One hour less sleep. But one more hour of sunshine. Like every last Sunday in March, we will switch to summer time. So this weekend, during the night from Saturday to Sunday, at 2 o’clock, it will be 3 o’clock.
For many, this officially launches spring, and finally portends long sunny and friendly evenings (finally, when the sun decides to show itself again). But if the change to summer time is synonymous with well-being for many of us, is it really good for our health?
“Deleterious effects” on our internal clock
In the opinion of specialists, “the switch to summer time would be more complicated for the body to manage than the switch to winter time, taking into account, on the one hand, the loss of an hour of sleep, and on the other, the fact that the biological clock will have to be advanced by one hour”, estimates the neurobiologist and Inserm researcher Claude Gronfier, president of the French Society of Chronobiology. A shift which causes “physiological and health effects: it impacts our internal biological clock, called the circadian system, and can induce harmful effects on our health, such as sleep disorders, vigilance, work and road accidents, depression, myocardial infarction and stroke,” warns Inserm.
Moreover, “several studies demonstrate this: during the transition to summer time, which induces the loss of an hour of sleep, people who have a late chronotype, that is to say people who go to bed -late and late risers, are more likely to develop health problems in the days following the time change. This ranges from road, work or domestic accidents – linked to a state of drowsiness – to cardiovascular problems,” explains Dr Maxime Elbaz, doctor in neuroscience, sleep specialist and scientific director at BioSerenity. And if strokes and myocardial infarctions increase each year when summer time changes, “this is due to a clash of rhythms,” continues Dr. Elbaz. The rhythm of the heart rate follows the circadian rhythm, and if the second is altered, the first risks also being altered by ricochet, it is physiological.”
A clash of rhythms which also explains why “it is especially the elderly and babies who are most affected by this time change”. Accustomed to fixed meal and sleep times, this one-hour gap is more difficult for these age groups to overcome.
Resynchronize your internal clock
As the transition to summer time disrupts our internal clock, it is important to resynchronize it. “It is advisable, the day before and two days before the time change, to bring your bedtime forward by thirty minutes each evening,” says Dr. Elbaz, “in order to make this time change as painless as possible.” possible for the organism. But in practice, these scientific recommendations are not followed by the majority of people. And many people attack Monday morning with a painful feeling of jet lag. Happy coincidence of the calendar, with Easter falling this weekend, this Monday will be a holiday and will give us one more day to recover.
However, if you had to follow at least one piece of advice to avoid having your head fogged by the time change, “it is to take light baths, as much as possible when you wake up in the morning,” recommends the sleep specialist. This effectively resynchronizes our circadian rhythm, setting our internal clock back on time.”
How ? “By waking up an hour earlier than our usual schedule, we will be sleep deprived, and have a still high melatonin level, characterized by this state of inertia and drowsiness,” explains Dr. Elbaz. In the same way, our cortisol level, which is the wake-up and stress hormone, will also be disrupted and shifted, because its production is delayed by the time change. However, exposing yourself to natural light promotes the secretion of cortisol, which allows you to feel in good shape.” This is also why people who go to bed early and rise early, who, by their chronotype, are better aligned with the sun, suffer less on this weekend when you have to set your watch forward an hour.
Another piece of advice, also valid every other day of the year but not to be forgotten when summer time changes: “do not scroll on your smartphone at bedtime, its light disrupts the secretion of melatonin, therefore falling asleep,” insists the sleep specialist. Finally, adaptation to the time change “varies from one person to another,” reassures Dr. Elbaz. For some, it may take time, for the majority, everything will be back to normal within the next two to three days.”
The removal of the time change under debate
So, in 2024, is changing time still consistent? Established in France by a decree in 1975 following the oil crisis of 1973-1974, the switch to summer time was intended to save energy: the additional hour of sunlight at the end of the day was to make it possible to reduce the time – therefore the costs – lighting in the evening. But according to Ademein recent years, the annual savings made are of the order of 351 GWh, or barely 0.07% of total electricity consumption.
Enough to fuel the debate on the definitive abolition of the time change. A deletion was also made in March 2019, when the European Parliament voted for a draft directive removing the seasonal time change, supposed to be effective from 2021. But the Covid-19 crisis postponed the text indefinitely. If it were put back on the table, EU member states would have to “choose which definitive time to adopt” between winter time and summer time, recalls Inserm, which emphasizes that “the vast majority of the scientific community recommends that the choice be made to maintain winter time.”
A debate “where chronobiological considerations and political-economic interests conflict,” summarizes Dr. Elbaz. What we know is that winter time is the most physiological, the most in phase with our internal clock.” Fixed at GMT+1, winter time is already one hour later than solar time on the Greenwich meridian. Summer time is therefore two behind the sun. “If we were to maintain summer time all year round, waking up in winter and going to bed in summer would in fact be more difficult,” warns Inserm. On the shortest day of the year, December 21, the sun would rise in Paris at 9:41 a.m., instead of 8:41 a.m. in winter time, which would have a harmful impact on the health of the French, the setting of our biological clock is also activated by exposure to light.”
The scientific argument, however, struggles to convince public opinion: during a French consultation launched by the European Affairs Commission in 2019, if more than 80% of respondents were in favor of definitively removing the change in At this time, nearly 60% of respondents favored the definitive adoption of summer time.