As millions of Australians prepare to lose an hour of sleep this Sunday, a major review suggests the health effects of daylight saving are far more mixed than its reputation suggests.
Australians bracing for the annual loss of an hour’s sleep this weekend may have less to fear than the warnings around daylight saving suggest.
Daylight saving begins on Sunday 4 October, when clocks move forward one hour.
The change applies in New South Wales, Victoria, South Australia, Tasmania, and the ACT, while Queensland, Western Australia, and the Northern Territory do not observe daylight saving.
The looming change is sure to bring debate across both sides of the daylight-saving issue – along with questions like: will it harm my health, will it confuse the livestock and, even, will it fade the curtains?
A major systematic review released earlier this year has challenged the idea that daylight saving and the twice-yearly clock changes are uniformly bad for health.
Researchers reviewed 157 studies from 36 countries examining the health effects of switching into and out of daylight-saving time (DST), as well as living under DST compared with standard time.
Their conclusion was that the evidence did not support widespread messaging that clock changes and DST during summer were uniformly detrimental to health.
The review, published in the European Journal of Epidemiology, included Australian researchers from Swinburne University of Technology, Central Queensland University, and the University of Western Australia.
The strongest adverse signal was cardiovascular.
Moving the clocks forward at the start of daylight saving was associated with a short-term increase in acute myocardial infarction, with the researchers estimating an approximately 4% increase in risk during the first one to four weeks after the transition.
However, there was no clear increase in all-cause mortality following the spring transition.
Traffic accidents also increased after the switch to DST in some locations, particularly fatal crashes in the US, although the finding was not consistent internationally.
But other commonly cited harms were much harder to pin down.
The researchers found no clear or consistent effect on psychiatric outcomes following either the transition into or out of DST. Fifteen studies examined psychiatric outcomes, including depression, bipolar disorder, mania, psychosis, and suicide, with the review assigning medium confidence to the finding of no clear effect.
The evidence for substantial disruption to sleep and circadian rhythms was also weaker than might be expected.
While sleep timing could shift after clocks moved forward, sleep duration did not appear to be consistently reduced at a population level. The researchers noted that some groups, including adolescents with early school start times, could nevertheless be more vulnerable.
The researchers said the finding raised questions about the often-proposed mechanism linking clock changes with adverse health effects.
Sleep and circadian disruption are frequently proposed as explanations for cardiovascular effects, but the review found either no effects or relatively small effects on sleep and circadian rhythms themselves, casting doubt on a simple causal relationship.
There were also potential benefits to daylight saving.
The transition back to standard time was associated with increased sleep duration and fewer workplace accidents, while one high-quality study found an approximately 2.5% reduction in all-cause mortality following the change.
Living with daylight saving during summer was associated with an approximately 4.5% reduction in all-cause mortality in one high-quality US study, while evidence from Chile suggested fewer traffic accidents under DST during parts of the year, the researchers found.
However, they cautioned against interpreting the findings as a clean bill of health for daylight saving.
Only about one in five of the 157 studies was rated high quality, study designs and outcomes varied substantially, and relatively few studies directly compared living under daylight saving with standard time at the same point in the year.
The Australian context also mattered. The researchers specifically noted that countries spanning wide ranges of latitude and longitude, including Australia, may experience different effects depending on location, cautioning against one-size-fits-all conclusions.
The researchers concluded that current evidence supported neither assumptions of uniform harm nor uniform benefit and called for more high-quality research alongside targeted strategies to reduce established risks around the clock changes.
“Whilst more high-quality studies are called for, the current evidence – acknowledging its limitations and the fact that health impacts are only one element of policy – supports a balanced approach: preserve potential benefits associated with DST, mitigate identified risks, and avoid assumptions of uniform harm or benefit,” they concluded.
“Policy decisions should weigh these uncertainties and prioritise targeted strategies to reduce adverse effects.”
As for the livestock and the curtains – neither rated a mention in the study. Watch this space.
