Jim Wilson/The New York Times

November 9, 2023

How The Body’s Circadian Rhythms React To Daylight Savings, Cornell Prof Explains 

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As of Nov. 5, daylight saving time — the period when clocks shift forward in early March, originally intended to conserve energy by providing more daylight and eliminating the necessity for excess artificial light — has come to an end, and the clocks have shifted an hour backwards to standard time. Though much of the mainstream media, particularly policy makers, debate the usefulness of this time change, the arguments on either side can be clarified by its biological impacts on humans — something traced back to circadian rhythms.

The transition back to standard time — the time zone utilized during winter and early spring — is argued to have larger health implications. Some scholars speculate that this time shift may correlate with seasonal depression, cardiovascular impairments/heart attacks, car crashes and potential stroke

Many agree that lethargy follows time switches and earlier darkness, according to the American Academy of Sleep Medicine, which noted that 55 percent of individuals admit to feeling tired after the transition. These associated effects are linked to circadian rhythms, the body’s internal biological clock responsible for the behavioral, physiological and molecular changes that can happen over the course of 24 hours. 

According to Prof. Brian Crane, chemistry and chemical biology, circadian rhythms are a “highly conserved timing device” that pertains to the “molecules inside the cells [that] basically create an oscillator that oscillates within about a 24 hour period.” This internal clock functions relative to environmental stimuli, impacting the sleep-wake cycle as well as eating patterns, digestion, body temperature, hormones and other bodily mechanisms. 

The circadian rhythm system works molecularly via protein synthesis. According to Crane, around five to 10 percent of genes expressed in a human organ will be under circadian control.

These genes encode for proteins that regulate the circadian system. 

This regulation is important because protein cycles oscillate throughout the day relative to one’s surroundings, particularly light stimuli. In other words, the sleep-wake cycle is set by the amount of light coming into the nervous system, which is why we get more tired when it is dark.

Crane explained that, despite the fact that scholars are not sure how light stimuli changes protein synthesis molecularly, circadian rhythms understand that light, the largest repetitive stimuli on the planet, is a major factor that creates the 24-hour cycle. “Although we don’t really understand how this happens, we know that when they’re exposed to light, it causes them to do this transcriptional activation,” Crane said. 

This then leads into the impact of a time change, as altering the clocks also transforms the body’s access to light, thereby impacting its molecular-biological oscillations. In the case of returning to standard time, this circadian rhythm is how our body adapts.

When the environmental stimuli, specifically light, is out of sync with the previously normal patterns of the circadian feedback loop, it takes one to two days for these mechanisms to shift back and for the body to properly coordinate, Crane explained. This adaptation is considered a ‘reset’ which can occur at different times in relation to specific body parts.

“It turns out that the ‘clocks’ in your eyes and your brain, which are the ‘master clocks’ closest to light stimuli, are reset pretty quickly,” Crane said. The rest of the body, however, does not adjust as fast, causing potential sluggishness. This one hour difference can cause an almost jet-lagged feeling when portions of the stomach, intestine and liver are out of sync with the eyes, brain and external environmental timing.

For undergraduate students in particular, this slight misalignment may not be of such grave concern. Crane noted the term “social jetlag,” which occurs when young individuals alter their sleep schedules on the weekends. Despite having some indications of decreased productivity and creativity, such behavior provides evidence for the ability to adapt to various times and sleep schedules in the young generation. 

“Young people are very robust, so [they’re] probably not doing huge damage,” Crane said. 

Most importantly for young people, sleep schedules are the main factor being influenced by circadian rhythms and the standard time. Many scholars find that this annual November transition away from daylight savings time decreases sleep disruptions, not only from the one hour of sleep gained, but also more generally. 

According to Crane, several studies suggest individuals who get more light in the early morning can “sleep more with less interruption” and need less sleep overall. Therefore, this time transition, where it is lighter earlier in the day, may cause individuals to wake early in the morning, thereby creating healthier sleeping habits, which Crane suggested may lead to cognitive benefits, hormone cycle changes (ex. cortisol), food metabolism alterations and mental health improvements. 

While this is applicable to the entire population, this could potentially have more profound implications for Cornell’s athletic community. Crane mentioned an area of circadian rhythm biology that has gained a lot of attention deals with traveling athletic teams. When they travel to different time zones, this can alter behaviors and therefore athletes’ performance in a game. He explained that for individuals navigating to different time areas, there are strategies through which they can adapt to play ideally. Particularly paired with this national clock change, athletes with games this week would benefit from ensuring to travel to their game location a night before so their internal clocks may adjust and “reset” before they must play.

While many deliberate the wider implications of time changes and whether the clocks should be held constant at standard or daylight savings time, the foundational cause of all possible wellness implications revolves around circadian rhythms. 

“Your oscillator is trying to change those gene expression patterns and move them to follow the day-night cycle,” Crane said. “And so, if things are out of sync, and they haven’t been able to adjust, it takes one or two days for these things to shift.”

Ava Malkin can be reached at [email protected].