Why the clocks changing twice a year is bad for your health

Are you sleeping better since the clocks changed last week? According to science, you should be. And you may notice your productivity improves as your body settles into its winter circadian rhythm.
We have just reverted to permanent standard time, having spent the spring and summer months in daylight savings time (DST). This savings time was first implemented during the first World War. During the second World War, Britain even introduced double savings time (a two-hour clock change). The proposal was that having extra light later into the afternoon would save energy by decreasing the need for electric lighting. This idea has since been found to be inaccurate, as heating needs may increase. Clock changes pose a challenge to our circadian health.
Our master biological 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 peripheral clocks), the brain’s master clock synchronises the peripheral clocks, making sure our organs work together in harmony. But, twice a year, this rhythm is disrupted when the time changes, meaning the master clock and all the peripheral clocks move out of sync – the master clock shifting faster than the peripheral clocks.
Our biological clocks follow a circadian rhythm, around (circa) which the day (dies) revolves. The circadian rhythm is an internal clock that makes the brain cycle between intervals of alertness and sleepiness. Circadian rhythms comprise various elements that influence these intervals, including eating habits, body temperature and duration of sleep, as well as external factors such as darkness and lightness.
In terms of our health, the evidence suggests that moving to DST in the spring is detrimental. Scientists in the US and Scandinavia used the electronic health records of hundreds of millions of people across the US and Sweden to measure the health effects associated with the shift to DST. In a 2020 report in the journal PLoS Computational Biology, they confirmed a significant increase in fatal traffic accidents (up to 30 per cent on the day of commencing DST), a short-term rise in workplace injuries (5.7 per cent after the spring DST shift as employees sleep 40 minutes less on average) and elevated rates of acute heart attacks (up by about 4 per cent).
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In a recently released consensus position statement on clock changes, the British Sleep Society (BSS) said we “should abolish the twice-yearly clock change to prevent the acute adverse effects on sleep, health, performance and safety”.
The statement, which has the support of the Irish Sleep Society, goes on to strongly recommend the restoration of permanent standard time. “This option is preferable to twice-yearly changes to DST, and strongly preferable to permanent DST,” it says.
Why is moving the clocks forward worse for our health than setting them back? The shift to later morning light in the spring interferes with its valuable role in helping to set the body’s natural rhythms. Meanwhile, exposure to light later into the evening delays the brain’s release of melatonin, the hormone that promotes drowsiness. This causes us to sleep less overall, as noted by the BSS.
“Significant light exposure close to bedtime makes it difficult to fall asleep, through circadian mechanisms, but also via direct suppression of the sleep-promoting hormone melatonin and the direct alerting effects of light. Hence, the additional DST-induced delay of the already late sunsets in summer (relative to bedtime) makes it difficult to achieve a full night’s sleep in summer … Taken together, seasonal DST with its twice-yearly clock changes is likely suboptimal for sleep and circadian physiology, with potential risks for health and productivity.”
Personally, I love the change to DST. It’s great to have more time to spend outdoors. And although the scientific evidence is against a permanent change to summer time, it’s high time we moved to finally do away with our biannual changing of the clocks.
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