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The Great East Japan Earthquake

Daylight Saving Time and Biological Clocks: To Get Through Summer Power Conservation

Shigenobu Shibata
Professor, Faculty of Science and Engineering, Waseda University


Conserving electricity is an absolute necessity due to the power shortage associated with the Great East Japan Earthquake Disaster. Electricity consumption increases in proportion to human social activities. One problem in particular is the large difference between the maximum and minimum electricity consumptions during a day (the solid lines in Figure 1A). The daily rhythm of electricity consumption is formed by social activities conducted according to the biological clocks inside living bodies. Currently, there is a movement toward efforts for less electricity consumption through the introduction of daylight saving time in summer, where the clock is set forward by one hour. In this essay, we examine whether daylight saving time is really effective for conserving power, and whether it may burden biological clocks.

Circadian rhythm controls rhythm in around one day

Circadian rhythms are rhythms on about a 24-hour cycle, such as the rhythms of body temperature, blood pressure, and the sleep-wake rhythm. Because the behavior of clock genes is well known related to this rhythm, the term of biological clocks practically means clocks that activate this rhythm. The cycle of biological clocks controlling the circadian rhythms of humans is about 24.5 hours. It is not just 24-hours so that humans can respond to variations in the length of the day (seasonal variations). The cycle 0.5 hours longer than the 24-hour rotation period of the earth means that the morning sun pushes our biological clock forward by 0.5 hours every day. Repeated stimuli synchronizing circadian rhythms to generate daily rhythms are called entraining agents. Light-dark cycles, feeding cycles, and temperature cycles are known as some of the important entraining agents.

Photic entrainment and biological clocks

It has been found that morning light at wakeup time is important in the advancement of human biological clocks, and that they may be delayed by exposure to strong light at night in convenience stores or other places. If you are exposed to strong light at night and sleep past the time in the morning when your biological clock is supposed to be advanced during a weekend from Friday through Saturday and Sunday, your biological clock is delayed day by day. If you awake at the normal time on Monday after the weekend, you may show symptoms called Blue Monday. In general, the effect of light synchronizing biological clocks is proportional to the product of the length of light irradiation time and the strength of the light.

Biological clocks are distributed around your body

It can easily be anticipated that circadian rhythms are generated by many clock genes expressed at the suprachiasmatic nucleus (SCN), where the master clock exists. Studies revealed, however, that the rhythms are also tapped out at the cerebral cortex and the hippocampus in the brain, the heart, the lungs, the liver, the kidneys, the skin, and others. The dotted lines in Figure 1A indicate daily rhythms with clock genes Per 2. In a hierarchical system compared to an orchestra, SCN is the conductor (the master clock), and the musical instruments are represented by clocks located in the peripheral organs including the cerebral cortex and the hippocampus in the brain (brain clocks), the liver, and the heart (peripheral clocks). SCN instructs the timing of play to make a harmonious orchestra.

Feeding entrainment and biological clocks

Recent studies have found that keeping a regular dietary pattern plays an important role in phase resetting of biological clocks. It has also been revealed that rhythm in the liver is easily synchronized with a meal after a long period of fasting-i.e., breakfast-and easily digestible starchy materials are good for it. Because feeding entrainment occurs at peripheral clocks and clocks in the brain excluding ones at SCN, it is also a method useful for remedying rhythm irregularity such as jet lag.

Daylight saving time and staggered working hours

Daylight saving time is a system employing a time zone where one hour is added to the current hours, or simply an additional hour, for the purpose of efficiently using hours when the sun is in the sky in summer to work while it is still light out and extend night leisure time. This scheme is widely used in European countries with high latitude and long sunlight hours in summer. By the way, there is a similar idea called staggered working hours for effectively using summer morning hours. Let me explain the difference between them. Suppose that a company starts work from nine o'clock. Moving this start time to eight o'clock constitutes staggered working hours. Whereas the start time remains nine o'clock under a daylight saving time scheme, on the other hand, the time by which employees need to arrive at the company corresponds to eight o'clock before introduction of daylight saving time. Under both schemes, the time to come into office is shifted from nine to eight o'clock. So, employees have to get up at least one hour earlier in the morning.

Therefore, it is wrong to say that a company introduced daylight saving time for saving electricity this summer. Instead, a correct expression is that they introduced staggered working hours. In factories, personnel frequently go to work earlier or later as a usual practice. A staggered working hour scheme introduces this practice into white-collar work as something like in-house daylight saving time.

