xxxvii. Daylight Saving Time / Summer Time

27 October 2007 at 13:33 | Posted in Circadian rhythm | Leave a comment
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In 2005, Kazakhstan stopped using Summer Time (Daylight Saving Time, DST). Dr. Zaira Majitova, MD, said: “A human body has its own biological watch which runs synchronously with nature’s watch. When the human body is forced to readjust artificially, it leads to disturbances in the biological watch.” Doctors reported a long list of health complications resulting from the hour lost in the springtime.

In 2006, Finnish researchers at their National Public Health Institute published their study showing that the transition to daylight saving time reduces sleep duration by over an hour and reduces sleep efficiency by an average of 10%.

Now in 2007, scientists in Germany and Switzerland report: The Human Circadian Clock’s Seasonal Adjustment Is Disrupted by Daylight Saving Time. Two studies are here rolled into one.  First, data from a large survey which examined sleep patterns of 55 000 people in Central Europe were mined. Under standard time, sleep timing on free — usually weekend — days follows the seasonal progression of dawn. Under summer time, it does not.

In the second study, they analyzed the timing of sleep and activity for eight weeks around each of the two annual transitions in 50 people, taking into account each individual’s natural chronotype, ranging from morning larks to night owls. They found that the timing of both sleep and peak activity levels readily adjust to the release from DST in autumn, but that the timing of activity does not adjust to the start of DST in spring. In everyone, but especially in the night owl chronotypes, biological timing stays on standard (winter) time, while our social schedules must be adjusted to the advanced clock time throughout the summer. “When we implement small changes into a biological system which by themselves seem trivial, their effects, when viewed in a broader context, may have a much larger impact than we had thought,” says Till Roenneberg of Ludwig-Maximilian-University in Munich.

Both sleep times and daily activity patterns were tracked. The time of mid-sleep in the large population correlates with dawn under standard time but is widely scattered under DST. In the smaller study, daily activity patterns most clearly show the lack of adjustment to DST; sleep times show the same thing but to a lesser degree.

From the study report: “the human circadian clock tracks dawn under standard time but not under DST. Whereas the human clock … predictably advances from autumn to spring …, it remains locked to the same time between spring and autumn…. These results, in combination with those from the database, suggest that the incomplete adjustment of activity in larks and the nonadjustment in owls continues … throughout the months of DST.”

“Like other animals, humans are seasonal (in birth rates, mortality, suicide rates, etc.). However, seasonality in humans has drastically declined in industrialized countries over the last 60 years. The main reason for this is probably increased shielding from [nature], but DST might constitute an additional factor for the dissociation of human biology from the seasons.” I do so agree. Our circadian rhythms are primarily connected to dawn, not to sundown. A Wikipedia illustration shows very clearly how our exposure to the natural dawn cycle is changed by our use of daylight “saving” time.

Figure 4, “Relationship between Natural and Behavioral Light-Dark Cycles with and without DST” in the 2007 report linked to above, shows and explains the same thing. There, the “enforced delay of seasonal progression” is shown, and it’s pointed out that the “amplitude of the relationships as well as the degree of their perturbations by DST increase with latitude.”

A quarter of the world’s population is subjected to the one-hour time change twice a year, and the impact is still not understood. I’ve never liked DST, but I’ll let Coturnix say it for me: “In this day and age of around-the-clock life, global communications, telecommuting, etc., the clock-shifting twice a year has outlived its usefulness and should go the way of the dodo.”

I’m writing this blog post at exactly the wrong time of year, of course. All studies show that in the autumn, everyone fully adjusts to standard time within a week. It’s the transition in spring which causes problems.


Next:  xxxviii. Eveningness vs. DSPS



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