Daylight Savings Time:

Jacob Schor ND FABNO

November 20, 2008

This time of year the short days and long nights get to me.   It’s a rare year though as Chanukah falls astride both the Solstice and Christmas; I’m looking forward to lighting candles and the hope and promise they bring.

It’s not often that the lunar and solar calendars line up this way. This leads me to ponder the systems we have created to track the passage of time.  Several recent publications have me thinking about Daylight Savings Time (DST) in particular.  The rationale used to justify DST has slipped away and published data suggests that DST may be detrimental to our health.

Benjamin Franklin is given credit for being the first to suggest DST. This stems from a letter Franklin wrote while living in Paris in 1784 in which he half-jokingly calculated how much money might be saved if people were to wake earlier in the morning. At the time the fashion was to stay up late and sleep through the morning, at least the crowd Franklin was hanging out with did. His math suggested the 100,000 inhabitants of Paris could save 64,050,000 pounds of candle wax over a 6-month period. Franklin as always was ahead of his time.

Before we consider DST we need to back up and remember that the concepts of standard time and time zones are relatively recent inventions.  Because we have lived with these arbitrary arrangement all our lives we take them for granted. 

As the earth rotates on its axis, the sun appears to move across the sky.  Noon is when the sun reaches its daily zenith, the highest point in the sky; once upon a time this was when the clocks were set to 12:00.  Local time varied along latitude lines paralleling the equator.  The further west you went, the earlier in the day it was.  The sun arrives later in Vail than in Denver.   The sun sets in Chicago long before it does in Denver. Every town had its own town clock and operated on its own time.  This worked fine when people traveled by foot.

Building the railroads messed this up and created the need for standard time, that is all clocks in all towns set to the same time.  Without a common time how could trains run on schedule?  Britain was the first to use a standard time. Dr. William Wollaston (1766-1828) is credited with coming up with the idea that was then popularized by Abraham Osler (1808-1903). The Great Western Railway was the first to adopt London Time and by 1847 most British railroads had done the same.  By 1855, most clocks in Britain were set to Greenwich Mean Time (GMT) though the legal system held out and didn’t adopt GMT until 1880 causing all sorts of curious peculiarities that seem perfectly suited for the British to have tolerated.


William Lambert first proposed time standardization and time zones in the U.S. back in 1809.  Yet his idea wasn’t adopted until 1883. Detroit held out, keeping a local time, 28 minutes later than Central Standard Time, until 1900.

Daylight Savings Time:

During the First World War, Germany and Austria initiated DST on April 30, 1916, moving their clock hands one hour ahead to conserve energy. The rest of Europe, Canada and Australia immediately copied the Germans. The U.S. held out until 1918.  DST was unpopular in our country and was repealed in 1919.

Roosevelt re-instituted year-round Daylight Saving Time from February 1942 to September 1945. It was a free for all from 1945 to 1966 with states and localities making their own decisions whether to observe DST. Confusing?  You bet, especially for TV, radio, trains, and airlines.

In 1974, Nixon signed into law the Emergency Daylight Saving Time Energy Conservation Act and implemented the Daylight Saving Time Energy Act setting clocks ahead. Congress amended the Act, and Standard Time returned in October 1974. Daylight Saving Time resumed on February 23, 1975 and ended on October 26, 1975. Looking back it all appears rather arbitrary, almost chaotic.


These days in most of the United States Daylight Saving Time begins at 2:00 a.m. on the second Sunday in March and reverts to standard time on the first Sunday in November.

There are problems coming to light with this entire DST business.  First off it’s dangerous and second it doesn’t ‘save’ anything. 

In 2004 the Journal of the American College of Cardiology published an article on the ‘Effect of sleep loss on C-reactive protein, an inflammatory marker of cardiovascular risk.’  In simple terms missing sleep triggers an inflammatory reaction, a reaction that we now know increases risk of having a heart attack or stroke.

When we shift into and out of DST we disrupt our circadian clocks.   Actually it’s more complicated than that.  Although work and school schedules follow the clock, biological rhythms stick with the sun and don’t adjust like we pretend they do.    Messing with internal clocks is trouble.  Even waking on time for work on Monday mornings is a problem.

Back in 2005 the European Journal of Epidemiology reported that men were more likely to have heart attacks on Mondays than any other day of the week. “The odds ratio (OR) of sudden cardiac death on Monday compared to other days of the week was 1.20 ….. The excess mortality due to the Monday peak amounted to 4.9 per 1000 deaths. The Monday peak was more pronounced in non-hospitalised ….. than in hospitalised patients …..”

So when you feel like everything is an up hill slog through mud on a Monday morning, well, your heart agrees with you.


Real concern about DST started, just before over our most recent ‘time shift’  when, on October 30, the New England Journal of Medicine published an article, “Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction.”   Imre Janszky of the Karolinska Institute carefully evaluated Swedish medical records and found, “The incidence of acute myocardial infarction was significantly increased for the first 3 weekdays after the transition to daylight saving time in the Spring…. In contrast, after the transition out of daylight saving time in the autumn, only the first weekday was affected …..” 

