Neuroscience and psychology
Scientific evidence of time change: effects on health, chronodisruption, and energy savings
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Ainhoa Pérez
Alumni
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MPH, MSc.
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Time changes are used by different countries around the world. However, in recent decades, various regions have been abandoning the switch to daylight saving time, as evidence of energy savings is not as clear as previously assumed, and there are potential health consequences. However, the debate over daylight saving time is more complex than it is sometimes presented.
Neither option provides natural, progressive circadian synchronization with the light that varies naturally throughout the year. In addition, some regions within the same time zone may not be well synchronized with sunrise and the natural light cycle at the start of the day and may need different schedules (e.g., northwest vs. southeast). Some research shows that, for example, there may be a substantially higher number of traffic accidents in these regions with schedules less aligned with the general time zone (Gentry et al 2022), so this fact may not be anecdotal. In some areas of Spain, the social clock may be more than two hours ahead of the actual position of the sun, which marks the natural schedule of light and dark cycles.
Outside clock societies, the rooster would crow a little earlier each day starting in winter, and social rhythms would gradually adapt to the cycles of light, with progressively longer days in spring, etc. But the time marked by our clocks continues to follow its mechanical rhythm without adapting to geophysical rhythms.
Various meta-analyses of studies have shown that there is an increased risk of acute myocardial infarction during the first week after time changes, particularly during the spring time change. For this reason, many authors have suggested that daylight saving time should be eliminated (Manfredini et al 2019). In addition, the latest systematic review published is consistent with the findings, showing a consistent increase in the number of heart attacks (Hurst et al, 2024). People over the age of 65 seem to be more susceptible to an increased risk of heart attack after time changes, and the increased risk seems to occur only during the switch to daylight saving time in the spring.
Another interesting question is whether we sleep better in summer or winter. Although it has been suggested that the earlier arrival of night in winter causes people to go to bed earlier, it is not clear that this actually increases sleep time. Some studies suggest that people take longer to fall asleep and wake up later. Exposure to daylight may in fact be a better predictor of sleep than the time at which it gets dark (Dunster et al, 2022), so the regulatory effects of light on sleep-wake cycles may be more important during the day than at night. This suggests that in places where exposure to sunlight is limited during the winter, melatonin production may be altered, affecting both the quality and quantity of sleep. However, rest also depends on temperature, and some people sleep less and worse in hot months.
Nevertheless, with the creation of artificial light, synchrony occurs to a greater extent with social rhythms, i.e., the social clock. Additionally, the impact on health depends on individual chronotypes, with some people being more morning people and others being more evening people. The morning chronotype is associated with better physical and psychological health. Even in people with a natural evening chronotype who switch to a more morning-oriented lifestyle.
Due to the rotation of the Earth, our cells have adapted to these cycles of light and darkness in sync with the Earth's rotation for millions of years, regulating their biological activity and optimizing hormone production through the activation of environmental signals that mark the rhythms of activity and sleep. As human beings, our evolution has followed the same pattern, as we spent our days outdoors and our nights sheltered. Our bodies are subject to the interaction of three clocks:
· Biological clock: our internal cellular rhythms, adapted over millions of years to cycles of light and darkness.
· Solar clock: the geophysical solar time of the region, with noon being when the sun is highest.
· Social clock: the time set by our watches and social obligations.
Time changes affect the synchronisation between these clocks. However, the use of artificial lighting has reduced the sun's role as an essential synchroniser of our biological rhythms. Therefore, in terms of health risks, the debate on time changes is simplistic if it only considers the effect on the solar clock. The time change is mainly annoying, and no decision about our schedules is well suited to geophysical and circadian rhythms throughout the year. However, evidence shows that the establishment of daylight saving time is questionable.
And remember: the two great symbols of industrial society are the clock and coffee.
WHY ARE TIMES CHANGED?
