Talk:Daylight saving time

Health effects of Spring circadian rhythm disruption

Health effects of Spring circadian rhythm disruption

The enforced sleep deprivation and circadian rhythm disruption of the Spring time change has a number of adverse health effects. PMID 11152980. The body's circadian rhythm does not readily adjust to the effects of the Spring change; instead, the body continues to slowly adjust to the earlier morning sunlight. PMID 17964164. The circadian rhythm does more readily adjust to the Fall change, which allows an hour of extra sleep PMID 17964164; for instance; an actual reduction of traffic fatalities has been seen following the Fall change. PMID 7832269. Because the Spring change imposes a number of ill health effects, the nation of Kazakhstan discontinued the use of Daylight saving time.

Given the dissaprate effects, it is difficult to understand why there is no delay in the Spring change. The clocks change at about the spring equinox in Europe and the United States, but well over a month after the autumnal equinox.

The opposite would make sense for purposes of health. The body's circadian rhythm readily adjusts to the Fall change, which allows more sleep, but adjusts with great difficulty and slowness to the Spring change, which effective deprives an hour of sleep (measured at just over 60 minutes in one study) and requires rising earlier. After the change, people continued to rise earlier on the weekends in a pattern precisely tuned to the gradually earlier rising of the sun. For health reasons, the Spring change should be delayed for at some weeks after the Spring equinox, to allow the body has the chance to adjust based on sunlight. Possibly a part of the reason that the body adjusts so easily is the Fall is simply that the natural light progression has already occurred in the month following the equinox. See notes in the discussion section above on health effects of circadian rhythm disruption.

---

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. Abstract

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.

PMID: 17964164

---

Am J Public Health. 1995 Jan;85(1):92-5. Daylight saving time and motor vehicle crashes: the reduction in pedestrian and vehicle occupant fatalities.

Ferguson SA, Preusser DF, Lund AK, Zador PL, Ulmer RG.

Insurance Institute for Highway Safety, Arlington, Va 22201. Abstract

Fatal crashes were tabulated for 6-hour periods around sunrise and sunset, from 13 weeks before the fall change to standard time until 9 weeks after the spring change to daylight saving time. Fatal-crash occurrence was related to changes in daylight, whether these changes occurred abruptly with the fall and spring time changes or gradually with the changing seasons of the year. During daylight saving time, which shifts an hour of daylight to the busier evening traffic hours, there were fewer fatal crashes. An estimated 901 fewer fatal crashes (727 involving pedestrians, 174 involving vehicle occupants) might have occurred if daylight saving time had been retained year-round from 1987 through 1991.

PMID: 7832269 [PubMed - indexed for MEDLINE]PMCID: PMC1615292Free PMC Article

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 Abstract

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.

PMID 11152980

See also

General topic

• Daylight saving time around the world
• Time in Canada
• CHU distributes official time in Canada

Official Civil Time Distribution

• WWV & WWVH (NIST Shortwave)
• WWVB (NIST Longwave)

Quasi-governmental time distribution systems

• CDMA cellphone stratum 2 time distribution system
• GNSS global navigation stratum 1 time distribution system

Farmers

"Conversely, DST can adversely affect farmers and others whose hours are set by the sun.[4] For example, grain harvesting is best done after dew evaporates, so when field hands arrive and leave earlier in summer their labor is less valuable." But DST is not in effect in the summer, so how can less efficient use of labor in the summer be a adverse effect of DST?! GeneCallahan (talk) 19:59, 28 October 2011 (UTC)

Where I live DST is only used in summer, and I thought that was the case everywhere (apart from places where it lasts all year). The lead is pretty clearly about DST being in summer time. Where are you? HiLo48 (talk) 22:52, 28 October 2011 (UTC)

I don't think it's much of a problem to change farm hands' working hours during summer accordingly? -- megA (talk) 14:33, 30 October 2011 (UTC)

Leaving aside the misunderstanding above, it leads me to question the sentence for other reasons. We mention several times in the article that farmers are generally opposed to DST. However, the references we use seem to be primarily referring to arguments made almost a hundred years ago, and the latest seems to be from the 1950s. Surely we should get some more up-to-date information regarding the feelings of the agricultural sector? Most of the arguments from the older times regarding milk trains and the working hours of farm hands are surely of relatively minor concern in the modern world of industrial agriculture? Does anyone know of any real arguments from the modern agricultural sector regarding DST? Peregrine981 (talk) 14:07, 4 January 2012 (UTC)

compounding problems of standard time

"DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies.[121] Also, sun-exposure guidelines like avoiding the sun within two hours of noon become less accurate when DST is in effect.[122]"

Surely this is a very trivial concern that we needn't clutter the article with? MAYBE I can agree to the sundial concern, although this seems a bit trivial considering the many other potential problems with sundials, but the notion that sun exposure guidelines are less effective seems fairly ludicrous, even if it technically correct. Peregrine981 (talk) 15:34, 5 January 2012 (UTC)

"temporarily advancing the clocks"

In the intro, it says that in DST the clocks are "temporarily" advanced forward. Well... if March-til-October counts as "temporarily", then ok. But, to my understanding, the better part of the year - i.e. seven months - is a somewhat longer period than is covered by the notion of "temporary" - however philosophically one might wish to view it. In fact, the astronomically correct non-DST time is much more "temporary" than DST! my two cents :-) BigSteve (talk) 09:47, 1 February 2012 (UTC)

Microsoft

Am I the only one who thinks the section under Microsoft has become too large, verging on trivia? The text that was included when this article passed through FAC seems to me a better overall balance. Thoughts? Eusebeus (talk) 10:31, 16 February 2012 (UTC)

The last paragraph is trivia. Tellingly, it begins with "An interesting effect..." The other main difference is the third paragraph, not sure exactly how useful that one is. CMD (talk) 13:44, 16 February 2012 (UTC)