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Effects of Time Change: Fall Back, Leap Forward, Stroke Out?

TURKU, FINLAND – If you’ve noticed an uptick in stroke cases at your emergency department during mid-March, here’s a possible reason why: daylight saving time.

A new study to be presented at the American Academy of Neurology’s 68th Annual Meeting in Vancouver, Canada, next month finds that turning the clock ahead or back one hour appears to be linked to an increased risk of ischemic stroke, although the effect is only temporary.

“Previous studies have shown that disruptions in a person’s circadian rhythm, also called an internal body clock, increase the risk of ischemic stroke, so we wanted to find out if daylight saving time was putting people at risk,” explained study author Jori Ruuskanen, MD, PhD, of the University of Turku in Turku, Finland.

For the study, researchers reviewed a decade of data for stroke in Finland, comparing the rate of stroke in 3,033 patients hospitalized during the week following a daylight saving time transition to the rate of stroke in a group of 11,801 patients hospitalized either two weeks before or two weeks after that week.

Results indicate that the overall rate of ischemic stroke was 8% higher during the first two days after a daylight saving time transition. No difference was identified after two days, however.

The stroke risk increase was more pronounced in some groups, according to study authors. For example, cancer patients were 25% more likely to have a stroke after daylight saving time than during another period. The risk was also higher for older people: the over-65 cohort was 20% more likely to have a stroke right after the change in time.

On the other hand, the study found that hospital deaths from stroke did not increase in the week after a daylight saving time transition, even if stroke rates went up.

“Further studies must now be done to better understand the relationship between these transitions and stroke risk and to find out if there are ways to reduce that risk,” said Ruuskanen in an American Academy of Neurology press release.