Will Switching from Daylight to Standard Time Harm Your Health?

Daylight savings time will come to an end on November 2, 2025.  In the fall, Americans turn back the clock overnight, resulting in one less hour of sleep. Scientists don’t agree, though, on the health implications of switching from daylight to standard time.

Switching from Daylight to Standard Time Could Upset Natural Rhythms:

A Stanford University study published in the Proceedings of the National Academy of Sciences suggests that going back and forth between standard time and daylight savings time disrupts circadian rhythms (PNAS-USA, Sep. 23, 2025). The researchers found evidence that altering normal rhythms could increase the risk for obesity and stroke. They calculated that sticking with standard time year-round would prevent 300,000 strokes each year and cut down on obesity. People who usually stay up late suffer greater biological consequences from shifts in time regimens. In most states, this happens twice a year, once in the spring as we go into daylight savings time and once in the fall as we retreat from it.

Time Shifts May Not Change Rates of Heart Attacks:

Previous research on moving from daylight to standard time and vice versa blamed these changes for higher rates of car crashes and heart attacks. That may have inspired the Stanford scientists.

However, researchers at Duke University have just published their analysis of data from 168,870 patients over the course of a decade (JAMA Network Open, Sep. 9, 2025). The study in JAMA Network Open found no differences in heart attack rates in the weeks before and after changing from daylight to standard time or the reverse. In addition, they found no increase in stroke or mortality.

How Should Policymakers Respond?

These dueling findings could leave policy makers in a quandary. Should we stop switching times twice a year, because of the possible risks involved, or is it actually relatively safe to switch into and out of daylight savings time? Clearly, the answer is the common and extremely unsatisfying conclusion: more research is needed.

We welcome your comments on time and what you see as the pros or cons of twice-yearly shifts in time-keeping. Please feel free to share this post using the icons at the top of the page.