Daylight Saving Time Tied to Spike in Stroke Risk
But overall increase was only 8 percent higher in the first two days after a clock change, researchers said
By Amy Norton
MONDAY, Feb. 29, 2016 (HealthDay News) -- Changing the clocks for daylight saving time may cause a short-lived spike in some people's risk of suffering a stroke, a preliminary study hints.
Looking at a decade's worth of stroke data, Finnish researchers found that the national incidence of stroke tended to rise slightly over the two days following daylight saving time transitions -- whether the clocks were turned forward or back.
The findings do not prove that daylight saving time is to blame.
On the other hand, it's hard to imagine other factors that would explain such a specific pattern, said researcher Dr. Jori Ruuskanen, a neurologist at Turku University Hospital.
Plus, he said, there is a known link between disruptions in the body's circadian rhythms and stroke risk. Circadian rhythms refer to the shifts in the body's biological processes that happen over 24 hours -- largely in response to light and darkness.
Those rhythms can be thrown off in different ways, Ruuskanen said. Shift work and insomnia are two examples, he noted, and both have been tied to increased risks of health conditions, including stroke.
Ruuskanen is scheduled to present the findings in April at the American Academy of Neurology's annual meeting in Vancouver, Canada. Research presented at meetings is considered preliminary until published in a peer-reviewed medical journal.
Dr. Andrew Lim is a neurologist at Sunnybrook Health Sciences Center, in Toronto, who studies sleep and circadian rhythms. He agreed that daylight saving time could plausibly affect stroke risk.
"Sleep is associated with many physiological changes that are normally thought of as being relatively protective against stroke, like lower blood pressure," explained Lim, who was not involved in the new study.
When sleep is disrupted, he said, there may also be shifts in those protective biological processes.
For the study, Ruuskanen's team looked at Finnish stroke figures for the years 2004 to 2013. The investigators then compared just over 3,000 people who'd been hospitalized for an ischemic stroke during the week after a daylight saving transition with nearly 12,000 people who'd suffered a stroke in the two weeks before or after a transition week.