Jansky explains this phenomenon; “The most plausible explanation for our findings is the adverse effect of sleep deprivation on cardiovascular health. According to experimental studies, this adverse effect includes the predominance of sympathetic activity and an increase in pro-inflammatory cytokine levels.  Our data suggest that vulnerable people might benefit from avoiding sudden changes in their biologic rhythms.”

“… people in Western societies are chronically sleep deprived, since the average sleep duration decreased from 9.0 to 7.5 hours during the 20th century.  Therefore, it is important to examine whether we can achieve beneficial effects with prolonged sleep.”

Noting the prior reports of  higher infarction risk on Mondays  were explained as simply associated, “with the mental stress of starting a new workweek and the increase in activity,”  Jansky provides another explanation,  “… that there is another, sleep-related component in the excess incidence of acute myocardial infarction on Monday. Sleep-diary studies suggest that bedtimes and wake-up times are usually later on weekend days than on weekdays; the earlier wake-up times on the first workday of the week and the consequent minor sleep deprivation can be hypothesized to have an adverse cardiovascular effect in some people. This effect would be less pronounced with the transition out of daylight saving time, since it allows for additional sleep.”

Sleep deprivation and attempts to suddenly shift circadian rhythm create inflammatory reactions in the body makes sense.  That these changes can be measured in mortality still is surprising.


Though this association with DST and heart attack risk is new, safety experts knew already to expect increased car accidents during shifts both into DST in the spring and out of it in the fall.

While it is becoming clear that DST isn’t good for us, the rationale that DST saves energy and money has also been undermined.  In an op-ed piece in the November 20 New York Times Matthew Kotchen and Laura Grant from the university of California, Santa Barbara, talk about their research that disproves this idea. In Ben Franklin’s time it was relevant to calculate candle wax spared from using “sunshine rather than candles” but his calculations no longer hold.

Kotchen and Grant conducted “a study in Indiana, where daylight time was instituted statewide only in 2006. Before that year, daylight time was in effect in just a handful of counties. This change of policy offered a unique, natural experiment to measure the overall effect on residential electricity consumption.” 

They found, “that daylight time caused a 1 percent overall increase in residential electricity use….. Daylight time costs Indiana households an average of $3.29 a year in higher electricity bills, or about $9 million for the whole state.”

Why such an increase?

“…[while] daylight time reduces demand for household lighting, it increases demand for heating in the early spring and late fall (in the mornings) and, even more important, for cooling on summer evenings. Benjamin Franklin was right about candles, in other words, but he did not consider air-conditioners.”

They point out that, “In regions of the United States where demand for air-conditioning is greater than in Indiana, this spike in cooling costs is likely to be even greater.”

Their article was based on a paper they have written for the National Bureau for Economic Research.


So if DST increases heart attack incidence, increases car accidents, and costs us more in energy consumed, why do we do this?  There doesn’t seem to be a good reason, it’s just something we tried and turns out doesn’t work.   Franklin’s candle wax calculation were written half in jest, not so much as a practical suggestion, but more as a critique of life in Paris where the well off rarely got out of bed before noon.  It may prove to unmake this tradition or perhaps the energy saving that could result from repealing the DST laws may make it a no-brainer.

In the meantime, come April, it would make sense to address the increased health risks associated to changing to DST, at least with our high risk patients.  The easiest fix would be to make the change gradually, for example, changing the alarm at daily ten-minute increments for a week rather than the full hour on one day.  I plan to tell our front desk to start my patient appointments later for a few days.    


Ben Franklin’s letter:

2004. Journal of the American College of Cardiology published and article on the ‘Effect of sleep loss on C-reactive protein, an inflammatory marker of cardiovascular risk.’

Jansky’s article in NEJM:

Kotchen and Grant on DST in Indiana paper:


Franklin, Ben. Letter to the Editor of the Journal of Paris, 1784


Curr Biol. 2007 Nov 20;17(22):1996-2000. Epub 2007 Oct 25.    

    The human circadian clock's seasonal adjustment is disrupted by daylight saving time.

    Kantermann T, Juda M, Merrow M, Roenneberg T.

    Ludwig-Maximilian-University, Goethestrasse 31, D-80336 Munich, Germany.

    A quarter of the world's population is subjected to a 1 hr time change twice a year (daylight saving time, DST). This reflects a change in social clocks, not environmental ones (e.g., dawn). The impact of DST is poorly understood. Circadian clocks use daylight to synchronize (entrain) to the organism's environment. Entrainment is so exact that humans adjust to the east-west progression of dawn within a given time zone. In a large survey (n = 55,000), we show that the timing of sleep on free days follows the seasonal progression of dawn under standard time, but not under DST. In a second study, we analyzed the timing of sleep and activity for 8 weeks around each DST transition in 50 subjects who were chronotyped (analyzed for their individual phase of entrainment). Both parameters readily adjust to the release from DST in autumn but the timing of activity does not adjust to the DST imposition in spring, especially in late chronotypes. Our data indicate that the human circadian system does not adjust to DST and that its seasonal adaptation to the changing photoperiods is disrupted by the introduction of summer time. This disruption may extend to other aspects of seasonal biology in humans.


