How moving the clock forward this weekend could kill you

Dr Muiris Houston: Seems like there is a strong argument to stop our clock tinkering

Why don’t the same health risks apply when we travel to mainland Europe and ‘lose’ an hour as we move from Irish time to Central European Time?

On Saturday night you will lose one hour of sleep as we transition to daylight saving time (DST). For many, it’s worth it for the sudden infusion of an extra hour of daylight in the evening time. But for others, it could be the the reason they develop a life-threatening illness in the days after the chronological tinkering.

There is an increasing body of evidence to suggest that the sudden clock change is bad for our health. During the first days after the change, many people suffer from symptoms such as irritability, less sleep, daytime fatigue and reduced immune function. More worryingly, heart attacks, strokes and workplace injuries can happen during the first weeks after a clock change compared with other weeks. There’s also an increase in fatal car crashes in the week we “spring forward”.

Why is 'springing forward' so hard on the body? It's because our clock time is moved an hour later

Dr Beth Ann Malow is a professor of neurology and paediatrics at Vanderbilt University Medical Center in Nashville, Tennessee. In an article for the journal JAMA Neurology, she and her co-authors reviewed the evidence linking the annual transition to daylight saving time to increased strokes, heart attacks and teen sleep deprivation. "Based on an extensive body of research, my colleagues and I believe that the science establishing these links is strong and that the evidence makes a good case for adopting permanent standard time," she says.

Separately, scientists in the US and Scandinavia used the electronic health records (EHRs) of hundreds of millions of people across the US and Sweden in order 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).


Daylight saving time was first implemented during the first World War. 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 in winter.

Why is “springing forward” so hard on the body? It’s because our clock time is moved an hour later; in other words, it feels like 7am even though our clocks say it is 8am. So it’s a permanent shift to later morning light for almost eight months – especially notable because morning light is valuable for 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 can interfere with sleep and cause us to sleep less overall.

All of which upsets the circadian rhythm of our internal biological “clock”. 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 a 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.

And why don't the same health risks apply when we travel to mainland Europe and "lose" an hour as we move from Irish time to Central European Time? According to Malow, it's because in flying from one time zone to another, we are changing our clocks as well as our environment. "The environmental time cues, such as sunrise and sunset, help our bodies adjust."

All in all, it sounds like there is a strong argument to stop our biannual clock tinkering. What do you think?

mhouston@irishtimes.comOpens in new window ]