Swedish researchers have seen at 20 years of records and invented that the number of heart attacks dipped on the Monday after clocks were set back an hour, possibly because people got an extra hour of sleep.
But moving clocks forward in the spring appeared to have the opposite effect. There were more heart attacks during the week after the start of daylight saving time, particularly on the first three days of the week.
"Sleep - through a variety of mechanisms - affects our cardiovascular health," said Dr. Lori Mosca, director of preventive cardiology at New York-Presbyterian Hospital, who was not involved in the research. The findings show that "sleep not only impacts how we feel, but it may also affect whether we develop heart disease or not."
Overall, in the week after "spring forward," there was a 5 percent increase in heart attacks, with a 6 percent bump on Monday and Wednesday and a 10 percent increase on Tuesday. In the week after "fall back," the number of heart attacks was about the same, except on Monday, which had a 5 percent decrease.
"The finding that the possibility of additional sleep seems to be protective on the first workday after the autumn shift is intriguing," the authors wrote.
Doctors have long known that Monday in general is the worst day for heart attacks, and they usually blame the stress of a new work week and increased activity. The Swedish researchers said their findings suggest that the minor loss of sleep that occurs at the end of ordinary weekends - with people going to bed later on Sunday and getting up early on Monday - might also be a contributing factor.
Last year, a study by American researchers found there were more pedestrian deaths during the evening rush hour in November than October as drivers and pedestrians adjust to the earlier darkness. They said the risk for pedestrians drops in the morning when clocks are set back and daylight comes earlier.
Daylight saving time in the United States ends this year at 2 a.m. Sunday. All states except Arizona and Hawaii will make the switch. Sweden and the rest of Europe turned back their clocks last weekend. More than 1.5 billion people worldwide live in countries that use daylight saving time, the researchers said.
Sleep can affect the heart through changes in blood pressure, inflammation, blood clotting, blood sugar, cholesterol and blood vessels, Mosca said. She suggested that anxiety from changes in routine may also be a factor, in addition to loss of sleep.
Dr. Ronald Chervin, director of the University of Michigan's Sleep Disorders Center, said this is a "sleep-deprived society," and he advises taking advantage of Sunday's time change and getting an extra hour of sleep.
In the spring, he suggests gradually adjusting to the one-hour loss by going to bed and getting up 15 minutes earlier for a few days before the time change.
"We spend a third of our lives sleeping and people forget how much effect it has on overall health," he said.
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