Without Biannual Time Shift, Prevalence of Obesity, Stroke May Be Reduced

WEDNESDAY, Sept. 17, 2025 (HealthDay News) — The prevalence of obesity and stroke would be reduced with permanent Standard Time (SDT) and Daylight Saving Time (DST) compared with the current Biannual Shifting (BAS) in the United States, according to a study published online Sept. 15 in the Proceedings of the National Academy of Sciences.

Lara Weed and Jamie M. Zeitzer, Ph.D., from Stanford University in California, estimated the impact of permanent SDT or DST on health by modeling the circadian impact of SDT, DST, and BAS across a year in the United States.

The researchers found that compared with either permanent SDT or DST, BAS produces a greater burden on the circadian system, with chronotype and location (latitude and location within time zones) affecting the burden. There would be a decrease in the prevalence of obesity and stroke under SDT compared with the current policy under idealized light exposure conditions and after controlling for health and socioeconomic factors (−0.78 and −0.09 percent, respectively). Furthermore, there would be decreases in the prevalence of obesity and stroke under permanent DST, although to a lesser extent (−0.51 and −0.07 percent, respectively).

“We found that staying in Standard Time or staying in Daylight Saving Time is definitely better than switching twice a year,” Zeitzer said in a statement.

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