Daylight Saving Time (DST) is the practice of setting the clocks forward one hour from standard time during the summer months and back again in the autumn (fall) to make better use of natural daylight.

Many regions and countries are reconsidering their use of DST, but their approaches differ. In the Australian summer, New South Wales, Victoria, South Australia, Tasmania and the ACT turn their clocks forward one hour to DST. Daylight Saving Time begins at 2 am (AEST) on the first Sunday in October and ends at 3 am (Australian Eastern Daylight Time) on the first Sunday in April.

An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity. Although energy conservation remains an important goal, energy usage patterns have significantly changed since then. In the United States, daylight saving time was first used in 1918 when a bill introduced a seasonal time shift. Australia’s first observance of DST was in 1916. 

What are the advantages of daylight saving?

During DST we finish work earlier with more sunlight hours remaining for leisure time after work and this has great advantages:

  1. More physical activities with positive effects on health
  2. More bonding time with loved ones that is good for mental health.

Activity increases with more extended evening daylight, but interestingly these results are culture-specific: a significant increase is mainly observed in Europe and to some extent in Australia, while no significant effects or even slightly adverse effects are seen in the United States and Brazil.

DST also saves energy since we don’t use our lights as much in the evening. In addition, it reduces road accidents because people are less likely to be driving in the dark, plus it decreases crime rates.

But what are the costs?

Whilst here are good sides to DST, such as coming home earlier, shifting the clock back 1 hour is the same as shifting your entire schedule 1 hour later or travelling 1 time zone to the west. Changing the time, even if it is only by an hour, disrupts our body clocks and rhythm.

People who have difficulty sleeping can get anxious about changes to their sleep routine. They may have meticulous habits around sleep that they put in place to minimise the impact of day to day variations on sleep. When changes like DST happen, changes to their routines are forced upon them and it can result in sleep-related anxiety.

It is important to note that DST transitions can elicit short and long-term effects, which we will refer to as acute and chronic effects, respectively. The first days after the DST change in spring show acute effects:

  • Sleep is shortened
  • Adolescents are sleepier during the day
  • General accidents and visits to the emergency room increase, so do myocardial infarctions (heart attacks) and strokes
  • Risk of in-vitro fertilized (IVF) mothers losing their babies
  • Suffering from negative mood changes

On the other hand, there are very few reports on the chronic effects of DST. These are difficult to study as comparisons between DST and Standard Time are usually confounded by seasonal effects. The chronic effects may be minor on an individual level, but they can accumulate over time and both across time and space in populations resulting in much bigger impact, the costs of which are often hidden and hard to measure. There are also significant financial costs to communities of DST. Timetables need to be adjusted particularly when travelling across timezones or between states or countries. 

So should we get rid of daylight saving?

From an overall population health perspective, the circadian misalignment that occurs as a result of DST has significant effects. It is not clear whether these effects are outweighed by the positive effects of greater social interaction from having more daylight hours in the evening during summer months. DST is also popular, so it would be a brave government that abolished DST.

If you are interested in a more detailed discussion of the pros and cons of DST and impacts of changing ‘social time’ listen to this podcast interview with Prof Till Roenneberg.

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