As we approach the end of March, many countries around the world from Mongolia to Paraguay to Greenland are preparing to ‘spring forward’ and move the clocks forward an hour. Each year, Daylight Savings Time (DST) brings with it passionate debates about whether it should be scrapped or retained. And in 2019, EU member states voted to stop observing DST from 2021 – making this (possibly) the last year that seasonal time change will be observed in Denmark.

The clocks at the Gare Saint-Lazare in Paris are changed to daylight savings time in 1937, Wikicommons.

Chronobiologists (people who study circadian rhythms) have become interested in the effect DST has on our circadian system. In recent decades, scientists have discovered how important our internal body clocks are to our overall health. Setting our internal time in response to external environmental cues (like light or food), the clock genes in our cells help make sure our complex bodily processes run on time and in the right order. Disrupting this order, called de-synchrony, can have serious long-term health effects, including metabolic syndromes like diabetes as well as sleep disruption and even affecting mood and psychiatric disorders. It seems then that forcing our body clocks to move forward or back an hour twice a year might be a problem for our circadian health. Its effects have been described by chronobiologist Till Roenneberg as ‘social jet lag’: when our body clocks are out of sync with the world around us. If DST is so damaging, why exactly have we been tinkering with the clocks on and off over the last 100 years? And did anyone ever think it was good for our health? To answer that, we must go back in time to the original daylight savings time proposals and to the debates that surrounded the first Daylight Savings legislation in the United Kingdom in the first decade of the twentieth century.

Diagram showing the mechanism of the brain which sets our body clocks. Wiki Commons.

One warm summer morning, an English architect named William Willett (1856–1915) awoke early and prepared to take his morning horse ride. While living in a fashionable corner of London, he could enjoy the streets practically to himself at 7am. He was suddenly struck with inspiration – wouldn’t it be better for everyone to get up early and enjoy themselves while the days are long? Wouldn’t it be healthier for people to get more exercise? And why do we spend so much money on artificial light in the evening when we could just start working earlier?

While Willet is remembered as the founder of modern daylight savings time, he wasn’t the first to have the idea. In fact, American diplomat Benjamin Franklin (1705–1790) had the same idea over a hundred years earlier. One morning while serving as the American ambassador to Paris, Franklin was awakened unusually early (6am) by a loud noise. Much to his surprise, he found the sun streaming in the curtains. It was a shock to Franklin, who wrote that he often did not get out of the house until noon (although one can expect that such a luxurious lie-in was not possible for most Parisians). Like Willett, Franklin suggested that early rising in the summer would be productive and economical, saving on expensive candle light.

Franklin’s plan involved forcing all of the church bells to ring simultaneously as soon as the sun rose and firing off canons for good measure but Willett had a more subtle approach – to simply change the clock. As Willett observed, clock time was a human invention anyway – surely it was better to live closer to the time of the sun. Because of the tilt of the Earth and the shape of the axis around the sun, clock time only correlates directly with solar time a few times a year. With Willett’s plan people would carry on their daily schedules just as usual – the only change would be that the clock hands would read something slightly different.

A young woman takes down the curtain revealing the daylight. Wellcome Collection.

 In 1907, Willett published a pamphlet called The Waste of Daylight where he announced his plan to move the clocks back by 20 minutes over four weeks each April and return them slowly each September. He reasoned, “If one of the hours of sunlight wasted in the morning could be added to the end of the day, many benefits would be gained, especially by those who would spend in the open air, whatever time they might have at their disposal after the duties of the day have been discharged. ‘ [1]Willett estimated that the country would save £ 3 million a year on lighting and that each person would gain an entire year of daylight over their lifetimes. Endorsed by industrialists, physicians, shop assistants, and financiers – Willett’s pamphlet prompted the British Parliament to launch a special committee investigation into whether the country should adopt the plan as law in the spring of 1908.

