October 30, 2008

Turning Back Clock Has Benefits For Heart

New research shows that turning back the clock one hour for daylight savings time may actually be good for your heart. 

The Swedish study found that while adjusting clocks forward one hour during spring increases the risk of myocardial infarction in the following week, setting them back during fall reduces the risk, albeit to a lesser extent.

The researchers examined records dating back to 1987 and found that the number of heart attacks went down on the Monday after clocks were turned back, possibly because people got an extra hour of sleep. In contrast, they found that the average number of heart attacks increased by about five percent during the first week of summer time, possibly due to sleep deprivation from the lost hour of sleep.

"Our data suggest that vulnerable people might benefit from avoiding sudden changes in their biologic rhythms," Drs. Imre Janszky of the Karolinska Institute and Rickard Ljung of the National Board of Health and Welfare told Reuters. 

"There's a small increase in risk for the individual, especially during the first three days of the new week," said Dr Janszky.

"The disruption in the chronobiological rhythms, the loss of one hour's sleep and the resulting sleep disturbance are the probable causes."

According to the scientists, the study provides a conceivable explanation for why myocardial infarction is most common on Mondays, as shown by previous research.

"It's always been thought that it's mainly due to an increase in stress ahead of the new working week," said Dr Janszky.

"But perhaps it's also got something to do with the sleep disruption caused by the change in diurnal rhythm at the weekend."

"The earlier wake-up times on the first workday of the week and the consequent minor sleep deprivation can be hypothesized to have an adverse cardiovascular effect on some people. This effect would be less pronounced with the transition out of daylight saving time, since it allows for additional sleep," the scientists wrote in a letter to the New England Journal of Medicine.

However, the protective effect seen in autumn may last for as little as one day because, "Monday is the day when most of us will use this extra hour," Janszky told Reuters.

The researchers found that women were more vulnerable than men to heart attacks during the spring shift to daylight saving time, and men were more likely to be protected during the Monday in the autumn.  They also found the effect was more distinct in those under the age of 65, something Janszky attributes to less flexible schedules among younger people.

"Retired people are more independent from the official time," he said.

Even though the increase and decrease in risk are relatively small for the individual, the team believes that the study can improve our understanding of how disruptions to diurnal rhythms impact on our health.

"Roughly 1.5 billion people are subjected to these clock-shifts every year, but it's hard to make any generalized statement about how many heart attacks they can cause," adds Dr Rickard Ljung, another member of the research team.


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