As the last weekend in March and its October counterpart approaches, a historic debate over thedesirability of abandoning or maintaining the practice of move the clock forward or backward. In this discussion of seasonal time shift These are influenced, among others, by economic, energetic, physical, safety and public health considerations. Regarding this last question, the conclusions of some studies present alarming data. “Sometimes we see scary headlines about the time change. I even read things like that the risk of heart attack among women increases by 25% because of this. However, we are facing statistical fraud, biased data due to low sample size of the study”, says Jorge Mira Pérez, professor of Electromagnetism at the Department of Applied Physics at the University of Santiago de Compostela.

This physicist and his colleague José María Martín Olalla, professor at the Faculty of Physics at the University of Seville, have just published a study that delimits the health risks which part of the scientific literature attributes to the seasonal change of weather. In it, they analyze the 13 most cited articles in this field, used in evaluation reports of the European Commission to question the viability of the practice of time change. And they conclude that the results of these statistical analyzes are based on insufficient analytical samples, that is, with reduced numbers of cases, which increases the margin of error in the final result. “If in an area you see an average of 4 heart attacks a day, that doesn’t mean there are 4 heart attacks every day. Today you might have 3, tomorrow 5, etc. If the next day the time changes, you’ll see 6 infarctions, it cannot be said that the risk of infarction due to the time change increases by 50%; in fact, if the analysis were carried out in an area with an average of 400 infarctions per day, it would be observed that the percentage variations are much smaller”, explains Mira.

Specifically, the article entitled Sample size bias in the empirical assessment of acute risks associated with daylight saving time transitions, published in the international journal Chronobiology, addresses the methodology used in eight articles that measure the influence of time change on myocardial infarctions and ischemia; and five other articles that do so based on data from traffic accidents and admissions to the emergency room due to trauma. The Spanish investigators analyze the relationship between the estimated risk and the total number of investigated cases and limit the incidence of risks associated with the spring shift to 5%, while for the autumn shift they do not detect associated increases. “The works that call the most attention are those that report the greatest risks; we observe that they are also those that are limited to a more specific region or a shorter period of years; discounting the size of the study, all the results are compatible with a 5% risk increase, which is usually classified as mild”, explains Martín Olalla. And he adds: “According to our conclusions, scientific studies that question the viability of the seasonal change of weather attributing harmful effects to human health may be generating a unnecessary alarm“.

Just a few weeks ago, the same researchers challenged a manifesto by the Society for Sleep Research that called for eliminating daylight saving time in the United States and keeping winter time. “At our latitude we will continue to rise early in summer and late in winter; the time change is a way of linking the beginning of the workday with sunrise”, says Mira. José María Martín Olalla, professor at the Faculty of Physics at the University of Seville, is of the same opinion: “In 1811, the Courts of Cádiz had a session schedule in winter and another in summer. summer, we now have a summer schedule and a winter schedule that we do exactly the same with. This seasonal shift in time helps to delay activity in the winter and start with natural light, and move forward in the summer so that the core hours of the day are avoided and more daytime leisure is available after the working day”.

a matter of physics

For them, time change is required. “Early humans rose with the sun, but those of us today rise with a clock, which goes into a fixed gear without regard for the sun. of the sun,” he says. . And they argue: “In Spain, we have 15 and a half hours of daylight in summer and 9 hours in winter. Variation is important. Sunrise and sunset times change by about 3 hours every 6 months. months (around the summer solstice) the sun beats brighter in Madrid than in central Kenya and for three months around the winter solstice there is less sun than on most of the coast of Antarctica. rotation in relation to that which marks the translation around the Sun. It is 23.5°. That’s why we change the time twice a year: because these tilt variations cause the day’s trigger point to fluctuate too much.”

Jorge Mira is one of the partners that has participated in the Commission of experts to study the reform of the official timetable established by the Government of Spain to assess the costs of time changes, particularly those that affect energy efficiency and the economic impact of different productive activities, as well as the benefits, especially the possible positive impacts on people’s health . In the resulting study, published in 2019, the experts proposed maintaining the seasonal change of weather, as is currently done. Experts argued that “after maintaining the current one for 80 years, the Spanish population has developed an adaptation to that schedule and there are not enough reasons to change it”.

Study of the risks associated with the non-practice of said change in schedule

For both Mira and Martín Olalla, the risk assessment process associated with the time change must also include a study of the risks associated with the non-practice of said time change. “There are countries that have practiced the seasonal change of weather for over 100 years without incident, now statistical techniques and the rigor of records allow us to refine calculations and identify social and health impacts, which previously went unnoticed because they were small compared to the multiple factors that influence the problem”, says Jorge Mira. And, based on their studies, they propose a reconsideration of the date of the time change that occurs in autumn. “With the current model, the autumn shift is long overdue and causes a significant part of the October work to start at night, which is an unnecessary risk on those dates,” says Martín Olalla.

three points of view

Expert opinion on the seasonal time change has never been unanimous or conclusive. While there are those who say it is “necessary”, another important fraction chooses to adopt winter time throughout the year -its correct name is “standard time”- mainly in view of health criteria and taking advantage of the hours of sunlight. Physiologists defend its advantages by arguing that it is more in line with the light and dark cycles, that is, we receive more light during school and work hours, which benefits concentration, and there is more darkness at night, which helps us to fall sleep. There are also specialists in favor of maintaining summer time or summer time (DST), taking into account a predictable negative impact on the tourism sector, which represents around 12% of our GDP. This last option is the most valued by the population. According to barometer data from April 2022 from the Center for Sociological Research (CIS), 65% of Spaniards prefer to put an end to seasonal time changes and, of these, 70.9% choose to define daylight saving time.

Economic analyzes were carried out on the impacts of this measure on the tourism and trade sectors; road safety studies on the difficulties that drivers may have in traveling at night; and research in chronobiology, the science that studies the biological and circadian rhythms of the human body and how they can be affected by changes in light and dark patterns.

O Spanish Sleep Society It has been one of the entities that has given special emphasis to the risks of changing weather. He advises keeping a stable schedule without changes throughout the year and betting on winter. “Thanks to this, greater exposure to the sun would be achieved during the most common hours of work and school (8:00 am to 5:00 pm), mainly in the early hours of the morning”, they point out. According to experts in chronobiology, seasonal changes “alter circadian rhythms and some people may have difficulty falling asleep and waking up, especially children and the elderly, especially if they take anxiolytics or antidepressants that affect brain function, the biological sleep-wake cycle and the structure from a psychological point of view, according to some specialists, the standard schedule can worsen mental health, especially in people who already had depressive symptoms. tiredness, lassitude, drowsiness or lack of concentration, among others. Which leads to worse performance”.