How Daylight-Saving Time Impacts Health & Routine

One hour out of a 24-hour period represents 3,600 seconds, or 4% of the day. This doesn't sound like much, however, springing forward or falling backward by an hour, twice a year, carries a far greater impact than we may realize. According to research, more than 1.5 billion people are impacted by the time change (Smith, 2016), but our understanding of just how significant that impact remains uncertain.

Disrupted Rhythm

The human body and its physiology -- down to the microscopic levels of our cells -- thrives on a cadence, a rhythm. Daylight saving time (DST) disrupts this cadence and sends the body into an adjustment cycle that takes more than a single night's sleep to acclimate to.

Imagine the processes of the human body and how we go about our day-to-day schedules as two rows of dominoes. DST is a biannual outside force that knocks these two rows down and requires us to reconfigure how we function.

The Domino Effect

Sleep

When the clock either shifts backwards an hour or forwards an hour, the most disrupted aspect of an individual's routine is their sleep patterns. The body has a natural 24-hour circadian rhythm. While this cycle is internal, it is influenced by the environment, medications, and behaviors/habits. When DST occurs, it is not uncommon to experience additional fatigue, lack of focus or trouble concentrating, and mood changes due to lack of sleep or disrupted patterns.

Mood Changes & Cognition

As a result of the time changes, many individuals experience higher irritability, agitation, and impaired decision-making. For example, more medical errors and workplace injuries occur after clocks are set forward in the spring (AARP).

Hormonal Shifts

Because sleep is negatively impacted by the shifting of time, temporary hormonal shifts occur. The circadian rhythm, or the sleep cycle, controls the release of specific hormones in the body that are related to mood, hunger, and sleep. As a result, the body can experience discomfort and pain. "Cluster headaches", feelings of increased hunger (due to increased ghrelin presence and suppression of leptin), and difficulty sleeping or falling asleep due to melatonin alterations.

Appetite Changes and Increased Caffeine

It is not uncommon to feel hungrier than normal for about a week after the time shifts -- not just because of poor or disrupted sleep, but also due to the shifting of mealtimes to align with the time change. Further, during DST, individuals tend to consume additional caffeine and comfort foods to compensate for the increased fatigue and lethargy.

Adverse Health Events

We understand body rhythms and physiological processes are impacted (often negatively), but how far reaching do these consequences spread?

Some research has indicated DST has an impact on motor vehicle crashes. Smith (2016) published an article in the American Economic Journal: Applied Economics that implied that from 2002–2011, the transition into DST caused over 30 deaths. Smith (2016) highlighted the estimated social cost to be $275 million annually. The author, using the American Time Use Survey (2009) found that Americans sleep 40 minutes less on the night of the fall transition. However, there is no consensus on these findings.

According to the American Heart Association, the time change carries potential consequences for the heart. Atrial fibrillation (Afib) (the most common type of irregular heartbeat) episodes increase with time transitions. Research also indicates that the Monday following the springtime change (losing an hour of sleep) was associated with a 24% increase in daily heart attack counts. On the Tuesday following the fall time change (gaining an hour of sleep) was associated with a 21% reduction in heart attacks (Sandhu, Seth, & Gurm, 2014)

Other research (Johnson & Malow, 2022) highlights a short-term increase in stroke (in susceptible populations), and increased depression after the spring transition in March.

Even the American Academy of Sleep Medicine is in favor of abolishing any further time changes and has advocated for standard time to become permanent. In their position statement, the Academy took a powerful stance by stating:

"Daylight saving time incurs significant public health and safety risks, including increased risk of adverse cardiovascular events, mood disorders, and motor vehicle crashes. Although chronic effects of remaining in daylight saving time year-round have not been well studied, daylight saving time is less aligned with human circadian biology-which, due to the impacts of the delayed natural light/dark cycle on human activity, could result in circadian misalignment, which has been associated in some studies with increased cardiovascular disease risk, metabolic syndrome and other health risks" (Rishi, et al, 2020).

One hour out of a 24-hour period represents 3,600 seconds, or 4% of the day. The research highlighted in this article makes us rethink the power of the hour. Whether or not DST will become a thing of the past remains uncertain, but what is not questionable is the significant impact a biannual time change has on the human body.

References

AARP American Heart Association Johnson & Malow, 2022 News Medical Life Sciences Northwestern Medicine Rishi, et al., 2020 Sandhu, Seth, & Gurm, 2014) Smith, 2016 *

Dr. Erin Nitschke is a professor of exercise science at Laramie County Community College. She holds certifications including NFPT-CPT, NSCA-CPT, ACE Health Coach, Fitness Nutrition Specialist, Therapeutic Exercise Specialist, and Pn1. Erin is an editorial author for IDEA, NFPT, where she writes regularly on topics related to personal training and health coach skill building, behavior change, and career success.