On March 29, clocks will move forward by one hour. Most people will lose an hour of sleep, and in the following days, evenings will gradually become longer.

The shift to daylight saving and standard time occurs twice a year. Although there have been multiple attempts to cancel it, every spring the clocks still “jump” forward by one hour.

Seasonal clock changes were first introduced during World War I as a measure to save energy and were reintroduced in many countries in the 1970s. However, today researchers warn about their impact on health, especially the springtime clock change.

Changing the clock by just one hour may seem trivial, but studies show—and experts note—that the consequences are more serious than many realize. Even a one-hour shift can disrupt our circadian rhythm—the internal 24-hour clock that regulates sleep, wakefulness, hormone production, and mood.

“Most people are able to adjust within a week, but we know there are those for whom it is much harder: their internal clocks may take weeks, or even months, to adapt even to a one-hour difference,” told Euronews Health Jeffrey C. Kelso, a postdoctoral researcher studying circadian rhythms at the Royal College of London.

According to him, genetics largely determine the functioning of internal clocks, and further research is needed to understand why some people adapt more slowly than others.

In addition to sleep disruptions, the springtime clock change has been linked to a temporary increase in traffic accidents, heart attacks, and depressive episodes. Many people welcome the springtime change: the days are longer, and the sun sets later.

However, Kelso warns that if a person stays exposed to light late into the evening, the body finds it harder to recognize that it’s time to relax and prepare for sleep. “Light suppresses melatonin production, which shifts the timing of sleep and can make it harder for people to fall asleep,” Kelso notes.

Melatonin is a hormone secreted by the pineal gland when the body starts preparing for sleep. Its production peaks in darkness, while exposure to light lowers its levels.

Kelso emphasizes that drawing curtains before bedtime and completely blocking external light is beneficial for sleep quality: it signals to the body that the day has ended.

When circadian rhythms are stable, internal clocks are well-synchronized with the 24-hour cycle and provide clear signals for the proper functioning of the body’s core processes.

People with strong circadian rhythms generally maintain a stable sleep-wake schedule, even if routines or seasons change.

Disruptions to biological clocks—caused by irregular sleep and eating patterns, crossing time zones, shift work, or bright light at night—have been linked to numerous health issues, including a higher risk of obesity, cardiovascular disease, type 2 diabetes, and hypertension.