Permanent Standard Time Could Cut Strokes, Obesity Among Americans

A new Stanford-led study finds that switching permanently to standard time could prevent 300,000 strokes and reduce obesity in 2.6 million Americans by better aligning circadian rhythms with natural light. Researchers argue that the twice-yearly clock changes are the worst option for public health, while permanent daylight saving time would offer two-thirds of the benefits. From a report: 'We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year,' senior researcher Jamie Zeitzer said in a news release. He's a professor of psychiatry and behavioral sciences at Stanford University in California. For the study, researchers estimated how different national time policies might affect American's circadian rhythms -- the body's innate clock that regulates many physiological processes. The human circadian cycle isn't exactly 24 hours, researchers noted. It's about 12 minutes longer for most people, and it can be changed based on a person's exposure to light.

'When you get light in the morning, it speeds up the circadian cycle. When you get light in the evening, it slows things down,' Zeitzer said. 'You generally need more morning light and less evening light to keep well synchronized to a 24-hour day.' An out-of-sync circadian cycle has been linked with many different poor health outcomes, researchers said. 'The more light exposure you get at the wrong times, the weaker the circadian clock,' Zeitzer said. 'All of these things that are downstream -- for example, your immune system, your energy -- don't match up quite as well.' Most people would experience the least circadian burden under permanent standard time, which prioritizes morning light, researchers found.

The research team then linked its analysis of circadian rhythms to county-level data from the U.S. Centers for Disease Control and Prevention (CDC) to see how each time policy might affect people's health. Their models showed that permanent standard time would reduce obesity nationwide by 0.78% and stroke by 0.09%. Those seemingly small percentage changes, when played out across the national population, would mean 2.6 million fewer people with obesity and 300,000 fewer cases of stroke. Permanent daylight savings time would result in a 0.51% drop in obesity -- around 1.7 million people -- and a 0.04% reduction in strokes, or 220,000 cases. Either move would help American health. 'You have people who are passionate on both sides of this, and they have very different arguments,' Zeitzer said. The findings have been published in the Proceedings of the National Academy of Sciences.

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