Daylight Saving Time May Affect Heart
Study Shows Fewer Heart Attacks When Clocks Are Moved Back
Oct. 29, 2008 -- This weekend brings an end to daylight saving time, and if
you're lucky enough to get an extra hour of sleep when you turn your clock
back Saturday night, a new study suggests that it might save your life.
When researchers in Sweden examined the impact of daylight saving time on heart attack rates in that
country, they discovered that people had slightly fewer heart attacks on the
Monday after they set their clocks back in the fall and slightly more heart
attacks in the days after they set their clocks ahead in the spring.
They presented their findings in a letter published in the Oct. 30 issue of
The New England Journal of Medicine.
Study co-author Rickard Ljung, MD, PhD, says the results suggest that even
small disturbances in sleep patterns may affect the heart.
"We know that Monday is the most dangerous day for heart attacks,"
he tells WebMD. "It has been thought that this is due to the stress associated with returning to work after the
weekend, but our study suggests that disturbed sleep rhythms may be involved,
and that the extra hour of sleep we get in the fall [after daylight saving time
ends] may be protective."
Spring Forward, Fall Back
Ljung and colleague Imre Janszky, MD, PhD, of Stockholm's Karolinska
Institute compared heart attack rates in Sweden between 1987 and 2006 in the
week following daylight saving time to heart attack rates two weeks before and
two weeks after the spring and fall events using a comprehensive national
They discovered a 5% increase in heart attacks in the first three workdays
after clocks were set ahead for the beginning of daylight saving time in the
spring and a similar decrease on the Monday after clocks were set back for the
end of daylight saving time in the fall.
"That is not a big difference, but it was significant," Ljung says.
It also may translate into sizeable numbers of individuals in absolute terms,
given that 1.5 billion people are affected by daylight saving time shifts
across the globe.
The effect of the spring transition to daylight saving time on heart attack
rates was slightly greater for women than men, and the fall effect was more
pronounced in men than in women. And the effect was consistently more
pronounced in people under age 65 than for those 65 and older.
Recent research links sleep deprivation to an increased risk for several
heart attack risk factors including high blood pressure,
inflammation, and obesity.
Northwestern University professor of preventive medicine Martha Daviglus,
MD, says there is growing evidence that chronic sleep deprivation has a
negative impact on the heart. But she is less convinced of the impact of
isolated events like daylight saving time.
"I wouldn't want people to get the idea that losing one hour of sleep
will cause them to have a heart attack," she says.