Assessing health, wellbeing, and working life impacts of a 4-day week: a multimodal protocol

Long working hours can negatively affect workers' health, wellbeing, and work performance. Previous trials reducing working time have found improvements in multiple aspects of wellbeing, including sleep, job satisfaction, and reduced burnout, while maintaining performance. However, the potential psychological and biological mechanisms underlying these improvements, including immune function and brain function, remain unexplored. Therefore, the aim of this study is to understand the bidirectional relationship between working patterns and physical and mental health, and how workplace performance is affected. We aim to test at least 150 working-age adults in the UK (approximately half with a working time reduction and no loss of salary, and half controls with no change in working patterns) in a 14-week trial, including a 2-week baseline period, with additional participants completing questionnaires only. The primary outcome measure is the difference in physical and mental health from baseline to the end of the trial among participants undergoing a reduction in working time, compared with the control group. Data collection is currently underway, and while the majority of employers in the working time reduction group adopt a 4-day week format, the specific change in working patterns is flexible and varies between employers according to their operational need, including a 9-day fortnight, two half-days and shorter working days. Core variables include brain structure and function, sleep, immune function, interoception (perception of bodily sensations), time use, diet, mental health, and workplace performance and engagement. Secondary outcomes include weekly monitoring of self-reported wellbeing changes to identify key inflection points and assess whether these are maintained at a 6-month follow-up. Overall, this study aims to generate highly novel multimodal data on the psychological and biological implications of working time reduction, including observed changes in health, wellbeing, and performance.