With New Zealanders preparing to turn their clocks back as daylight saving ends this Sunday, I’ve been pondering the history and science behind this tradition.

Like many New Zealanders, I have a love-hate relationship with daylight saving.

I hate losing sleep when the clocks ‘spring forward’ in September and I hate biking home in the dark when they ‘fall back’ in April. I hate having to remember to change my clocks and, in the case of my car and oven, sometimes don’t even bother.

But then again, as an April baby, I love that every so often my birthday is 25 hours long. And I love the twice yearly reminder that, while of course our clocks are designed based on the rotation of the earth, our systems of time are ultimately made up and can be changed at will.

So where did this time-turning traditional come from anyway?

There have long been proponents of daylight saving, from Benjamin Franklin (somewhat satirically) in 1784 to New Zealand’s very own G.V. Hudson, an entomologist and one of the first heads of the Royal Society who reportedly wanted more time to hunt for insects after work. Daylight saving eventually became a reality when Germany’s clocks sprung forward an hour in an effort to conserve energy and provide more usable daylight hours during WWI, soon followed by the UK, France and the US. Today, some form of daylight saving is observed in about 70 countries, mostly those closer to the poles, where the tilt of the earth means seasonal variation is greatest.

As explained by Keith Lynch and Kate Newton in Stuff, daylight saving didn’t reach Aotearoa until 1928, when clocks were moved forwards an hour between November and March. Over the next ten years, adjustments were made, including reducing the ‘spring forward’ to 30 minutes and changing the days of the biannual ritual. In WWII, daylight saving time was made permanent, giving us what’s now our ‘standard time.’

We then spent close to three decades without adjusting the clocks, until a global energy crisis in the 1970s saw the tradition come back, again with the justification being less energy use in the longer summer evenings. Since then, the period of daylight saving has been extended twice, the justification has shifted from energy saving to recreational benefits, and the whole ritual has garnered plenty of debate. 2008 polling, from the last time the daylight saving window was increased, found the extension was popular with 82% of New Zealanders overall, but just over half of farmers, who tend to rise early for work and benefit less from an extra hour of sun at the end of the day. For now, the Department of Internal Affairs (which administers the governing legislation) doesn’t plan to make any further changes.

And yet this history of playing with the clocks shows that the biannual clock change isn’t an inevitability. Indeed, last year the Fiordland town of Te Anau announced plans to reject the autumnal ‘fall back,’ instead adopting permanent summertime hours in an effort to attract tourists. Back in 1984, the Northland dairy farming community of Ararua rebelled in the other direction, rejecting the ‘spring forward’ to reduce time spent milking in the dark.

There are plenty of opinions on daylight saving, but what about the science?

It’s relatively well established that the act of shifting the clocks forward in Spring causes lost sleep and reduced sleep quality in the following days or even weeks, and can be associated with delayed reaction times, lapses in vigilance, and increased daytime sleepiness. In addition, while we often talk about gaining an hour of sleep when the clocks move back in Autumn, there’s little evidence to suggest that this is actually the case, with our body clocks taking time to adjust.

Changing the clocks is associated with negative wellbeing impacts beyond sleepiness. A Finnish study found a small but significant increase in the risk of being hospitalised for ischemic stroke in the first two days after a clock change in either direction. And a meta-analysis found that heart attack risk is modestly elevated in the weeks following the ‘spring forward.’ While an increase in traffic accidents following clock shifts is often cited, the evidence on this is patchy and sometimes conflicting, and it’s hard to disentangle confounding factors like the impact of public holidays coinciding with clock changes.

If we did decide to stop changing the clocks, we’d then have to work out whether to stick with standard time or daylight saving time. The US is currently working towards the latter, with the ‘Sunshine Protection Act’ recently passed by Senate, although it still needs to pass through the House and be signed off by the President before it becomes law.

As part of the legislative process, three witnesses provided testimonies to the relevant Congress committee, one firmly in favour of permanent daylight saving time, one firmly in favour of permanent standard time, and the other happy with the status quo or an extension of daylight saving time. All had pretty sound reasons for their positions. The witnesses in favour of daylight saving time pointed to evidence suggesting lighter evenings lead to fewer road traffic incidents, reduced crime, more recreation and commerce, and energy saving (although this last point is disputed). The witness in favour of standard time (as well as the American Academy of Sleep Medicine) argued that standard time is more in line with our body clocks and would help with alertness in the mornings, including for school kids, who would start school in the dark in winter under a permanent regime of daylight saving.

It’s complicated out there. There’s certainly agreement that there are negative impacts associated with shifting the clocks, but the debate about whether permanent standard time or permanent daylight saving time would be better than the status quo, and which permanent time regime is superior, is far from settled.

Ultimately, it’s possible to make a case in any direction. While more evidence on the pros and cons of different time regimes would be helpful, the daylight saving debate, like so many others, is about both facts and values. There will always be proponents on all sides, with positions varying depending on who you are, where you live, and what you value. Are you a morning person or an evening person? Do you live in the upper North Island or the lower South? Do you like fireworks or sunrises? Do you work inside or outside? Do you have young children or not? And so on.

After all this pondering, my love-hate relationship with daylight saving lives on. On Sunday 3 April, as we collectively turn our clocks back (except you, Te Anau), I’ll be mourning the disruption to my body clock, reflecting on how weird time is, and, yes, celebrating the fact that the clock in my car will be correct for the first time this year.

Ngā mihi,