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  • Writer's pictureWellFit by Jennie

Daylight Saving Time and Circadian Rhythm

Updated: Mar 5



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Daylight Saving Time: What and When is it?


Twice a year, most U.S. states and around 70 other countries change their clocks. In 2023 in the U.S., we will “spring forward” on Sunday, March 12 by turning our clocks forward by one hour and will “fall back” on Sunday, November 5 by turning our clocks back by one hour.



Daylight Saving Time (DST) as an idea has been around for a very long time. There is evidence that ancient civilizations used a system comparable to the one we use today. Two New Zealand scientists presented this idea in 1895, but it would be the early 20th century before it its modern-day implementation in the U.S. and elsewhere.


Why Does DST Exist in the First Place, and Who Does it really Help?


Why would we follow this practice? Due to the 23.4-degree angle of the Earth’s tilt, the northern hemisphere enjoys an increase in daylight hours during the late spring, summer, and early fall. DST shifts these daylight hours to later in the day, providing an extra hour of daylight after a typical 9-5 work shift. This has been thought to conserve energy with people having less time using electricity inside to light their homes. It also delays the morning sunrise by an hour.



Who benefits from DST? In the U.S., the Chamber of Commerce has been in support of DST to help the retail industry, including both small businesses and big box stores. Workers presumably have more time after the workday to engage in sporting and recreational pursuits, and spend at various shops and malls. There are also proponents of DST claiming a reduction in crime with more daylight in the evenings.


DST has incorrectly been attributed to the farming industry, who has actually taken a stance against its implementation.


Negative Consequences of Twice-a-Year Time Change


Most anyone on any type of schedule can recognize the potential havoc this twice-a-year time change wreaks. “Spring forward” has widespread negative consequences that is reflected in the recent proliferation of news and media. At best, “losing an hour” causes grogginess, brain fog, and presenteeism at work on the following Monday and into the work week. Adjustment to DST can take up to a full week. At worst, the implications of the switch to DST for health and safety are far more serious.



Consider the following facts:

- Heart attacks increase by an average of 24% on the Monday after the DST switch.

- The overall rate of ischemic stroke is 8% higher during the first two days after DST.

- There is a 6% spike in fatal car accidents the week following DST, resulting in 28 additional deaths per year

- Compared with other days, more workplace injuries and injuries of greater severity happened on the Monday after DST went into effect.



Where Does the Law Stand on this Issue?


In the U.S., Daylight Saving Time (DST) was extended from 30 to 34 weeks starting in 2007. The then-President signed a law to have it begin three weeks earlier on the second Sunday in March and end one week later the first Sunday in November.


In March 2022, lawmakers in Virginia advanced a proposal to keep the Sunshine Protection Act (DST) in effect year-round to avoid the hassle and cost of changing our clocks twice each year. This can only be implemented, however, if Congress enacts a law allowing the states to do so.



At the moment, the issue is stalled in the House of Representatives with its fate remaining to be seen. Some lawmakers just want to stop changing the clocks; others want more daylight later in the day year-round; and yet others, heeding the science around this issue, desire a permanent change to standard time. This isn’t the first time that some governmental officials have conveniently overlooked or ignored the science around this or other topics that affect our health.


Let’s Consider the Science on DST vs Standard Time as it Relates to Our Health


Circadian rhythms govern all our bodily systems. These 24-hour rhythms heavily influence our physical, mental, and behavioral functioning. There is literally a clock for just about every body function you can imagine.



The best known of these rhythms involve our sleep/wake cycle. With this diurnal rhythm, we produce cortisol during daylight hours and melatonin when it is dark outside. Cortisol and melatonin run in opposition to each other; that is, we are producing either one or the other of these hormones at a given time, but not both. When we encounter bright light, this light hits the melanopsin cells in the retina of the eyes and signals to the brain via the suprachiasmic nuclei (master clock) to the pineal gland that it is time to be awake and thus the body responds by producing cortisol for alertness. Thus, the melatonin “spigot” is turned off.


Likewise, as it becomes dark outside, we produce melatonin to prepare us for sleep. Now the cortisol “spigot” is turned off. Interestingly, melatonin also has anti-cancer properties.

Our daylong biological clock is actually set to about 24.3 hours, but each morning, daylight pulls us back into the 24-hour cycle in standard time.


During standard time, 12PM is referred to as “solar noon”, the clock time in which the sun is highest in the sky. Our bodies evolved to work in sync with this timing. Thus, when we are in standard time, we are synchronized with the rhythms of nature and our planet, and better regulated physiologically, all of which is compatible with good health. Bright light early in the day helps to regulate mood, metabolism, cardiovascular function, and performance, and can affect appetite, physical activity and cognition.



When we “spring forward” to DST, we experience everything that comes along with losing an hour of sleep, which is more dysregulating than one would think. All the above-noted consequences of this can and do occur as a result. At best, we experience “social jet lag” in which our body clock, wanting its usual bed and wake time, causes us to feel groggier and less functional on the days after this change. During DST, our wall clocks read 11AM when it is actually solar noon.



When we “fall back” to standard time, we generally do not have negative consequences and are merely enabled to fall back into our natural rhythm. Greater physiological regulation comes with better health as the body systems are brought back into natural alignment once again.


Staying in DST year-round would put us in a state of chronic circadian misalignment. We would essentially be dismissing the earth’s solar clock, from whence our internal body clock follows, in favor of a contrived, man-made time we arbitrarily decide to set on our wall clocks.


In the summer, we have longer periods of daylight throughout the day. Consequently, the sunrise occurs sufficiently early to help our bodies adjust and regulate.


However, starting in the fall, daylight hours are shorter. Keeping DST year-round means that people are more likely to have to get up well before sunrise in the fall and winter. Year-round, darkness falls later, which doesn’t give our brains a timely, natural signal to start winding down in preparation for bedtime.


This Washington Post article gives a very clear, animated description on the effects of DST versus standard time:


The following groups, in addition to countless doctors and scientists, are not in favor of year-round DST, and instead support a switch to year-round standard time:


Dr. Chris Winter, a Charlottesville, VA neurologist and sleep specialist, addresses the DST issue in his podcast entitled Sleep Unplugged: Daylight Saving Time: What Exactly Are We Saving?


What Action Can You Take?


For information on how you can support a move to year-round standard time, this website is a great resource: Save Standard Time



In the meantime, unless you live in Hawaii or Arizona, start preparing for the shift to DST by winding down and going to bed, and getting up in the morning, incrementally earlier the week or two before the time change. Wake time has a greater effect on setting circadian rhythm than does bedtime, along with getting bright light and movement earlier in the day. Have a good eye mask handy and avoid bright light and backlit devices for the hour or two before bed.


There are many examples in which we as humans tend to go against our essential nature. As living beings on this planet, we need to remember that we are nature. We are subject to the laws of nature and thus the laws of health. It is worth the effort to educate ourselves and base our decisions on essential scientific truths on matters involving our health!




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