A new research, based on heart attacks in Sweden, shows that sleep deprivation may be directly linked to an increased risk of heart attack. Swedish researchers have found an increase in the number on heart attacks following the springtime shift for the start of daylight saving time and a decrease in heart attack rates on autumn, when the clocks go back and we all get an extra hour for our beauty sleep.

According to the study, conducted by researchers at the Karolinska Institute in Stockholm and published in the New England Journal of Medicine, after the world has set their clock one hour forward this year the rate of heart attacks dropped with 5%. Scientists suggest one possible explanation: the adverse effect of sleep deprivation on cardiovascular health. Sleep deprivation has negative consequences on our heart: it boosts blood pressure and heart rate, which can lead to a tendency to form dangerous clots.  

“Our data suggest that vulnerable people might benefit from avoiding sudden changes in their biologic rhythms,” said Imre Janszky of the Karolinska Institute and Rickard Ljung of the National Board of Health and Welfare, Stockholm. Previous studies have shown that problems of disruptions of the biological rhytm and sleep problems are connected to cardiovascular health, Janszky said.

The researchers looked at data on heart attacks for a period of 20 years between 1987 and 2006. They calculated the number of heart attacks a few weeks before and after the days when the clocks were changed and made a comparison between the average rates of heart attacks on those days.

In the week after “spring forward,” there was a 5 percent increase in heart attacks, with a 6 percent bump on Monday and Wednesday and a 10 percent increase on Tuesday. The effect was more pronounced in women. In the week after “fall back,” a significant increase was seen only on the first weekday after the transition and the effect was more pronounced in men. The effect was more pronounced in people under age 65 on both seasons.

Monday is the day of the week associated with the highest risk of attacks because of the mental stress of starting a new work week and the increase in activity, the researchers said. The shift may affect working people more because they have to stick to their program, while those who are retired have a more flexible schedule.

More than 1.5 billion people turn their clocks forward in the spring and backward in the fall. The lack of sleep associated with the springtime shift may affect people, adding an increased risk for several heart attack risk factors including high blood pressure, inflammation and obesity. The study adds another element on the list of risk factors for cardiovascular disease, but other researchers say changing the clock is just a minor factor compared to smoking and overeating.