Why daylight saving time could be bad for you

Deirdré Straughan and Brendan Gregg love this time of year, when the clocks have moved forward to provide an extra hour of daylight in the evenings.

For the couple from Cronulla, daylight saving time means they can take full advantage of living near the beach.

“It gives us time to be more leisurely … we’ll go somewhere we can see the sunset around seven o’clock and then we’ll come back and have dinner after that,” Straughan says. “As the weather gets better, we’re able to do things like go swimming.”

Deirdré Straughan and Brendan Gregg love the lighter evenings and would prefer to have daylight saving time all year.Credit: Wolter Peeters

Originally introduced to save fuel in the two world wars, daylight saving time made a comeback in the 1970s and is now mostly seen as a lifestyle enhancement.

Clocks move forward in spring - on the first weekend of October in NSW, Victoria, Tasmania and South Australia - which means the sun appears to rise and set an hour later. Then in autumn - the first weekend in April - they move back. As the saying goes, “spring forward, fall back”.

But advances in medical research offer new evidence that daylight saving time could be harmful - and governments overseas are taking note.

Professor Ian Hickie, a psychiatrist and head of the University of Sydney’s Brain and Mind Centre, says there’s been an explosion in our understanding of “circadian rhythms” - the natural process regulating the sleep/wake cycle. In 2017 scientists working in this field won the Nobel Prize for Physiology or Medicine.

“The more we understand about the brain science of the whole area, the more people are going ‘hey, maybe we’ve made a mistake from a public health point of view’ [by having daylight saving time],” Hickie says.

He says there are two main problems with it. The first is the jetlag from changing the clocks.

Josh Hernandez is a keen astronomer and hates the change to daylight saving time in spring.Credit: Wolter Peeters

Hickie says this comes at the worst possible time because spring and autumn have the fastest changes to the length of daylight, so the human body is already working overtime trying to adjust.

The second problem is that the tradeoff for lighter evenings is artificially dark mornings.

Hickie says the human body is designed to sleep when it’s dark and morning light provides the best time to exercise - if sunrise is delayed, that opportunity is lost.

“If you could get up with the sun and then exercise a bit outside before work, you’d be better coordinated for the rest of the day, including mood, cognitive and metabolic; you’d be fitter and healthier,” he says. “I’m intrinsically more of an evening person so my chance of getting exercise in the morning or doing anything before work with daylight savings is nil.”

Some people, like Straughan and Gregg, would be happy if daylight saving time was year round even if it means getting up in the dark in winter.

Straughan struggles with the sudden change in autumn, especially when she worked in an office all day and found it was already dark when it was time to go home. She also does not feel safe exercising outside in the dark, a complaint echoed by many women, while Gregg says dark evenings make it hard to train for team sport.

Residents of Alberta, Canada voted in a referendum last month on whether to permanently stay on daylight saving time, rather than moving the clocks twice a year.

Albertans narrowly rejected the change, but several other Canadian provinces including Ontario, Saskatchewan and British Columbia are already dropping the “fall back”.

In 2019, the European Union voted to abolish the changing of the clocks; it was meant to end this year, with countries who wanted permanent summer time moving their clocks forward for the last time in March and those who wanted permanent winter time moving their clocks back for the last time in October. This effort has reportedly stalled because of disruptions caused by Brexit and COVID-19.

Professor Shantha Rajaratnam, a psychologist and chair of the Sleep Health Foundation, says it is not as straightforward as sticking to one time zone. The alignment to the planet’s dark and light cycle also matters.

Rajaratnam explains humans have three interacting clock processes. The first is the sun creating a cycle of light and dark, the second is the internal circadian clock of the body, and the third is the social clock that dictates when people should sleep, wake, eat, be active and socialise.

When clocks are naturally set to sun time, the sun is at the highest point at midday; during daylight saving time, the sun is at its peak at 1pm. (This can already vary within a timezone depending on whether you are near the eastern or western boundary).

Rajaratnam says daylight saving time effectively moves the social clock forward an hour, forcing the circadian clock to adjust.

“That’s a challenge for most people because the light and dark cycle hasn’t changed and the light and dark cycle is the major time cue that allows us to shift internal clocks when we travel across time zones,” he says. “It’s a form of jet lag, similar to people working shift work.”

Reducing exposure to morning light and increasing exposure to evening light also affects the circadian cycle by more than just the one-hour difference on the clock.

Rajaratnam explains that lighter evenings mean people don’t feel sleepy until later, with the effect lasting hours beyond sunset. That prompts people to stay up later and compounds the problem of feeling tired in the mornings.

Rajaratnam and Hickie note a host of health problems associated with circadian disruption - such as cardiovascular disease, metabolic problems such as diabetes and obesity, an increased risk of gastrointestinal conditions, and mental health conditions such as depression, anxiety, stress, and burnout.

“For this reason, many scientists in the field of circadian biology advocate for abolishing daylight saving time and retaining standard time,” Rajaratnam says.

Hickie says the end of daylight saving time would relieve parents who find it wreaks havoc with their children’s sleep schedules and benefit teenagers whose body clock naturally shifts to a later phase of going to bed and getting up later.

It would also be a boon for many adults such as Josh Hernandez, who detests daylight saving time.

While Hernandez enjoys staying up in the evenings, his hobbies don’t require daylight. He is into astronomy and has a telescope set up at home, but the best stargazing happens when it’s dark and all his calculations require true time.

The PhD student from Dural struggles to get up early in the mornings at the best of times.

“For me early is 9am, which seems to be a favourite for people to start work and suggest meetings,” Hernandez says. “For someone like me who has a bit of a later chronotype, more of a night owl, I find that a bit hard in general, and then I guess daylight saving time just exacerbates that.”

History of daylight saving time in Australia

1917: DST adopted to save fuel but abandoned the same year

1942-1944: DST reintroduced as wartime measure for three summers

1967: Tasmania introduces DST

1971: NSW, South Australia, Queensland and the ACT take up DST. Queensland soon drops it, before trialling it again for three summers from 1989/1990 to 1991/1992

1974: WA experiments with DST but dropped after a referendum in 1975. It is later reintroduced for three years from 2006

2007: NSW, Victoria, Tasmania and the ACT jointly commit to extend DST for an extra four to five weeks. SA later follows suit