Daylight saving time linked to heart attacks: study

WASHINGTON Sat Mar 29, 2014 10:39am EDT

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WASHINGTON (Reuters) - 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 cycles.

"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 week.

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 said.

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 needed.

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 intervention.

(Reporting by Ransdell Pierson; Editing by James Dalgleish)

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Comments (8)
markavelli69 wrote:
This sounds a lot like climate science. They draw a big conclusion from a very narrow study.
They looked @ Michigan hospitals only. The studied hospital patients only. They studied them for 4 years only. Then draw a nation wide conclusion for all people…go figure.

Mar 29, 2014 11:20am EDT  --  Report as abuse
catalinda8 wrote:
There are so many studies with so many statitics that they have become meaningless. Basically, on any given day, there may be some factor that causes some sort of fluctuation in the health of some people. I doubt most people get exactly the same amount of sleep every night – so seriously, losing one hour (if they’re not smart enough to go to bed an hour earlier) is really responsible? This is getting ridiculous. And these researchers wonder why no one listens anymore!

Mar 29, 2014 11:40am EDT  --  Report as abuse
promytius1 wrote:
25% of what? You can’t dissect a study like that. 42,000 cases and on one data point there was an indistinguishable rise in one data set. The difference between 42,000/32 and 42,000/40 is not statistically significant. You can’t rip data apart like that with any validity.

Mar 29, 2014 11:41am EDT  --  Report as abuse
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