Swedish researchers have found a jump in the number of heart attacks following the semi-annual one-hour time changes in many Northern hemisphere countries.
"This was the very first study on this topic and further studies are needed," said Dr Imre Janszky, of the Karolinska Institute in Stockholm, and co-author of a letter published in the October 30 issue of the New England Journal of Medicine.
Avoid sudden changes
"However, we can certainly say that our study adds some further evidence that vulnerable individuals might benefit from avoiding sudden changes in their biological rhythms," Janszky said.
Those vulnerable individuals would include people already sleep deprived, other experts said.
"When somebody has sleep deprivation, obviously that deprivation does affect their health, including the possibility of having heart attack and stroke," said Susan Zafarlotfi, clinical director of the Institute for Sleep-Wake Disorders at Hackensack University Medical Centre in New Jersey. "Those patients who do have a higher risk - such as high cholesterol and, specifically, if they snore - should be very, very careful with their time to bed and time to rise, not only for the fall back, but also across the board."
Cues from time and light
"Our circadian rhythm, which is the biological clock within the human body, gets its cues from time and light," Zafarlotfi explained. "This coming Sunday when we (the US) go backwards, our bodies are not going to be clocking so quickly, so the clinical consequences would be fatigue, tiredness and a little bit of lack of attention and lack of concentration."
For the new research, the study authors used a registry with information on all heart attacks occurring in Sweden since 1987. Then they compared how many heart attacks happened during each of the first seven days after "spring forward" and "fall back," and the average of how many occurred on the corresponding weekdays two weeks before and two weeks after the day of transition.
There was a spike in heart attacks for the first three weekdays after the change to daylight saving time in the spring, an effect that was more pronounced in women. In the fall, there was a slight drop in the number of heart attacks on the Monday after the transition, but more heart attacks by the time the following Friday rolled around; this effect was more pronounced in men, the researchers found.
Regardless of the time of year, the effects tended to be stronger for people younger than 65 than for those over 65.
Sleep deprivation blamed
The study authors hypothesised that the increase in risk was likely due to the negative effects of sleep deprivation on heart health.
The next step in the research would be to see if prolonged sleep might reverse the problem, especially given that people in western societies tend to lack sleep. Their average night's rest has decreased from 9 hours to 7.5 hours during the last century. – (HealthDayNews)