By Lindsey Tanner
Office workers bemoan driving home in the dark. Night owls relish the chance to sleep in. As clocks were turned back an hour with the end of daylight saving time Sunday morning, 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.
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.
One U.S. study found that in the week following the spring switch to daylight saving time, teens slept about 21/2 hours less than the previous week. Many people never catch up during the subsequent six months.
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.
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.
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.
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.
Disruptions to the body clock have been linked with obesity, depression, diabetes, heart problems and other conditions. Circadian biologists say these disruptions include tinkering with standard time by moving the clock ahead one hour in the spring.
PRESSURE TO CHANGE
In the U.S., daylight saving time runs from the second Sunday in March to the first Sunday in November. It was first established 100 years ago to save energy. Modern-day research has found little or no such cost savings.
Federal law allows states to remain on standard time year-round but only Hawaii and most of Arizona have chosen to. Proposed legislation in several states would have them join suit—or switch to year-round daylight saving time, which would require congressional approval.
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