Sunlight has marked the beginning of human activity in different societies throughout history. However, with the invention of the clock (in the modern sense, a wind-up device), human activity shifted to a fixed mechanical schedule marked by these devices, which do not reflect the variation in light and dark cycles throughout the year. Due to the tilt of the Earth's axis, the time at which dawn breaks and the length of the days change with the seasons, while clocks follow a fixed time pattern. For example, in Spain, the time at which dawn breaks changes by about 3 hours between spring and winter. This makes it reasonable to vary the time on our clocks throughout the year, changing the time with the seasons. The other option would be to stick with a fixed time zone throughout the year. In this case, we would have to decide which one, and we would have the problem that the clock's rhythm would not adapt to sunrise in some months.Neither option provides natural, progressive circadian synchronization with the light that varies naturally throughout the year. In addition, some regions within the same time zone may not be well synchronized with sunrise and the natural light cycle at the start of the day and may need different schedules (e.g., northwest vs. southeast). Some research shows that, for example, there may be a substantially higher number of traffic accidents in these regions with schedules less aligned with the general time zone (Gentry et al 2022), so this fact may not be anecdotal. In some areas of Spain, the social clock may be more than two hours ahead of the actual position of the sun, which marks the natural schedule of light and dark cycles.
Outside clock societies, the rooster would crow a little earlier each day starting in winter, and social rhythms would gradually adapt to the cycles of light, with progressively longer days in spring, etc. But the time marked by our clocks continues to follow its mechanical rhythm without adapting to geophysical rhythms.
DOES IT SAVE ENERGY?
The main reason given for the time change is the energy savings in the region that applies daylight saving time. Since it gets light earlier, moving the clocks forward aligns work and industrial activity with the morning light, assuming that this means less electricity is consumed at night. However, the evidence is not entirely clear, and studies as a whole show that the energy savings are too small to justify the time change on their own. For example, the most comprehensive meta-analysis on this issue (Havranek et al, 2018), compiling 44 studies, including government and energy company reports, shows that the average saving is around 0.3% of total electricity consumption on the days when it is applied. Countries closer to the equator tend to increase their consumption, while countries further from the equator show greater savings, so it should be noted that the effect may vary depending on the country, latitude, and other factors. However, energy consumption is not the only criterion to be taken into account when deciding on a country's time schedule.IMPACT OF DAYLIGHT SAVING TIME ON HEALTH
One of the most immediate effects of the switch to daylight saving time is that it causes a reduction in sleep, leading to drowsiness during the day. However, the problem with daylight saving time is not that we sleep one hour less on one day a year. Most people easily recover a one-hour sleep deficit in a single day. However, with the time change, many people report problems for weeks. This is due to chronodisruption, i.e., the desynchronization between the biological clock that the person's body keeps active through physiological inertia and the new time set by the clock. We wake up with cortisol, accumulate adenosine during the day, and sleep with melatonin. When these rhythms are disrupted, behavioral and health problems can arise. Some studies have documented that after the time change there is an increase in medical emergencies in general, a higher number of heart attacks, a higher number of strokes, traffic accidents, etc.Various meta-analyses of studies have shown that there is an increased risk of acute myocardial infarction during the first week after time changes, particularly during the spring time change. For this reason, many authors have suggested that daylight saving time should be eliminated (Manfredini et al 2019). In addition, the latest systematic review published is consistent with the findings, showing a consistent increase in the number of heart attacks (Hurst et al, 2024). People over the age of 65 seem to be more susceptible to an increased risk of heart attack after time changes, and the increased risk seems to occur only during the switch to daylight saving time in the spring.
Another interesting question is whether we sleep better in summer or winter. Although it has been suggested that the earlier arrival of night in winter causes people to go to bed earlier, it is not clear that this actually increases sleep time. Some studies suggest that people take longer to fall asleep and wake up later. Exposure to daylight may in fact be a better predictor of sleep than the time at which it gets dark (Dunster et al, 2022), so the regulatory effects of light on sleep-wake cycles may be more important during the day than at night. This suggests that in places where exposure to sunlight is limited during the winter, melatonin production may be altered, affecting both the quality and quantity of sleep. However, rest also depends on temperature, and some people sleep less and worse in hot months.
