Long-term data from the world’s largest four-day workweek trial has revealed sustained mental health improvements that challenge traditional productivity assumptions. The UK study, tracking 61 companies and 3,300 employees since 2022, shows remarkable consistency in psychological benefits:
- 78% of participants maintain significantly lower stress levels
- Anxiety and depression scores remain 42% below baseline
- Sleep duration increased by an average of 1.2 hours weekly
- 86% report better work-life integration
Neurological findings are particularly compelling. MRI scans of participants show reduced cortisol-related hippocampal shrinkage—a biomarker of chronic stress reversal. Equally important, productivity metrics stayed stable or improved in 92% of companies, with revenue growth averaging 1.4% quarterly despite reduced hours.
The mechanisms behind these benefits are multifaceted. Employees report having time for preventive health behaviors (exercise, meal prep) that buffer against stress. The extra weekday often goes toward caregiving responsibilities, reducing the “mental load” that particularly burdens working parents. Perhaps counterintuitively, the time constraint appears to enhance focus—meeting durations dropped 35% as companies eliminated low-value activities.
However, the study identified crucial implementation factors. Successful transitions required:
- Output-based (not hours-based) performance metrics
- Cross-training to ensure coverage without burnout
- “Meeting hygiene” protocols
- Leadership embracing the model fully
Sectors with continuous operations (healthcare, manufacturing) faced unique challenges, developing rotating schedules with careful fatigue monitoring. As the data matures, it suggests four-day weeks may be more sustainable for mental health than temporary perks like meditation apps. Over 550 UK companies have now adopted the model permanently, while U.S. pilot programs are expanding rapidly in 2024.
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