Every March, Americans lose an hour to daylight‑saving time, a shift linked to heart attacks and fatal crashes. Researchers at Stanford Medicine modeled three clock policies—permanent standard time, permanent daylight‑saving time, and the current biannual switch to see how each reshapes circadian rhythms and downstream health. Their analysis shows the status quo strains the body’s internal clock the most.

The model translates sunrise and sunset data into a “circadian burden” metric, measuring how much a person’s 24‑hour clock must adjust. Results indicate permanent standard time minimizes burden for the majority, especially those in western zone edges, while about 15 % of early‑birds would benefit from permanent daylight‑saving time’s extra evening light. Morning light exposure proves especially critical.

Linking burden to disease prevalence, the authors estimate permanent standard time would cut obesity by 0.78 percentage points, preventing roughly 2.6 million cases, and reduce stroke by 0.09 points, about 300,000 fewer events. Permanent daylight‑saving time yields smaller gains. The study, funded by the NIH, stops short of accounting for real‑world light exposure variations, but provides the strongest health‑centric evidence yet for ending the clock shuffle. Policymakers can now cite concrete health data.