Adjusting the clocks to summer time on the last Sunday in March increases the risk of myocardial infarction in the following week. In return, putting the clocks back in the fall reduces the risk, although to a lesser extent, according to a new Swedish study.
Scientists at Karolinska Institutet have examined how the incidence of myocardial infarction changes with the summer and fall clock-shifts since 1987. Their results show that the number of heart attacks, on average, increases by about five per cent during the first week of summer time.
“There’s a small increase in risk for the individual, especially during the first three days of the new week,” says Dr. Imre Janszky, one of the researchers behind the study. “The disruption in the chronobiological rhythms, the loss of one hour’s sleep and the resulting sleep disturbance are the probable causes.”
The team also observed that the readjustment back to fall time on the last Sunday in October, which allows for an extra hour of sleep, is followed by a reduction in the risk of heart attack on the following Monday.
The reduction for the whole week, however, is less than the increase related to the summer time adjustment. According to the scientists, the study provides a possible explanation for why myocardial infarction is most common on Mondays, as indicated by previous research.
“It’s always been thought that it’s mainly due to an increase in stress ahead of the new working week,” says Janszky. “But perhaps it’s also got something to do with the sleep disruption caused by the change in diurnal rhythm at the weekend.”
Although the increase and decrease in risk are relatively small for the individual, the research team believes that the study can improve our understanding of how disruptions to diurnal rhythms adversely affect 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,” says Dr Rickard Ljung, a study co-author.
Many individuals claim that daylight saving time disrupts their sleeping patterns and natural body clocks. Stress, headaches and drowsiness are a few of the effects of the daylight savings time clock-shifts that may occur. Exercise, such as walking or running, can aid in reducing fatigue.
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