| WASHINGTON, March 29
WASHINGTON, March 29 Switching over to daylight
saving time, and losing one hour of sleep, raised the risk of
having a heart attack the following Monday by 25 percent,
compared to other Mondays during the year, according to a new
U.S. study released on Saturday.
By contrast, heart attack risk fell 21 percent later in the
year, on the Tuesday after the clock was returned to standard
time, and people got an extra hour's sleep.
The not-so-subtle impact of moving the clock forward and
backward was seen in a comparison of hospital admissions from a
database of non-federal Michigan hospitals. It examined
admissions before the start of daylight saving time and the
Monday immediately after, for four consecutive years.
In general, heart attacks historically occur most often on
Monday mornings, maybe due to the stress of starting a new work
week and inherent changes in our sleep-wake cycle, said Dr.
Amneet Sandhu, a cardiology fellow at the University of Colorado
in Denver who led the study.
"With daylight saving time, all of this is compounded by one
less hour of sleep," said Sandhu, who presented his findings at
the annual scientific sessions of the American College of
Cardiology in Washington.
A link between lack of sleep and heart attacks has been seen
in previous studies. But Sandhu said experts still don't have a
clear understanding of why people are so sensitive to sleep-wake
"Our study suggests that sudden, even small changes in sleep
could have detrimental effects," he said.
Sandhu examined about 42,000 hospital admissions in
Michigan, and found that an average of 32 patients had heart
attacks on any given Monday. But on the Monday immediately after
springing the clock forward, there were an average of eight
additional heart attacks, he said.
The overall number of heart attacks for the full week after
daylight saving time didn't change, just the number on that
first Monday. The number then dropped off the other days of the
People who are already vulnerable to heart disease may be at
greater risk right after sudden time changes, said Sandhu, who
added that hospital staffing should perhaps be increased on the
Monday after clocks are set forward.
"If we can identify days when there may be surges in heart
attacks, we can be ready to better care for our patients," he
The clock typically moves ahead in the spring, so that
evenings have more daylight and mornings have less, and returns
to standard time in the fall. Daylight saving time was widely
adopted during World War I to save energy, but some critics have
questioned whether it really does so and whether it is still
Researchers cited limitations to the study, noting it was
restricted to one state and heart attacks that required
artery-opening procedures, such as stents. The study therefore
excluded patients who died prior to hospital admission or
(Reporting by Ransdell Pierson; Editing by James Dalgleish)