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News / Health / Health Wire

Springing forward into daylight saving time can affect health

Circadian rhythm is forced to adjust itself

By LAURAN NEERGAARD, Associated Press
Published: March 9, 2024, 6:04am

WASHINGTON — Most of America will “spring forward” Sunday for daylight saving time. Losing that hour of sleep can do more than leave you tired and cranky the next day; it also could harm your health.

Darker mornings and more evening light together knock your body clock out of whack — which means daylight saving time can usher in sleep trouble. Studies have even found an uptick in heart attacks and strokes right after the March time change.

There are ways to ease the adjustment, including getting more sunshine to help reset your circadian rhythm for healthful sleep.

“Not unlike when one travels across many time zones, how long it can take is very different for different people,” said Dr. Eduardo Sanchez of the American Heart Association. “Understand that your body is transitioning.”

When does daylight saving time start? It begins at 2 a.m. Sunday, an hour of sleep vanishing in most of the U.S. The ritual will reverse on Nov. 3, when clocks “fall back” to standard time.

Hawaii and most of Arizona don’t make the spring switch, sticking to standard time all year, along with Puerto Rico, American Samoa, Guam and the U.S. Virgin Islands. Worldwide, dozens of countries also observe daylight saving time, starting and ending at different dates.

What happens to your brain when it’s lighter later? The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we’re more alert.

Morning light resets the rhythm. By evening, levels of a hormone called melatonin begin to surge, triggering drowsiness. Too much light in the evening — that extra hour from daylight saving time — delays that surge, and the cycle gets out of sync.

Sleep deprivation is linked to heart disease, cognitive decline, obesity and numerous other problems. And that circadian clock also influences things like heart rate, blood pressure, stress hormones and metabolism.

How does the time change affect your health? Fatal car crashes temporarily jump the first few days after the spring time change, according to a study of U.S. traffic fatalities. The risk was highest in the morning; researchers attributed it to sleep deprivation.

Then there’s the cardiac connection. The American Heart Association points to studies that suggest an uptick in heart attacks on the Monday after daylight saving time begins, and in strokes for two days afterward. (Doctors already know that heart attacks, especially severe ones, are a bit more common on Mondays generally — and in the morning.)