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Our Biological Clocks’ Battle against Real Clocks

Isabella Bautista | January 25, 2023
Pictured here are Lisa Monteggia, Ph.D.; Carl Johnson, Ph.D.; Beth Malow, M.D.; and Douglas McMahon, Ph.D. Graphic by Helen Qian.

The phrase “fall backward, spring forward” likely reminds you of daylight saving time (DST), the convention most of us are grateful for in November but dread in March when we lose an hour of sleep. DST originated during World War II, when then-President Franklin D. Roosevelt instituted the concept to try to save electricity that would normally be used for lights. 2022 marked the eightieth anniversary of the implementation of DST. With 80 years of DST behind us, it’s time to ask the question: is the extended time in the sun worth the hit to our bodies’ circadian rhythms, or is it time to eliminate DST once and for all?

On October 26, the Vanderbilt School of Medicine hosted a webinar called “The Science of Circadian Rhythms and Daylight Saving Time.” The webinar centered around a panel of Ph.D. faculty members: Douglas McMahon, Beth Malow, Lisa Monteggia, and Carl Johnson. Each member of the panel took turns presenting objective information about the relationship between DST and circadian rhythms in addition to their professional opinions on the matter. For example, McMahon shared how his research on mice and honeybees shows how light, specifically seasonal light, can affect mental health. Malow described his experience testifying on DST before Congress, and Johnson shared about how he has been studying biological rhythms since his undergraduate years.

Each of us has a daily routine. Under ideal circumstances, we rise and sleep around the same time each day, and we get hungry around the times we usually eat breakfast, lunch, and dinner. We feel awake in the morning and become progressively more tired, especially throughout the evening, until we go to bed. According to the panel in the webinar, this daily timing is not just based on our environment—it is rooted within us in a sort of biological clock known as our circadian rhythm. Even if you place humans in an environment where they have no way of telling what time it is, they will continue to follow the timing of our biological clock.

Challenges to Our Circadian Rhythms

Our circadian rhythms are the happiest when environmental factors do not inhibit their ability to function. However, we often don’t function under “ideal conditions.” 

One thing that negatively impacts our circadian rhythm is jet lag caused by differences in time zones between different locations on a trip. Most humans can easily compensate for one-to-two-hour jet lag within a day, but anything more than that throws off our biological clocks. The only thing we can do to ameliorate the effects of jet lag is try to adjust to the new time zone gradually before flying there. However, Malow says this is quite difficult. In her personal experience, she has done well adjusting when going to a time zone ahead of Nashville’s, but she has trouble adapting when she returns home. Although there is some individual variability, she says that morning people usually are in the same situation as her as far as jet lag adjustment goes, and night owls are the opposite. For this reason, sports teams with a lot of night-owl players are at a disadvantage if they have to fly east for their sporting event.

Shift workers have a similar problem with their circadian rhythms. Unpredictable, fluctuating work schedules make it difficult to maintain a regular sleep schedule. According to the panel, there is “nothing good about shift work, circadian rhythm-wise.” Irregular sleep schedules cause hormone levels to go completely awry, which can activate genes that contribute to cancer, diabetes, obesity, heart disease, and more. To mitigate the effects of shift work, people should maximize light exposure during their shifts and minimize it off shift to mimic a normal light-dark cycle as best as possible. 

Light: The Biggest Factor

As suggested above, light is in fact the strongest stimulus for our circadian rhythms. This fact is why DST affects our routines so strongly: DST does not change the light available when we wake up because we cannot control the sun and the movement of Earth through space, but it does change the time. This creates a disconnect between what our bodies think the time should be based on light exposure and what the time actually is. This circadian misalignment leads to hormone inconsistencies, such as those experienced by shift workers. For example, levels of the sleep-inducing hormone melatonin and the stress-regulating hormone cortisol can be off, resulting in irregular sleep patterns and anxiety levels.

According to national polls, the majority of Americans want to stop participating in DST. In March 2022, the U.S. Senate voted to end DST, starting in November 2023. Mexico has decided to do so as well. 

In addition to its negative effects on our circadian rhythms, DST has also not been shown to serve its intended purpose—it saves little to no energy. Put together, these are more than sufficient reasons to advocate against DST. Hopefully, with the return to standard time, we (and our circadian rhythms) will be much happier.


Schmiedeberg, R. (2022, October 31). Why Do We Still Have Daylight Saving Time in California? NBC San Diego. Retrieved November 16, 2022, from

Vanderbilt University. (2022, October 26). Circadian Rhythms.