Willet and his supporters offered many reasons why daylight savings (or summer time) would be beneficial. The most important, of course, was “to reduce the industrial, commercial and domestic expenditure on artificial light.” [2]While we often think of DST as related to industrial efficiency, in original discussions, the health of the population was a far more important factor. Of the six main effects the new Daylight Savings Bill was proposed to have, five of them related to the improved wellbeing of the British public. An extra hour of daylight after work was felt to be an ideal opportunity for people of all classes to get extra time to play and exercise in the sun after the workday was through. This would result in greater health and happiness, and even provide the opportunity for more young men to get involved as volunteers in the British Army. What’s more, being technically an hour earlier than usual, there would be less time for people to go drinking in the pub – which they were less likely to do anyway while the sun was out.

A dentist jokes about the double meaning of ‘gas’ arguing daylight is best for undertaking an extraction. Wiki Commons.

The essential principal behind the act and its health benefits was the prevalent early 20 th century belief at de sun was essential two health. Sun therapy was widely used to treat conditions like tuberculosis and rickets. Patients lived in open-air sanatoria and were encouraged (often forced) to socialize, exercise and even sleep outside to obtain the healing benefits of sun and fresh air. In 1903, Danish physician Niels Finsen had won a Nobel Prize for demonstrating that intense and focused light therapy could be used to heal skin diseases like lupus vulgaris. In 1910, one journalist summarized, “light is literally life.” [3]

The need to give the British working classes the healing power of light had never been more pressing than in the early 20 thcentury. The UK had just lost an embarrassment in South Africa – shattering the colonial fantasy that the British race were naturally superior to the people they dominated around their empire. The loss brought into sharp relief the poor physical condition of the British working classes – poor teeth, failing eyesight, the prevalence of disease and a lack of physical strength were associated with a physical and moral ‘degeneration’ of the British race (unfortunately often blamed on the laziness and carelessness of the people themselves, rather than systematic poverty and poor housing conditions). Daylight savings time seemed a simple and effective way to provide more opportunities for sun exposure, outdoor exercise, and to keep tired eyes from being damaged by dim candle or gas light.

Children participate in outdoor exercise at a sanatorium, early 20th century. Wellcome Collection.

One particular group was believed to benefit particularly from the new regulations: shop assistants. Britain has been called a ‘nation of shop keepers’ and by the end of the nineteenth century saw a boom in the commercial industries. But shop assistants often face poor working conditions – working long hours will take few breaks and only a few short minutes for meals (which often had to be taken in cramped back rooms). Often staying until 10pm or midnight, shop assistants (many of whom were women) rarely saw the sun and were left with almost no time for education or religious betterment. Shop workers and clerks also faced high levels of respiratory diseases, such as tuberculosis. ‘The misery and suffering, together with the physical, mental and moral deterioration involved, constitute an evil of the worst kind,[4] An extra hour of sunlight in the evening was proposed as a helpful way of improving the lives of this group of people, who had received a considerable amount of attention in the lay and medical press. Physician to the King Sir Thomas Barlow went so far as to propose that an extra hour of sunshine would go a considerable way to healing the anemia and respiratory diseases which seemed to be rife among shop workers. ‘You gain to stand by sunshine all along the line,’ he concluded. [5]

Shop Girls by William Gacken, 1900, Metropolitan Museum of Art.

But as much as the hour change might help the shop assistants, there were many more workers who it was likely to harm. In particular, staff members of the British post office were against the bill. Many already had to wake up at 4 or 5 in the morning to start shifts as postmen or sorting letters – and some even had to work over night shifts to keep the mail running on time. Barlow testified to the committee that at 4am the body’s vitality was at its lowest – and rising at this time of day, or working the night shift, could have serious health consequences. Similarly, British factory workers started shifts at 6am working until 6pm. Most disadvantaged were the farmers, who worked in the light of the sun anyway and could not start their tasks any earlier: many already began their days at 3am. Hawkers in the city’s fruit and vegetable market at Covent Garden started their working days at 2am. Rising any earlier, by the clock or by the sun, seemed a physical impossibility.