Nevertheless, with the creation of artificial light, synchrony occurs to a greater extent with social rhythms, i.e., the social clock. Additionally, the impact on health depends on individual chronotypes, with some people being more morning people and others being more evening people. The morning chronotype is associated with better physical and psychological health. Even in people with a natural evening chronotype who switch to a more morning-oriented lifestyle.
CONCLUSION
The clock sets the pace for modern industrial society. In 1884, the International Meridian Conference was held to divide the earth into 24 time zones. Time changes, specifically daylight saving time, were implemented in Europe during World War I as a measure to reduce the consumption of coal and electricity, which were critical resources for the war effort. Since then, countries have been experimenting with different schedules, with far more uncertainty than is sometimes implied.Due to the rotation of the Earth, our cells have adapted to these cycles of light and darkness in sync with the Earth's rotation for millions of years, regulating their biological activity and optimizing hormone production through the activation of environmental signals that mark the rhythms of activity and sleep. As human beings, our evolution has followed the same pattern, as we spent our days outdoors and our nights sheltered. Our bodies are subject to the interaction of three clocks:
· Biological clock: our internal cellular rhythms, adapted over millions of years to cycles of light and darkness.
· Solar clock: the geophysical solar time of the region, with noon being when the sun is highest.
· Social clock: the time set by our watches and social obligations.
Time changes affect the synchronisation between these clocks. However, the use of artificial lighting has reduced the sun's role as an essential synchroniser of our biological rhythms. Therefore, in terms of health risks, the debate on time changes is simplistic if it only considers the effect on the solar clock. The time change is mainly annoying, and no decision about our schedules is well suited to geophysical and circadian rhythms throughout the year. However, evidence shows that the establishment of daylight saving time is questionable.
And remember: the two great symbols of industrial society are the clock and coffee.
#Chronodisruption #chronobiology #timechange
References:
Dunster, G. P., Hua, I., Grahe, A., Fleischer, J. G., Panda, S., Wright, K. P. Jr., Vetter, C., Doherty, J. H., & de la Iglesia, H. O. (2022). Daytime light exposure is a strong predictor of seasonal variation in sleep and circadian timing of university students. Journal of Pineal Research, 74(1), e12843. https://doi.org/10.1111/jpi.12843
Gentry, J., Evaniuck, J., & Mali, I. (2022). Living in the wrong time zone: Elevated risk of traffic fatalities in eccentric time localities. Time & Society, 31(4). https://doi.org/10.1177/0961463X221104675
Havranek, T., Herman, D., & Irsova, Z. (2018). Does daylight saving save electricity? A meta-analysis. The Energy Journal, 39(2), 35-61. https://doi.org/10.5547/01956574.39.2.thav
Hurst, A., Morfeld, P., Lewis, P., & Erren, T. C. (2024). Daylight saving time transitions and risk of heart attack: A systematic review and meta-analysis. Dtsch Arztebl Int, 121, 490-496. https://doi.org/10.3238/arztebl.m2024.0078
Manfredini, R., Fabbian, F., Cappadona, R., De Giorgi, A., Bravi, F., Carradori, T., Flacco, M. E., & Manzoli, L. (2019). Daylight saving time and acute myocardial infarction: A meta-analysis. Journal of Clinical Medicine, 8(3), 404. https://doi.org/10.3390/jcm8030404
Roenneberg, T., Winnebeck, E. C., & Klerman, E. B. (2019). Daylight Saving Time and Artificial Time Zones - A Battle Between Biological and Social Times. Frontiers in physiology, 10, 944. https://doi.org/10.3389/fphys.2019.00944
* The news published on studies do not represent an official position of ICNS, nor a clinical recommendation.
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