Do you find the changeover to summertime more difficult than to wintertime every year? Does this time change make sense at all?
Dr. Beth Malow is a neurologist and head of the Department of Sleep Disorders at Vanderbilt University, Nashville, Tennessee. In a recent article in the Journal of the American Medical Association, she explains what time change does to the body and what studies say about it.1
The European Parliament has already voted to abolish the time change in 2021. In the future, individual EU states could decide for themselves whether they want winter or summer time permanently. The change is still uncertain, however, because the EU countries would have to agree to it by a majority, which does not seem to be in sight at the moment. According to diplomatic circles in Brussels, the majority of states still have no position. There is concern that the effects of a change have not been sufficiently investigated.2
The effects of permanent summertime have indeed not been widely researched to date, but Dr. Marlow has illustrated how the change to summer time can have adverse health effects, including cardiovascular and cerebrovascular ones, by using current studies.
For example, the rate of apoplexy is increased in the first two days after the switch to summertime, with the elderly, cancer patients and women appearing to be particularly vulnerable.3 Data from over 100.000 people also show a 5% increase in myocardial infarctions in the first week after the time change.4
Further research has shown that people sleep shorter and suffer poorer sleep quality each night as a result of the change. Dr. Malow believes that the above-mentioned problems could be the effects of partial sleep deprivation, changes in sympathetic nervous system activity (due to increased heart rate and blood pressure), and the release of proinflammatory cytokines.
The subjective well-being, recorded in standardized analyses, also suffered from the changeover to summertime, most markedly among full-time employees and men.
A small study also found longer reaction times, increased vigilance gaps and increased daytime tiredness among students. The study was limited to the week following the time change, but the effect of chronic sleep deprivation on attention, behavior, learning difficulties, depression and self-harm is described in detailed reviews, which also form the basis for the recommendations of the American Academy of Sleep Medicine (including regular 8-10 sleep hours for adolescents).
Dr. Malow believes that further studies are needed to analyze whether the change to summer time has other long-term associations with sleep in adolescents and contributes to adverse health effects.
The circadian clock is a self-regulating feedback loop encoded by genetic factors. The adverse health effects of the summertime change may be related to disturbances in the underlying genetic mechanisms involved in the expression of the circadian clock. Shifting bedtime results in a global disruption of peripheral gene expression and even the short-term sleep deprivation that occurs during the changeover could alter epigenetic and transcriptional profiles of the genes involved in the circadian clock.5,6
While it is still unclear how serious a time change of one hour is for otherwise healthy people, Dr. Malow believes it is quite possible that people with extreme forms of chronotypes, or people with circadian rhythm disorders, as well as individuals with neurological disorders, or children and adolescents whose brains are still developing, could be more susceptible to the negative side effects of the changeover to summertime.
References:
1. Malow, B. A., Veatch, O. J. & Bagai, K. Are Daylight Saving Time Changes Bad for the Brain? JAMA Neurol (2019) doi:10.1001/jamaneurol.2019.3780.
2. (In German only) Letzte Zeitumstellung noch nicht 2019 - so geht es jetzt weiter. https://www.merkur.de https://www.merkur.de/politik/letzte-zeitumstellung-noch-nicht-2019-so-geht-es-jetzt-weiter-zr-10198082.html (2019).
3. Sipilä, J. O. T., Ruuskanen, J. O., Rautava, P. & Kytö, V. Changes in ischemic stroke occurrence following daylight saving time transitions. Sleep Med. 27–28, 20–24 (2016).
4. Manfredini, R. et al. Daylight Saving Time and Acute Myocardial Infarction: A Meta-Analysis. J Clin Med 8, (2019).
5. Cedernaes, J. et al. Acute sleep loss results in tissue-specific alterations in genome-wide DNA methylation state and metabolic fuel utilization in humans. Sci Adv 4, eaar8590 (2018).
6. Cedernaes, J. et al. Acute Sleep Loss Induces Tissue-Specific Epigenetic and Transcriptional Alterations to Circadian Clock Genes in Men. J. Clin. Endocrinol. Metab. 100, E1255-1261 (2015).