Circadian rhythm

Biological clock and biorhythm. These are terms we often hear with regard to daylight savings time. But what do they actually mean? “Your body’s internal biological clock is called the circadian rhythm, which literally means ‘about a day’, because it follows a cycle of about 24 hours without any time cues,” Smolders explains. “People who spent time in caves, where they had no external time cues such as daylight, followed natural rhythms that usually turned out to be slightly longer than 24 hours. This was discovered because after the study these people thought they had spent fewer days in the caves than was actually the case.”

Our biological clock regulates all kinds of processes in our body, such as our sleep-wake cycle, body temperature, hormone production, and even digestion. “In other words, our body is programmed to carry out specific processes at certain times and to react adaptively to the environment,” says Smolders. For example, it’s set up to be active during the day and sleep at night.

Mini jet lag

When you work at night or travel to a different time zone, your natural rhythm doesn’t correspond with your environment and can become disrupted. Anyone who has ever worked shifts or experienced jet lag knows that disrupting your biorhythm can have a significant impact on your energy, mood, and performance.

But what happens to our rhythm when we move the clocks forward an hour for daylight savings time? Even though this is only a one-hour shift, many people still experience it as a kind of mini jet lag. “Our daily rhythm can be temporarily disrupted and we can experience symptoms such as fatigue or concentration problems,” says Smolders.

Sensitivity to light

Many disruptions to our biorhythm have to do with our sensitivity to time cues, of which light (especially day light) is the most important. “Light plays a crucial role in controlling our biological clock and regulating our sleep-wake cycle,” Smolders explains. “Not only does it influence our sleep-wake cycle, it also affects the quality of our sleep.”

This sensitivity to light also plays a role in the transition to daylight savings time, when it gets light an hour later in the morning and stays light an hour longer in the evening. Ultimately, it’s a combination of different factors – such as working hours, the amount of activity during the day, and personal preferences – that determine how strongly daylight savings time affects our biorhythm.

The shift in the timing of our meals and sleep-wake cycle can also disrupt our biological clock, Smolders explains. As a result, some people may experience fatigue or have trouble falling asleep. “By moving the clock forward an hour, we also miss out on an hour of sleep, which can intensify complaints such as fatigue,” Smolders explains.

Sufficient daylight

Fortunately, our brain is highly adaptive, which means that we can adjust to the new rhythm. “The fact that the circadian rhythm doesn’t exactly correspond to a 24-hour day cycle in most people says a lot about our adaptability,” Smolders explains. It shows that our body is able to adapt to changes, such as the transition to daylight savings time or other disruptions in our day-night rhythm. Although it can sometimes take some time, our body has the capacity to gradually bring itself back into balance, ultimately making us feel better again.

How quickly this happens varies per person. “It can vary from a day to a few weeks,” the researcher says. Exposure to daylight at the right times plays a crucial role in this. “Light in the morning helps to speed up your biological clock, while light in the evening makes this internal clock tick a little slower,” she explains. For example, light in the morning ensures that our body knows when it’s time to get up, while the absence of light in the evening helps us fall asleep.

By exposing ourselves to sufficient daylight at the right times, we can adapt more quickly to daylight savings time and limit its negative effects as much as possible. “It’s a good idea to open the curtains first thing in the morning and spend enough time outside during the day,” recommends Smolders.

Standard time or daylight savings time?

In recent years, there has been increasing criticism of the standard and daylight savings time arrangements. “Although most people can adapt to the new rhythm fairly quickly, it would be better for us to be on standard time all year round,” Smolders argues. But, she emphasizes, that’s purely from a scientific perspective, given our biological clock. There are all kinds of other interests at play, such as energy savings, which is said to have a positive impact on the economy. This was also the main reason for the Netherlands to introduce daylight savings time in 1977.

“The time they keep in the United Kingdom would actually be even better than Dutch standard time,” says Smolders. The United Kingdom uses Greenwich Mean Time, which means that it’s an hour earlier there. "In the UK, the sun is at its highest point at around 12:00 noon, which is more in line with our biological clock," she explains. In the Netherlands, this only happens around 12:40 in the winter and even later – around 13:40 – in the summer, which means we’re actually ‘behind’ the natural solar time. “This means that it stays dark longer in the morning, especially in the winter, while morning light is essential for us to feel energetic and alert.”

The debate about whether or not to keep daylight savings time will continue for a while, but the fact of the matter is that we’ll have to put the clock forward an hour this coming weekend. If that means we’ll suffer from energy dips or concentration problems next week, a refreshing walk across campus – especially in nice weather – would be a good idea. “Both sufficient daylight and physical activity can boost your mood, concentration, and energy level,” Smolders concludes.