Why your chronotype affects how your body and mind reacts to daylight saving

The clocks have been turned forward an hour, but your body is probably still playing catch up.

While an hour might not sound much, it can have a big impact on our body clocks, which in turn can affect everything from digestion to blood pressure.

In fact, it’s been suggested that it would be better for our health if we did away with seasonal clock changes altogether.

Earlier this year, the American Academy of Sleep Medicine called for the twice-yearly clock changes to be scrapped on the basis that it causes misalignment between the outside world and our body clock, or circadian rhythm, stating that this “has been associated with risks to physical and mental health and safety, as well as risks to public health”.

The good news is there are steps you can take to minimise such disruption.

Research has long shown that daylight saving time is linked to a sharp rise in health problems such as heart attack and stroke, as well as hospital admissions for atrial fibrillation (an irregular heart rate) in the days after.

And a 2019 review of seven previous studies by the University of Ferrara in Italy, suggested that it’s the disruption of our circadian rhythms and lack of sleep that lead to raised heart rate, blood pressure and levels of inflammation.

The two clock changes every year have also been linked to an increase in road traffic accidents, possibly as the disruption to sleep and our body clocks leaves us feeling “jet-lagged” and less alert.

For example, a 2020 study in the journal Current Biology found a 6 per cent rise in car accidents following the springtime change, while a 2018 RAC review of police data suggests there is a surge in road traffic accidents after the clocks “fall back” to standard time in October.

“Every cell of the body has its own clock,” explains Dr Gisela Helfer, assistant professor in physiology and metabolism at the University of Bradford.

“We also have a master clock in the brain – the suprachiasmatic nucleus (a tiny cluster of nerve cells) – and what this does is coordinate those rhythms, like a conductor in an orchestra.

“Every physiological process has a specific time where it works best. For example, when we sleep we aren’t eating, so we don’t need as many hormones to help us with digestion.

“But when we wake up and our bodies are expecting to break our fast, we need insulin and for the whole gastro-intestinal tract to be prepared for the food that’s coming.

“The problem is our brain resets quickly to the new time, but our tissues and organs – such as our digestive system – have to catch up. We are then out of sync for a week or two, and that’s when you experience this feeling of jet-lag.”

A study in the Journal of Clinical Gastroenterology in 2020 suggested that a disrupted circadian rhythm can cause stomach issues, most notably constipation.

The change in sleep patterns can also trigger migraine or headache.

To manage the UK time transition happening later this month smoothly, Dr Kat Lederle, a sleep specialist from The London General Practice, suggested that in the six days before the clocks go back in autumn, people should go to bed maybe ten minutes later progressively each day.

In the spring, they should do the opposite. The advice would be similar in Australia when the clocks change.

“And do the same with meal times and anything else you can shift in small steps [e.g. a training schedule],” she adds.

This helps because the timing of our meals and exercise send cues to our body clocks that help them stay in rhythm.

But why is a time change of just an hour so disruptive in the first place?

It’s to do with changing light levels.

Our bodies need dark in the evening to help them prepare for sleep by producing melatonin, whereas light does the opposite.

Daylight directly signals the “master clock” via special light-receptor cells in the eyes, which the body takes as its cue to suppress melatonin, as well as signalling to the other clocks in our body that they need to be on daytime mode.

Clock changes may also affect us differently according to our “chronotype” – that is, our genetic propensity to be a lark (early to bed, early to rise) or an owl (late to bed, late to rise).

Larks seem to struggle with the autumn change more than the spring shift, according to a 2007 study by the University of Groningen, in the Netherlands, published in the journal Current Biology.

But owls and people who aren’t strongly one chronotype or the other find spring harder.

While you might think the evenings getting darker earlier would be better for larks, they find it harder to adjust – possibly because they don’t feel the benefit of the lighter mornings, as they’re up before dawn anyway.

And they’re unlikely to enjoy an extra hour in bed.

Others who are unlikely to get the benefit of the bonus hour of sleep with the autumn clock change include anyone sharing their home with beings whose brains don’t understand the concept of clock time: namely babies, dogs and cats.

That is, unless you also make an effort to gradually adjust light exposure and feeding times beforehand.

However, the good news is babies adapt quicker to “falling backwards” (and have fewer night-time wake-ups after the clocks go back), reported the journal Sleep in May last year – this is possibly because standard time is a better match with our natural circadian rhythm.

Which has all fuelled debate over whether we should stick to one time all year round.

In 2022, the American Medical Association called for an end to daylight saving, saying:”‘Committing to standard time has health benefits and allows us to end the bi-annual tug of war between our biological and alarm clocks.”

Dr Lederle agrees: “When we suddenly have this mismatch, our brain gets confused as to what process should be triggered and what should be stopped.

“That’s when we see an increase in health conditions – it affects heart rate, blood pressure and digestion, and long term we see an association between disrupted clocks and cancer risk plus fertility risk for women.”

And while some modern proponents suggest picking one or the other “100 per cent, I would stick with standard time’, says Dr Lederle.

“It doesn’t feel like it, because the days are shorter, but it is the healthier one of the two. It’s better for our sleep.”