Eur J Epidemiol. 2005;20(5):395-9.

Excess cardiac mortality on Monday: the importance of gender, age and hospitalisation.

    Witte DR, Grobbee DE, Bots ML, Hoes AW.

    Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, The Netherlands.

    BACKGROUND: Available evidence suggests a peak in the incidence of cardiovascular events on Mondays compared to other days of the week. The underlying mechanism may be summarised as naturally occurring rhythmic fluctuations in human physiology, and socially determined rhythms in human behaviour. Change in these rhythms may lead to attenuation of the peak on Mondays. OBJECTIVE: To quantify the excess risk associated with the Monday peak in cardiovascular mortality and to explore the role of age, gender and hospitalisation. METHODS: Details on time and cause of all deaths which occurred in the city of Rotterdam between November 21, 1988 and November 21, 1990 were obtained by sending a questionnaire to the physician who signed the death certificate. We studied the weekly distribution of 1828 confirmed cases of sudden cardiac death, for the group as a whole and in subgroups according to gender, age (< 65 years/65 years) and hospitalisation. RESULTS: The odds ratio (OR) of sudden cardiac death on Monday compared to other days of the week was 1.20 (95% CI: 1.06-1.36). The excess mortality due to the Monday peak amounted to 4.9 per 1000 deaths. The Monday peak was more pronounced in non-hospitalised (OR: 1.25; 95% CI: 1.08-1.44) than in hospitalised patients (OR: 1.06; 95% CI: 0.83-1.37), in men (OR: 1.25; 95% CI: 1.06-1.48) than in women (OR: 1.14; 95% CI: 0.95-1.36), and in those younger than 65 (OR: 1.29; 95% CI: 0.95-1.74) compared to those aged 65 years or over (OR: 1.18; 95% CI: 1.03-1.35). Yet, the confidence limits overlap. CONCLUSION: The incidence of sudden cardiac death is markedly increased on Monday, more pronounced in non-hospitalised patients. Our results may point to the relevance of naturally occurring rhythmic fluctuations in human physiology, and socially determined rhythms in human behaviour as underlying mechanism.

Imre Janszky,. Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. NEJM. Vol. 359:1966-1968, Oct 30, 2008, Num 18.

Sleep Med. 2001 Jan;2(1):31-36.    

    Fatal accidents following changes in daylight savings time: the American experience.

    Varughese J, Allen RP.

    Department of Symbolic Systems, School of Humanities and Sciences, Stanford University, CA, Stanford, USA

    Objective: This study examines specific hypotheses that both sleep loss and behavioral changes occurring with the time shifts for Daylight Savings Time (DST) significantly effect the number of fatal traffic accidents in the United States of America. Background: It has been reported that there is a significant increase in the number of automobile accidents in the spring shift to DST due to the loss of 1 h of sleep. But the extra hour gained at night with the shift from DST in the fall has been variably reported to be associated with increases and decreases in the number of automobile accidents which may reflect either behavioral anticipation with an extended late night prior to the change or the benefit of extra sleep after the change. Methods: Data from 21 years of United States' fatal automobile accidents were gathered. The mean number of accidents on the days at the time of the shifts (Saturday, Sunday and Monday) was compared to the average of the corresponding mean number of accidents on the matching day of the weeks preceding and following the shift. This was repeated for each DST shift. The number of accidents for a particular shift was also correlated with the year of the accidents. Results: There was a significant increase in accidents for the Monday immediately following the spring shift to DST (t=1.92, P=0.034). There was also a significant increase in number of accidents on the Sunday of the fall shift from DST (P<0.002). No significant changes were observed for the other days. A significant negative correlation with the year was found between the number of accidents on the Saturdays and Sundays but not Mondays. Conclusions: The sleep deprivation on the Monday following shift to DST in the spring results in a small increase in fatal accidents. The behavioral adaptation anticipating the longer day on Sunday of the shift from DST in the fall leads to an increased number of accidents suggesting an increase in late night (early Sunday morning) driving when traffic related fatalities are high possibly related to alcohol consumption and driving while sleepy. Public health educators should probably consider issuing warnings both about the effects of sleep loss in the spring shift and possible behaviors such as staying out later, particularly when consuming alcohol in the fall shift. Sleep clinicians should be aware that health consequences from forced changes in the circadian patterns resulting from DST come not only from physiological adjustments but also from behavioral responses to forced circadian changes.


New York Times

November 20, 2008

Op-Ed Contributor

What’s the Point of Daylight Time?