prior blog entry, it was discussed how sleep deprivation on the Monday following a shift to spring daylight savings time results in a small increase in fatal car accidents.
A new study reported in a recent issue of the American Journal of Cardiology provided evidence to show that daylight savings time shifts might briefly and modestly affect the incidence and type of acute (sudden) heart attacks.
In the study mentioned above, there were 935 patients (59% men and 41% women) whose electronic medical records were reviewed at two emergency centers in Michigan. The researchers studied the incidence of sudden heart attacks that presented to the hospital the week after daylight savings time and after the autumn switch to standard time. There were 328 patients studied during that time frame. A comparison group was also studied, made up of 607 patients with comparable diagnoses who came to the hospital two weeks before and two weeks after the shift to daylight savings time.
The main finding that reached statistical significance was an increase in a type of heart attack after the transition to daylight savings time compared to patients who were studied two weeks before and after the shift to daylights savings time. This was noted for the first day (Sunday) after the transition to Spring.
The increased heart attack risk is theorized to because of the biological effects of decreased sleep length and sleep quality. For example, partial night sleep deprivation is associated with increased levels of certain chemical related to cardiac function such as norepinephrine. It can also increase the rate of firing of nerve cells that regulate heart rate. Increased blood pressure and narrowing of blood vessels was suggested as another possible cause of acute heart attack after sleep deprivation.
While the results of this study are interesting, they cannot definitely prove that transition to daylight savings time causes acute heart attacks because it is based in a retrospective chart review (preventing the researchers from controlling other factors that could influence the results), is based on association (associations do not prove causation), and because there were not enough heart attacks per day to strengthen the power of the statistical analyses. More research is still needed to determine if the increased risk indicated in this study is real and if so, how to decrease the risk. Until that time, common sense would indicate that trying to get extra sleep during the daylight savings time transition is a smart thing to do, especially if you have risk factors for heart disease.
Suggested reading: Mayo Clinic Healthy Heart for Life!
Reference: Jiddou MR, Pica M, Boura J, Qu L, Franklin BA.(2013). Incidence of myocardial infarction with shifts to and from daylight savings time. Am J Cardiol., 111(5):631-5.