Changing the clock twice a year could put 300,000 Americans at risk each year of a potentially fatal stroke.
A new study, conducted by Stanford Medicine researchers, found that switching between Daylight Saving Time (DST) and Standard Time (SDT) disrupts the body's internal clock by forcing it to adapt too frequently to changes in light and darkness.
Daylight Saving Time is when clocks are moved forward one hour in the spring to allow for more light in the evenings and back one hour in the fall to restore Standard Time.
The next change is scheduled for November 2, 2025, at 2 a.m. in each time zone.
However, scientists found that this disruption weakens the circadian rhythm – the body's internal 24-hour clock that relies on morning light to regulate bodily functions and stay healthy.
While simulating what would happen if the US decided to permanently keep Standard Time after the “return” in November, estimates showed that the change could prevent about 300,000 strokes each year by reducing this circadian load.
The switch to permanent Daylight Saving Time was less effective because it prioritized evening light over morning light, but it still prevented about 220,000 strikes compared to resetting the clocks every few months.
Dr. Jamie Zeitzer, professor of psychiatry and behavioral sciences, said:
“Staying on standard time or daylight saving time is definitely better than switching twice a year.”
Stroke occurs when blood flow to the brain is blocked or a blood vessel ruptures, damaging brain cells and potentially causing death.
According to the CDC, about 795,000 strokes occur each year in the U.S., with 185,000 of them fatal.
The strain that the time change places on the circadian rhythm can lead to stroke by increasing blood pressure and inflammation in the brain.
As sudden one-hour shifts force the internal clock to adjust unnaturally, the body struggles to maintain its natural processes, especially when exposure to light in the morning and evening is erratic.
Zeitzer and study co-author Lara Weed, a doctoral student in bioengineering, found that this mismatch causes an ever-increasing “circadian load” each year.
Circadian workload refers to the total amount of adaptation that the body's internal 24-hour clock must endure to synchronize with a person's daily rhythm, such as work or school schedules.
This load was measured hourly over the course of a year and showed how much the body's natural clock had to adjust to match social life.
The twice-yearly (BAS) switch added the most workload (21 hours), compared to permanent Standard Time (18.5 hours) or permanent Daylight Saving Time (19.6 hours).
"The more light exposure you have at the wrong times, the weaker the circadian clock becomes. And everything that comes after that – for example, the immune system, energy – is no longer aligned properly," Zeitzer explained in a university news release.
The study also found that banning clock changes could reduce obesity rates, averting 2.6 million cases if the country maintained Standard Time and 1.7 million cases under permanent Daylight Saving Time.
However, the findings, published in the journal Proceedings of the National Academy of Sciences, highlighted that there was no apparent link between the policies of the time and other diseases such as arthritis, cancer, heart disease or depression.
This is not the first study to warn about the impact that changing the clock twice a year has on the human body.
Earlier this year, leading scientists in the UK called for an end to Daylight Saving Time, amid fears that it is fuelling increases in cancer cases, road accidents and suicide attempts.
A statement from the British Sleep Society highlighted some of the worrying effects of the clock change.
Losing an hour of sleep when the clocks are moved forward in the spring results in the population feeling more tired than usual.
Some studies have suggested that the risk of fatal road accidents increases by about six percent after the spring transition to Daylight Saving Time.
British researchers also found evidence of an increased risk of cardiovascular events, an increased risk of suicidal behavior, and increased mortality in the days immediately following the clock change. /GazetaExpress/
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