September 19, 2025, 11:02 am | Read time: 4 minutes
In 70 countries worldwide, the time is still changed twice a year. This continues despite the well-known fact that this measure is not beneficial to health. Many people feel exhausted around the time change, and studies show an increased risk of various health problems. A recent study has shown how significantly many strokes could be prevented by abolishing the time change. The same applies to cases of obesity.
Abolishing the Time Change, 300,000 Fewer Strokes?
We are currently still in daylight saving time—a German invention that was adopted by many countries. The goal was to use sunlight more effectively and thus require less energy. However, the benefit soon proved to be limited. Meanwhile, the negative effects of the time change on the biological clock are also known. Yet, discussions about abolishing the controversial routine continue. A new study from Stanford Medicine—so far, only a press release has been published—once again provides arguments for finally taking action.1 Specifically: concrete numbers. According to the study, abolishing the time change in the U.S. could prevent 300,000 strokes and 2.6 million cases of obesity each year.
Details of the Study
The researchers examined the potential long-term effects of different time regulations on health. They studied three possible models:
- a permanent standard time (this would be the so-called “winter time”)
- a permanent daylight saving time
- the current scenario with a biannual time change
The focus of their study was on how these variants affect the circadian rhythm. This so-called internal clock of humans is known to control numerous biological processes, including the immune system and the sleep-wake cycle. It is known that sleep problems can increase the risk of stroke. It is further known that sleep affects hormone balance, metabolism, and eating behavior, and is therefore also related to body weight.
The researchers developed a mathematical model to calculate how much the natural biorhythm shifts when people live under different time systems. This model included local sunrise and sunset times, the geographical location of individual regions, and data on the population’s health status. They then linked the determined circadian stresses (biorhythm changes) with specific disease data, including data from the U.S. Centers for Disease Control and Prevention (CDC). They focused on diseases that are demonstrably closely related to disruptions of the biorhythm, including strokes, obesity, depression, and cardiovascular diseases.
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Measurable Effects of a Disrupted Sleep-Wake Rhythm
When comparing the three time regulations, the current system, with a biannual change, performed the worst. From a health perspective, it would be best to permanently maintain standard time. According to the calculations, this could prevent around 300,000 strokes and 2.6 million cases of obesity annually in the U.S. Even a permanent switch to daylight saving time would still be a better option compared to the constant change, according to the researchers.
In summary, they clearly advocate for completely abolishing the time change and permanently maintaining standard time—at least from a health perspective. However, they emphasize that this decision cannot be made based solely on biological factors. Economic and social aspects must also be considered. An important addition, as also highlighted in the conversation with Dr. Feld.
Why the “Unhealthy” Time Change Is Still Maintained
The expert is unimpressed by the new study results. Not least because there is an opinion from the scientific service of the EU Commission, which officially proposed ending the seasonal change in 2018.2 The connections between heart attacks around the switch to daylight saving time and strokes, which he mentioned above, are clearly proven. After the time change in winter, the rates decrease again. This is explained, among other things, by the increased likelihood of platelet (thrombocyte) clumping in the morning. Referring to a study from 2011, he emphasizes that this is a natural process that prepares the body for the day.3 For example, to stop bleeding if injured. During daylight saving time, it is darker in the morning, resulting in less natural light, which means waking up contrary to the internal clock. This discrepancy can further increase platelet activity and thus the risk of strokes.
So why hasn’t the time change been abolished yet? “I believe the main reason is the fear of a system collapse,” he explains. In all major data centers, corporations, and even in cars, the time is intricately synchronized. Dr. Feld recalls the turn of the millennium in 1999/2000. At that time, a major disaster was feared—that systems would supposedly not cope with the time change.
Strokes, like obesity, are serious health threats. Given the growing evidence of the risks of the time change, the question arises whether these should finally be weighed more seriously against the feared technical and organizational problems.