Daylight saving time was first implemented during the first world war to take advantage of longer daylight hours and save energy. While this made a difference when we heavily relied on coal power, today the benefits are disputed. In fact, emerging research suggests that moving the clocks twice a year has negative impacts, particularly on our health.
During the first days after the clocks change, many people suffer from symptoms such as irritability, less sleep, daytime fatigue, and decreased immune function. More worryingly, heart attacks, strokes and workplace injuries are higher during the first weeks after a clock change compared with other weeks. There’s also a 6% increase in fatal car crashes the week we “spring forward”.
The reason time changes affect us so much is because of our body’s internal biological “clock”. This clock controls our basic physiological functions, such as when we feel hungry, and when we feel tired. This rhythm is known as our circadian rhythm, and is roughly 24 hours long.
The body can’t do everything at once, so every function in the body has a specific time when it works best. For example, even before we wake up in the morning, our internal clock prepares our body for waking. It shuts down the pineal gland’s production of the sleep hormone melatonin and starts releasing cortisol, a hormone that regulates metabolism.
Our breathing also becomes faster, our blood pressure rises, our heart beats quicker, and our body temperature increases slightly. All of this is governed by our internal biological clock.
Our master clock is located in a part of the brain called the hypothalamus. While all tissues and organs in the body have their own clock (known as a peripheral clocks), the brain’s master clock synchronises the peripheral clocks, making sure all tissues work together in harmony at the right time of the day. But twice a year, this rhythm is disrupted when the time changes, meaning the master clock and all the peripheral clocks become out of sync.
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Since our rhythm is not precisely 24 hours, it resets daily using rhythmic cues from the environment. The most consistent environmental cue is light. Light naturally controls these circadian rhythms, and every morning our master clock is fine-tuned to the outside world.
The master clock then tells the peripheral clocks in organs and tissues the time via hormone secretion and nerve cell activity. When we artificially and abruptly change our daily rhythms, the master clock shifts faster than the peripheral clocks and this is why we feel unwell. Our peripheral clocks are still working on the old time and we are experiencing jetlag.
It may take several days or weeks for our body to adjust to the time change and for our tissues and organs to work in harmony again. And, depending on whether you are a natural morning person or a night owl, the spring and autumn clock change might affect you differently.
Night owls tend to find it more difficult to adjust to the spring clock change, whereas morning larks tend to be more affected by the autumn clock change. Some people are even entirely unable to adjust to the time change.
While any disruption to our circadian rhythm can affect our wellbeing, there are still things we can do to help our body better adjust to the new time:
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Keep your sleeping pattern regular before and after the clocks change. It’s particularly important to keep the time you wake up in the morning regular. This is because the body releases cortisol in the morning to make you more alert. Throughout the day you will become increasingly tired as cortisol levels decrease and this will limit the time change’s impact on your sleep.
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Gradually transition your body to the new time by changing your sleep schedule slowly over a week or so. Changing your bedtime 10-15 min earlier or later each day helps your body to gently adjust to the new schedule and eases the jetlag.
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Get some morning sunlight. Morning light helps your body adjust quicker and synchronises your body clock faster – whereas evening light delays your clock. Morning light will also increase your mood and alertness during the day and helps you sleep better at night.
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Avoid bright light in the evening. This includes blue light from mobile phones, tablets, and other electronics. Blue light can delay the release of the sleep hormone melatonin, and reset the internal clock to an even later schedule. A dark environment is best at bedtime.
5) Keep your eating pattern regular. Other environmental cues, such as food, can also synchronise your body clock. Research shows light exposure and food at the correct time, can help your master and peripheral clocks shift at the same speed. Keep mealtimes consistent and avoid late-night meals.
Following a Europe-wide consultation, in March 2019 the European Parliament voted in favour of removing daylight saving time – so this might be one of the last times many European readers have to worry about adjusting their internal clocks after a time change. While member states will decide whether to adopt standard time (from autumn to spring) or daylight saving time (from spring to autumn) permanently, scientists are in favour of keeping to standard time, as this is when the sun’s light most closely matches when we go to work, school, and socialise.
Gisela Helfer receives funding from the Academy of Medical Sciences, the Wellcome Trust, the Government of Business, Energy and Industrial Strategy and the British Heart Foundation and Diabetes UK.