Overview

• Modeling published in PNAS estimates that permanent standard time could lower obesity prevalence by 0.78% and stroke by 0.09%, roughly 2.6 million fewer people with obesity and 300,000 fewer strokes.
• Permanent daylight saving time also showed benefits in the model but smaller ones, with about 1.7 million fewer people with obesity and 220,000 fewer strokes compared with biannual clock changes.
• The analysis used a circadian model assuming fixed sleep and work schedules and matched estimated circadian burden to CDC county-level health data, a design the authors note has important real‑world limitations.
• Projected effects varied by chronotype and location within time zones, with greater circadian burden for people living farther west and differing impacts for morning larks versus night owls under current switching.
• Short-term harms tied to the spring shift are well documented in prior studies, including increases in heart attacks, traffic crashes, and workplace injuries, while policy remains unsettled as the 2022 Senate-passed Sunshine Protection Act awaits House action and medical groups back ending clock changes or adopting permanent standard time.