Summer time: what are its effects on our health?

On the night of Sunday March 27, our phones and other connected devices will jump in time one hour. The time displayed on the screens will automatically change from 2 a.m. to 3 a.m. to accompany the change to summer time. If, for most people, this change of time will have little or no visible consequences, several research works underline however that it can be associated with effects on our biological clock and significant consequences for our health.

Scientific literature shows that the time change does indeed have physiological and health effects: it impacts our internal biological clock (called the circadian system) and can induce harmful effects on our health (sleeping troublesalertness, accidents work and the road, depression, myocardial infarction and cerebrovascular accidents).

The body’s adaptation to this jet lag that we impose on it will vary from one individual to another and can last a few days for chronotypes morning (people who tend to be more efficient in the morning), to several months for late chronotypes (people who tend to be more efficient in the evening). In the context of this time change, small children and the elderly are more likely to experience negative effects, but this is also the case for teenagersfrom night workersand of all those suffering from a sleep and who will have more difficulty adapting to the new schedule.

Disadvantaged night owls

Moreover, according to the opinion of specialists, such as the neurobiologist and Inserm researcher Claude Gronfier, president of the French Society of Chronobiology, the transition to summer time would be more complicated to manage for the organism than the transition to ‘hour of’wintertaking into account on the one hand the loss of one hour of sleep, and on the other hand the fact that thebiological clock should be brought forward one hour.

On average, our bodies tend to lag 10 minutes into their 24-hour cycle. With the time change, they would be asked to advance their rhythm by one hour, which would accentuate the efforts made by our body to try to catch up. This change would be particularly badly experienced by the latest chronotypes, those registering an average of 30 minutes behind their 24-hour cycle. The effects of the change to summer time on our circadian rhythm would be accentuated by the general lack of sleep of the French population, estimated between 30 and 90 minutes per day according to the studies (60 minutes according to barometer 2022 from the National Institute of Sleep and Vigilance).

Why maintain summer time and winter time?

The removal of the seasonal time change having been voted in 2019, member states of the European Union must now choose which definitive time to adopt. The vast majority of the scientific community recommends that the choice be carries on maintaining winter time.

If we were to maintain daylight saving time all year round, waking up in winter and going to bed in summer would indeed be more difficult. 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 standard time or “winter time”), and this very late sunrise in this season winter would have a harmful impact on the health of the French, the setting of our biological clock is also done by exposure to light.

When we wake up, our body needs a large dose of light to start a new day and synchronize the biological clock. It would thus be deprived of this light in winter with later sunrise.

On the other hand, if winter time were maintained, sunset would take place on average 4 hours later in summer than in winter, instead of 3 hours with the current time change, and would induce an earlier sunset and longer sleep which would be beneficial to our health.

Work on the importance of exposure to the light on the circadian cycle are carried out at the Lyon Neuroscience Research Center. The research team observed in particular that certain exposures to light at very specific times have beneficial effects on the physiology of sleep and the non-visual functions of the body such as secretion melatonin (a hormone controlled by the circadian clock and involved in the regulation of sleep), the pupillary reflex, brain activity, temperature and the cardiovascular system, even at very short exposures and very low light levels