Our bodies run on a natural 24-hour cycle known as the circadian rhythm.
This internal clock governs sleep, appetite, body temperature, and alertness throughout the day.
When we change the time, even by an hour, this delicate rhythm is disrupted, and the effects can ripple through our health in surprising ways.
A study published in Proceedings of the National Academy of Sciences in October 2025, conducted by Lara Weed and Professor Jamie Zeitzer from Stanford University, found that adjusting the clock twice a year increases the risk of both stroke and obesity.
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The disruption may seem small, but over time it weakens the body’s ability to maintain essential biological balance.
Why switching time takes a toll
The transition to daylight saving time each spring means losing an hour of sleep, and research found a noticeable spike in heart attacks and traffic accidents during the days that follow.
According to the study, the long-term impact of switching time twice a year is even more concerning.
The researchers compared three systems: permanent standard time, permanent daylight saving time, and the current model that alternates between the two.
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The results were clear that the current system was the worst for public health.
Constantly forcing the body to readjust its internal clock can lead to chronic fatigue, higher stress levels, and metabolic disturbances linked to heart disease and obesity.
Why standard time works best
Our bodies function best when exposed to bright light in the morning and dim light in the evening, explains Professor Jamie Zeitzer of Stanford University.
When light exposure happens at the wrong time of day, it weakens the circadian rhythm.
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Using mathematical models, Jamie Zeitzer and his team studied how light exposure affects people throughout the year.
Their conclusion was that most individuals would be healthier if we stayed on standard time permanently.
Interestingly, about 15 percent of people, often early risers, might adapt better to permanent daylight saving time, as their biological clocks are more tolerant of evening light.
Sources: Netdoktor.dk, and Proceedings of the National Academy of Sciences
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