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Science Says: How daylight saving time affects health

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Published: October 31, 2019, 2:45pm

Office workers bemoan driving home in the dark. Night owls relish the chance to sleep in. As clocks tick toward the end of daylight saving time, many sleep scientists and circadian biologists are pushing for a permanent ban because of potential ill effects on human health.

Losing an hour of afternoon daylight sounds like a gloomy preview for the dark winter months, and at least one study found an increase in people seeking help for depression after turning the clocks back to standard time in November — in Scandinavia. Research shows the springtime start of daylight saving time may be more harmful, linking it with more car accidents, heart attacks in vulnerable people and other health problems that may persist throughout the time change.

Here’s what science has to say about a twice-yearly ritual affecting nearly 2 billion people worldwide.

• SLEEP EFFECTS

Time changes mess with sleep schedules, a potential problem when so many people are already sleep deprived, says Dr. Phyllis Zee, a sleep researcher at Northwestern Medicine in Chicago.

About 1 in 3 U.S. adults sleep less than the recommended seven-plus hours nightly, and more than half of U.S. teens don’t get the recommended eight-plus hours on weeknights. One U.S. study found that in the week following the spring switch to daylight saving time, teens slept about 2 1/2 hours less than the previous week. Many people never catch up during the subsequent six months.

Local angle

Gov. Jay Inslee signed a bill earlier this year to make daylight saving time permanent in Washington. And while Oregon and California also passed similar legislation, Congress must approve the change for it to take effect. The idea has not yet received a congressional hearing, so West Coast residents will still need to set their clocks back an hour Sunday.

Research suggests that chronic sleep deprivation can increase levels of stress hormones that boost heart rate and blood pressure, and of chemicals that trigger inflammation.

• HEART PROBLEMS

It has also been shown that blood tends to clot more quickly in the morning. These changes underlie evidence that heart attacks are more common in general in the morning, and may explain studies showing that rates increase slightly on Mondays after clocks are moved forward in the spring, when people typically rise an hour earlier than normal.

That increased risk associated with the time change is mainly in people already vulnerable because of existing heart disease, said Barry Franklin, director of preventive cardiology and cardiac rehabilitation at Beaumont Health hospital in Royal Oak, Mich.

Studies suggest that these people return to their baseline risk after the autumn time change.

• CAR CRASHES

Numerous studies have linked the start of daylight saving time in the spring with a brief spike in car accidents, and with poor performance on tests of alertness, both likely due to sleep loss.

The research includes a German study published this year that found an increase in traffic fatalities in the week after the start of daylight saving time, but no such increase in the fall.

Other studies on how returning to standard time in the fall might impact car crashes have had conflicting results.

• OUR INTERNAL CLOCKS

Circadian biologists believe ill health effects from daylight saving time result from a mismatch among the sun “clock,” our social clock — work and school schedules — and the body’s internal 24-hour body clock.

Ticking away at the molecular level, the biological clock is entrained — or set — by exposure to sunlight and darkness. It regulates bodily functions such as metabolism, blood pressure and hormones that promote sleep and alertness.

Disruptions to the body clock have been linked with obesity, depression, diabetes, heart problems and other conditions.

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