Daylight Saving Time may affect sleep at first, but it has a minor effect overall

For years, there has been a debate about the effects of Daylight Saving Time on health. Earlier research reported that the adverse effects of losing an hour of sleep included a spike in heart attacks, strokes, car accidents and mental health issues. But new research shows the time change is not as harmful as previously thought, said Miguel Prieto, MD, an internist with Cape Cod Healthcare’s Bourne Primary Care.

But, he acknowledged, the week after the change in the springtime clock can be rough.

“Regardless of what your position is, you cannot deny that when the clock changed on Sunday, for the first two days, you’re kind of tired,” he said. “It has to do with what we call circadian rhythm.”

To explain, Dr. Prieto identified three different clocks:

• The sun clock is basically like a sundial. Even if we change the time, the sundial does not change because that’s when the sun actually rises and sets.
• The social clock is identified by the time on your watch or clock. This may not necessarily match the sun clock.
• The biologic clock or circadian rhythm clock is the one that tells your body when to sleep. Whenever you change that, it is a little like the jet lag people experience when they travel. Dr. Prieto called that “social jet lag.”

New Research on Health Effects

New research has been debunking the older studies, said Dr. Prieto. In a recent study at Duke University Medical School, researchers looking at a meta-analysis study of 170,000 people over 10 years found no significant increase in heart attacks during the weeks surrounding Daylight Saving Time.

“They submitted that the actual rate of increase to be only 3 percent, which is statistically significant but it’s really clinically minor,” he said.

To explain why 3 percent is clinically minor, he used the example of looking at the odds of death over the next 10 years for a 50-year-old. Unless that person is participating in high-risk activities, that risk is probably 0.01 percent, he said. So, if the risk of death goes up 3 percent, the odds of death go up to 0.0103 percent. So, yes, it went up, but the absolute risk is still minor.

“All of these effects are transient, meaning they occur only in basically the first three days after the transition,” Dr. Prieto said. “And it’s the opposite in the fall when we bring the clocks back and you get an extra hour of sleep. That’s what they call the ‘fall back benefit.’”

The “fall back benefit” can be seen in another study of 690,000 participants from England over 10 years that was published in December 2025. Like the Duke study, the English study also showed that there is little evidence of a negative change in health events in the “spring ahead” period. But they did find there was a positive change in health events during the autumn “fall back” when people gain an extra hour of sleep. A week after the autumn change, research showed that there were fewer than expected cases of five health conditions, including anxiety, acute cardiovascular disease, depression, other psychiatric conditions, and sleep disorders.

The people that see the most negative outcomes of time changes are those who are in vulnerable populations, like the elderly and people who are already sleep deprived. If you are already sleep deprived, losing an extra hour will speed up the aging process, Dr. Prieto said.

How to Prepare Next Year

Some sleep specialists recommend “the 15-minute rule,” where you go to bed 15 minutes earlier for four nights before the spring change, but Dr. Prieto said that even when he tells patients this, they rarely actually do it. Even though it’s too late for this year, he has a better suggestion for next year.

“The main thing to do is wake up early and get the sunlight. When you get the sunlight for 30 minutes with exercise, what you will do is trigger your own brain’s release of melatonin when you go to sleep,” he said. “Melatonin is not a sedating substance. It is a chemical signal that your brain sends to the organs and then your organs go into hibernation mode, which happens overnight.”

When that hibernation occurs, all our biological functions slow down. We breathe slower and deeper, we don’t get hungry and we don’t tend to urinate as much. The combination of early exposure to light and exercise helps stabilize circadian rhythms to help us adjust quicker to the time change, Dr. Prieto said.