So, why is the government unwilling to introduce daylight saving time to efficiently use morning hours? The answer is that it would not lead to lower consumption of electricity. Instead, longer evening hours might encourage more electricity consumption through use in leisure time. A current problem is how to decrease the maximum electricity use during the daytime. As shown in Figure 1B, therefore, the introduction of daylight saving time may only shift the peak time of electricity consumption forward. The peak might, furthermore, even last longer in some cases.

Staggered working hours and shift work

There is another working arrangement called shift work, by the way, where employees rotate day, twilight, and night shifts. Because the peak hour of individual activities slides gradually in this arrangement, electricity consumption has no projections in terms of weekly consumption. What is the difference between earlier, later, and night work and day, twilight, and night shifts? The rhythm is fixed in the former, while the phase of the rhythm slides continuously in the latter.

Shift work may cause abnormality in biological clocks, increase the risk of obesity and diabetes, and cause or increase cancer. In particular, it is pointed out that it may enhance risk of breast, prostate, and colon cancer. It may also cause risk of insomnia, depression, and other mental diseases. Accordingly, night work with fixed rhythm imposes less of the burden on biological clocks than shift work.

A proposal for a lower peak of electricity consumption based on biological clocks

According to findings from studies on sleep, humans can be broadly categorized into morning, intermediate, and night persons. Morning persons should move their life rhythm forward by one or two hours to adopt earlier work, intermediate persons should remain as they are, and night persons should shift their life rhythm backward by one or two hours to do later work, attempting to level off the peak (Figure 1C). In other words, daylight saving time should never be introduced to move the entire social life earlier. Earlier or later work may be used depending on business categories. For example, elementary and junior high schools might adopt earlier work, while high schools and universities may rely on later work.

Figure 1: Daily rhythm of electricity consumption (A, solid line) and rhythm of clock gene Per 2 expression (A, dotted line). Cases of a peak phase moved forward by daylight saving time (B, dotted line), and a peak leveled off by earlier and later work (C, dotted line).

Shigenobu Shibata
Professor, Faculty of Science and Engineering, Waseda University

Professor Shibata graduated from the School of Pharmaceutical Sciences, Kyushu University in 1976. He withdrew from the doctoral program, Graduate School, Division of Pharmaceutical Science, Kyushu University, after completing the course work in 1981. After assuming positions of Research Associate, Associate Professor of pharmaceutical science, and others in the School of Pharmaceutical Sciences in Kyushu University, he became an Associate Professor in 1995 and a Professor in 1996 on the School of Human Sciences, Waseda University. He became a Professor, Department of Electrical Engineering and Bioscience, School of Science and Engineering, Waseda University in 2003, and a Professor, Department of Electrical Engineering and Bioscience, School of Advanced Science and Engineering, Waseda University in 2006. He has been a Visiting Professor at Tokyo University of Agriculture and Technology since April 2009, and a Visiting Professor at Tokyo Women's Medical University since June 2011. Professor Shibata was awarded The Pharmaceutical Society of Japan Award for Young Scientists in 1994. He has also been a board member of the Japanese Society for Chronobiology since 2004, and a Vice Chair of World Federation of Societies for Chronobiology since 2001.

[Major Publications]

"Importance of Breakfast from the Perspective of Chrononutrition [Jikan-eiyogaku kara Kangaeru Choshoku no Juyosei]," Lactobacillus News [Nyusankin Nyusu], Spring 2011 "Change your Dietary Life with Chrononutrition [Jikan-eiyogaku de Shokuseikatsu wo Chenji]," Healthy Family [Sukoyaka Famiri], May 2011 "How to Utilize Morning [Asa no Katusyo-ho]," Nikkan Health Premie [Nikkan Herusu Purumie], February 2011, and more.

Books and Review Articles
Shigenobu Shibata, "Biological Clocks and Metabolism [Tainai-dokei to Taisha]," Journal of Chronobiology [Jikan-seibutsugaku], Kagakudojin, 2011 Shigenobu Shibata, "Effects of Foods on Biological Clocks [Shokuhin no Tainai-dokei ni taisuru Eikyo]," Chronobiology & Industrial Applications [Tainai-dokei no Kagaku to Sangyo Oyo], CMC Publishing, 2011 Akiko Hirao and Shigenobu Shibata, "Effects of Biological Clocks on Nutrition and Food Ingestion [Tainai-dokei ga Eiyo Shokumotsu Sesshu ni Oyobosu Eikyo]," in Chronobiology & Industrial Applications [Tainai-dokei no Kagaku to Sangyo Oyo], CMC Publishing, 2011, and more.

Introduction to his lab:http://www.eb.waseda.ac.jp/top/applicants/laboratory/12shibata.html