Ultimately, the decision on whether to continue with the Bill was not based on health concerns. From the testimony provided to the parliamentary committee, it is clear that no one questioned the physical benefits of the change (except perhaps for night shift and farm workers – who would be forced to work at an unhealthy hour of the night). Of much greater concern was the effect that the change in time would have on the delivery of international mail, on the running of the railways and on international business (closing the stock market an hour early, for example). Naturally, there were many who simply thought the idea of ​​changing the clocks was preposterous in the first place. The UK’s Astronomer Royal joked that if they were to put the clocks back an hour, why not make the thermometers 10 degrees summer so everyone could enjoy hotter weather.[6] The DST Bill was ultimately not passed by the British Parliament in 1908 or even during another attempt in 1909. In fact, Britain did not implement daylight savings time until the First World War – and this likely in response to the fact that Germany had already put in place a time change plan to save on artificial light and to allow munitions factories to work later.

Pro-daylight savings cartoon from the United States c. 1930s, Wikicommons.

Daylight Savings Time was implementeres on and off around the world across the 20 th century – fortrinsvist in response two outbreaks of war or shortages of energy. New transportation technologies like airplanes and the rise in the use of cars made the change of hours more complicated and more disruptive than ever before. By the 1960s, it was becoming apartment that the changing time was associated with increased motor-vehicle fatalities. In the United States, it was particularly concerning that a significant number of these car accidents involved the death of young children walking to school on the now much darker morning. Nevertheless, by the 1980s, most countries in Western Europe had returned to the use of DST.

Unfortunately, there have been very few studies that examine in depth the physical and mental effects of our yearly time change. Some scientists have pointed out that it is actually much harder for our bodies to re-synchronize our clocks after the hours’ time shift – because despite traveling to a new time zone, the sun is still rising and setting at the same time, even though the clocks have changed. This means it takes longer for our body clocks to re-adjust. [7] On average, it takes our bodies about 5 days to sync up to the new time. Clock misalignment can have very serious health effects and studies have shown a higher incidence of cardiovascular events such as heart attacks after a spring DST change. [8]Although larger studies have been needed, many circadian biologists and physicians believe the likelihood of negative effects on our circadian health means we should do away with DST.

While DST is on its way out in Europe, EU member states will still have an important decision to make. Do they decide to stay at constant winter (standard) time or constant summer time? Environmental health specialists have advised that constant summer time would be highly preferable to maintaining standard time as the morning daylight acts as a ‘zeitgeiber’ to set our master clock. [9] Getting enough morning sun not only means our clocks are synchronized with our environment, but it can also help with seasonally effective disorders and some other forms of depression. However, others argue that our body clocks are able to adapt to the constantly changing dawn only during standard time and not summer time. [10]The choice we make now could have a significant impact on our health in the future. Only time will tell.

Note: This blog was written prior to the COVID-19 crisis. However, daylight savings time observation will continue at 2am on Sunday the 29th of March. Maybe we can see it as a reminder of how life continues on – or at least, an hour less time in quarantine?


[1] William Willett. The Waste of Daylight. Text of the Daylight Savings Bill. Opinions of Eminent Men. Statement of Progress . (London: Privately printed, 1914).

[2] David Prerau, Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time (New York: Thundermouth Pres, 2005).

[3] “The Coming of the Sunlight: Influence on the Nation’s Health”, The Times (London) , 1910, Supplement.

[4] Thomas Sutherst, Death and Disease Behind the Counter , (London: Kegal Paul, Trench and Co., 1884).

[5] Report and Special Report of the Select Committee on the Daylight Saving Bill … (London: Wyman and Sons, 1909).

[6] Michael Downing, Spring Forward: The Annual Madness of Daylight Savings Time , (Washington DC: Shoemaker and Hoarde, 2005).

[7] Fler e Cruz et al., “Impact of Daylight Saving Time on Circadian Timing System,” European Journal of Internal Medicine 60 (2019): 1–3.

[8] Manfredini et al., “Daylight savings time and myocardial infarction,” European Review for Medical and Pharmacological Sciences 22 (2018): 750–755.

[9] Ekmekcioglu et al. ‘Let the morning sunshine in’, The Lancet 394 (2019), 1518.

[10] Roenneberg et. eel. ‘Why should we abolish daylight saving time?’ Journal of Biological Rhythms 34 (2019), 227–230.

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