How does daylight saving time affect your body clock?

“The scientific evidence points to acute increases in adverse health consequences from changing the clocks, including in heart health and strokes,” sleep expert Professor Adam Spira told the John Hopkins Bloomberg School of Public Health.

Evidence suggests the change is also associated with a heightened risk of mood disturbances as well as elevated production of inflammatory markers in response to stress.

The potential for car crashes also spikes just after the spring forward, Spira says. A 2020 study found that the switch raises the risk of traffic
accidents by 6%.

Another study in 2020 published in the Journal of Internal Medicine found that “human errors” among healthcare workers in the Mayo Clinic Health System increased by about 19% in the week after the springtime change compared to the week prior.

Errors included giving people incorrect medications or dosages, mislabelling laboratory samples and making mistakes during surgery.

Physical and mental health impacts are thought to be related to the impact of DST on circadian rhythms — the 24-hour body clock that is governed by light — by forcing it to follow an unnatural schedule until November when the clocks switch back to standard time.

“We function best when our sleep-wake cycle follows the sun. We get sleepy, due in part to melatonin release when it gets dark,” says Spira.

A study in Sleep (2022) suggested that moving the clocks forward in the spring results in going to sleep and waking up before our internal clocks are ready.

“This misalignment lasts for the duration of DST,” says Spira, adding it can reduce the amount of sleep we get to the detriment of our health.

Sleep deprived teenagers

Research published in the Journal of Clinical Sleep Medicine (2015) found that during school days after the time change, adolescent students were sleepier, had slower reaction times and were less attentive.

Teenagers face some of the greatest risks of sleep deprivation following the DST change because they already deal with chronic sleep issues during the school week, according to the American Academy of Sleep Medicine.

There’s a biological explanation too, according to Dr Beth Malow, professor of neurology and director of the sleep disorders division at Vanderbilt University Medical Centre, Tennessee.

Teens release their natural melatonin levels an average of two hours later than adults because their body clocks shift to a later period during puberty. So, when DST comes around, their already altered sleep becomes more disrupted, aggravated by busy social lives, school schedules and part-time jobs.

Why does pushing the clock forward by one hour in the spring have such an impact on physical and mental health?

The key is the disruption that DST causes to your circadian rhythm.

These rhythms are a complex interaction of genes, enzymes and hormones that control your daily fluctuations in an array of body functions that include mood, appetite, digestion, blood pressure and blood sugar.

Just about every tissue, organ and cell in your body has an internal clock. So, pushing the clock forward an hour can impact those complex body clocks, an impact that can last for weeks or even months.

DST disrupts our social clock which dictates when we go to work, school and socialise.

Our biological clocks can’t always keep up with the change.

The result is what scientists call ‘circadian misalignment’ or ‘social jetlag’. The evidence suggests that some people struggle more than others, particularly those with sleep disorders, jobs with inconsistent hours, or mental health problems.

Time change disrupts body clock

Malow told Buzzfeed News (2022) that no matter who you are or what you do for a living, your body clock never really adjusts: “You could say you adjust to the sleep loss in a few days, but from a circadian alignment standpoint you’re really off the whole period of time. There’s a mismatch between what’s going on with the light and what’s going on with our bodies. It kind of jars the system in a way that just moving time zones might not.”

Changing the time disrupts our body clocks. For most people, changing the time — even if only by one hour — may produce tiredness as a small inconvenience.

Other people can have more serious consequences. Prioritising sleep around the start of DST can smooth the transition.

Malow suggests going to bed a little earlier (about 15 to 20 minutes) two to three days before the switch to DST. Other measures include starting daily routines that serve as time cues for your body a bit earlier in the days before the DST switch.

Healthy sleep habits include getting seven to nine hours of rest a night; keeping your bedroom dark and cool; and avoiding caffeine or alcohol before bed.

Benjamin Franklin invented the concept of DST in 1784, believing rising earlier would economise candle usage and save money. Is it finally time to change this outdated concept?

• Dr Catherine Conlon is a public health doctor in Cork and former director of human health and nutrition, safefood.