstitial fluid glucose levels (n= 6). Every four weeks, all participants will undergo three consecutive measurement days of four ecological momentary assessments each day (“bursts”) to sample sleep determinants during wake. Participants will also continuously wear temperature loggers (iButtons) during the bursts. Body weight will be captured before and after the bursts, and visual function will be tested in the laboratory. The bursts are separated by two at-home electroencephalogram (EEG) recordings each night. Circadian phase and amplitude will be determined during the bursts from hair follicles, and habitual melatonin onset will be derived through saliva sampling. Environmental parameters (bedroom temperature, humidity, and air pressure) will be recorded continuously.

Ethics and dissemination

The Ethics Committee of the Technical University of Munich approved this study (#2023-653-S-SB). We adhere to research standards including the Declaration of Helsinki and open science principles. Results will be made available as future peer-reviewed publications and contributions to conferences.

Article summary – Strengths and Limitations

This study investigates human sleep in the natural environment across 12 months incorporating multi-domain sleep determinants to understand their combined contribution to the subsequent sleep episode.

The study integrates novel and state-of-the art data collection methods, including wearable at-home EEG, continuous glucose measurement (CGM) and personalised light logging, as well as hair follicle-derived circadian amplitude and phase.

The study focuses on longitudinal and high-resolution intra-individual data (N= 12) going beyond sparse resolution. Assessments include home-based EEG recordings twice per month, monthly circadian phase and amplitude assessment, 3-days of four daily ecological momentary assessment per month, and continuous actimetry, continuous light logging and continuous bedroom temperature/humidity/air pressure monitoring.

Due to the lack of experimental manipulations, drawing direct causal inferences from the data will not be possible.

The participant burden to generate the within-subject data is high due to the intensive sampling and long participation duration.