Original ArticleDaylight saving time shifts and incidence of acute myocardial infarction – Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA)
Introduction
Use of daylight saving time (DST) is common in mid- and high-latitude countries. More than 1.5 billion men and women are exposed to the practice of turning clocks forward or backward by an hour in spring and in autumn, respectively. Clock shifts may disrupt chronobiological rhythms, influence sleep duration and quality, and the effect lasts for several days after the DST change [1], [2], [3].
We have previously found that, after the springtime shift into DST, there is a modest increase in acute myocardial infarction (AMI) incidence which lasts for several days. Overall, the relative risk increase for the first week is 5%. In contrast, AMI incidence was only decreased on the first weekday after the transition out of DST in the autumn. The most plausible explanation for this findings was the adverse effect of sleep deprivation and circadian misalignment on cardiovascular health [4]. In this previous work, which was based on the national Swedish Myocardial Infarction Register [5], we were limited to investigating age and sex as factors that might influence how DST shifts influence risk of AMI. However, several established risk factors for AMI have been shown to be associated with sleep or circadian habits, including smoking, lipids, body mass index, diabetes, or blood pressure [6], [7], [8], [9], [10], [11]. Thus, there are plausible reasons to expect considerable variation between individuals in their vulnerability to clock shifts that we were previously unable to address. If such variations between individuals were identified, then our understanding of mechanisms of the acute cardiovascular effects of sleep deprivation or circadian misalignment might be advanced, which could eventually lead to better preventive strategies.
Therefore, in the present study, which was based on the Register of Information and Knowledge about Swedish Heart Intensive Care Admissions (RIKS-HIA), we sought to confirm our original findings on changes in risk associated with DST and to investigate the role of individual factors including age, sex, history of cardiac events, diabetes, hypertension, smoking, BMI, lipids, and medication in enhancing or mitigating the risks associated with DST.
Section snippets
Methods
RIKS-HIA registers all patients admitted to the coronary care units of participating hospitals (see http://www.riks-hia.se for more information) [12], [13], [14], [15]. It started with 19 participating hospitals in 1995. The last year available with quality checked data for the current analyses was 2007, when 74 hospitals participated, covering over 95% of coronary care admissions in Sweden. In our analyses we included all available patients with a diagnosis of AMI. The criteria for the
Transition into DST
Table 1 shows the expected and observed incidence of AMI and incidence ratios with 95% confidence intervals on the first week after the spring clock shift. Overall, we found a slightly elevated incidence for the first week after the spring clock shift.
In stratified analyses, the elevation tended to be more pronounced in patients having low cholesterol and triglycerides and, to some extent, among those taking cardiac medications such as aspirin or calcium-channel blockers.
In secondary analyses,
Discussion
In a largely overlapping population, we confirmed our previous finding [4] that there is a short term increase in risk for AMI after the transition into DST. The effect size of the association was somewhat smaller than in our previous study. The effect of transition out of DST on the first week was weak and statistically non-significant. However, given the precision of our estimates, our data do not exclude increases and decreases in AMI risk associated with DST transitions of the magnitude we
Limitations
As we discussed above, a limitation of the present study is the delay in CCU admissions. The magnitude of this delay was not recorded, but most likely resulted in a dilution of the observed effects and might have confounded the effects of individual factors on the association between DST shifts and AMI incidence. We hypothesize that the delay could have contributed to the higher incidence ratios among individuals with higher probability for an AMI. However, not all such factors seem likely to
Conclusion
In a sample of AMI patients, we confirmed that, after the transition into DST, there is a modest short-term increase in the incidence of AMI. The most plausible explanation for our findings is the adverse effect of sleep deprivation and circadian misalignment on cardiovascular health. Our data suggest that even modest sleep deprivation and disturbances in the sleep–wake cycle might increase the risk of AMI, and that it may be possible to identify higher-risk subgroups at which to target
Conflicts of interest
The ICMJE Uniform Disclosure Form for Potential Conflict of Interest associated with this article can be viewed by clicking on the following link: doi:10.1016/j.sleep.2011.07.019.
Acknowledgements
We acknowledge the unfortunate and untimely death of Dr. Stenestrand during the preparation of this manuscript. He will be greatly missed. Dr. Janszky was supported by the Swedish Council of Working Life and Social Research, the Karolinska Institute Foundation, and the Ansgarius Foundation.
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Sleep, health, and human capital: Evidence from daylight saving time
2020, Journal of Economic Behavior and OrganizationCitation Excerpt :As mentioned, most existing studies (in economics and outside of economics) have focused on spring DST and provided statistically significant effects. At the same time, the majority of these studies have failed to produce the same statistical effects for fall DST (cf. Lahti et al., 2008; Barnes and Wagner, 2009; Janszky et al., 2012; Jiddou et al., 2013; Harrison 2013a, 2013b). Our study shows the opposite picture, which we consider one contribution to the literature on the health effects of daylight saving time.