Heure d'été : Pourquoi le changement d'heure peut affecter notre santé

Why do our clocks change?

In Britain, the clocks will move back by one hour at 2am on Sunday 26th October. We change the clocks to make better use of natural daylight in the morning.

Between March and October - during Daylight Saving Time - an hour of daylight is borrowed from the morning and added to the end of the day. At the end of October, we push the clocks back and return to standard time or Greenwich Mean Time.

The United States, Canada, Australia and New Zealand - as well as European countries such as France, Germany, Italy, Poland and Spain - also change their clocks.

Every year, the clock change causes a discussion about whether we should continue the practice. Some people welcome the change as it marks the start of a new season, but others argue that it’s an inconvenience.

However, some researchers suggest that changing the clocks can have a serious effect on our health because of the disruption to our circadian rhythms.

According to research, moving our clocks forward or back by an hour can disturb these natural rhythms - leading to several health issues.

Increase in mood disorders

Research has linked the clocks changing to an increase in mood disorders such as dépression ou trouble affectif saisonnier. When the clocks go forward in the spring, it means we have darker mornings and lighter evenings.

Less morning light can lower levels of the mood-boosting hormone serotonin, which can affect how you feel emotionally - especially if you already have a mental health issue such as depression.

Research has also linked the clocks going back to mood disorders. A US study found an 11% increase in depressive episodes during the switch from daylight saving to standard time.

Disrupted sleep

The clocks changing can also affect our sleep schedules, which in turn can affect our mood and ability to concentrate. The shift may mean we go to bed and wake up earlier or later than usual - and the disruption could lead to insomnie or interrupted sleep.

Although these issues are usually temporary - lasting a few days or weeks - it can make us feel tired and foggy.

This fatigue may also lead to accidents. A study of 732,000 car accidents over two decades found that the annual switch to Daylight Saving Time is associated with a 6% increase in fatal car crashes that week.

Increased chance of cardiovascular disease

The disruption to our circadian rhythms may also be linked to heart disease, according to some studies - although the exact reason why is unknown.

A study review found that the chance of heart attacks increased “modestly but significantly” after the shift to daylight saving time in the spring but not in winter clock change.

According to the researchers, the abrupt change to the ‘sleep-wake cycle’ has been linked to inflammation and imbalances in the nervous system.

Another study found that moving into daylight saving time is associated with a higher chance of maladie cardiovasculaire, mental health issues and immune-related disorders.