Daylight Savings NZ: Is Daylight Saving Time Bad For Your Health
Quick Summary
The transition to Daylight Saving Time (DST) in the spring is associated with a measurable increase in the risk for several health problems in the following week.
Major areas of concern include a rise in heart attacks, injuries, mental and behavioral disorders (specifically substance use), and digestive system issues.
The study also uncovered a surprising finding: the risk for some infections and immune-related conditions appears to decrease immediately after the spring time change, possibly due to a short-term stress response.
Researchers estimate that each spring DST shift is linked to approximately 150,000 health problems in the United States alone.
Daylight Saving Time And Health
Twice a year, about a quarter of the world’s population changes their clocks for daylight savings (DST), disrupting sleep schedules for the sake of an extra hour of evening daylight.
While the debate over energy savings continues, a growing body of scientific evidence is asking a more pressing question: What is this shift doing to our health?
While previous studies had suggested links between daylight savings time and specific problems like heart attacks or traffic accidents, their results were often limited to a single condition and sometimes produced conflicting findings (Zhang et al., 2020).
To get a more comprehensive picture of the health risks - and any potential benefits - associated with the twice-yearly time shift, Zhang and colleagues analysed the health records of over 159 million people in two large health databases from the US and Sweden with the aim to move beyond single-issue research .
How Did They Study Daylight Saving And Health?
The researchers conducted the study by analyzing massive databases of electronic health records from two entire countries and comparing the number of medical diagnoses in the week after the DST shift to a normal, baseline period. The goal was to see if the rate of any particular illness changed significantly when the clocks were changed (Zhang et al., 2020).
Here’s a simple breakdown of their method:
Gathering Data: The team accessed two enormous, anonymized datasets: the IBM Watson Health MarketScan database, covering over 150 million insured individuals in the United States, and the Swedish national inpatient register, which includes health information for more than nine million people in Sweden.
Establishing a Baseline: To know if a change occurred, they first had to establish what a "normal" week looked like. They calculated the average diagnosis rate for each day of the week by looking at the two weeks before and the two weeks after the DST transition. This gave them a reliable expected rate for illnesses when there was no time-change disruption.
Comparing and Analyzing: They then measured the actual diagnosis rates for hundreds of different conditions during the week immediately following the spring and fall time changes. By comparing this "DST week" to the baseline, they could pinpoint any meaningful increases or decreases in health problems that were unlikely to be due to random chance.
Confirming the Findings: To be sure the effects were truly from the time change and not just a coincidence, they used several clever double-checks called negative controls. For instance, they analyzed health data from Sweden from before 1980 (the year the country adopted DST) and found no similar health spikes. They also looked at data from U.S. states that don't observe DST. In these control groups, the effects disappeared, confirming the link to the time change itself.
This large-scale, careful approach allowed the researchers to identify broad patterns of health effects with a high degree of confidence.
So, what did this massive health investigation find?
How Does the "Spring Forward" Daylight Saving Time Shift Affect Our Health?
Overall, the researchers estimated that the one-hour "spring forward" is linked to 150,000 health problems in the U.S. alone, and 880,000 globally each year (Zhang et al., 2020).
Essentially, the one-hour loss of sleep associated with the spring DST transition acts as a system-wide shock, leading to a significant increase in the risk for a range of health problems in the week that follows.
Which Health Problems Increase After the Spring Daylight Saving Time Change?
The study identified four main groups of health conditions that become more common after the spring time change:
cardiovascular diseases,
injuries,
mental health disorders, and
digestive issues (Zhang et al., 2020).
How Does Daylight Saving Time Change Affect Cardiovascular and Circulatory Problems?
The most well-documented risk associated with DST is its effect on the heart. The Zhang et al (2020) analysis confirmed earlier findings, showing a notable increase in heart conditions, particularly in adults over 60. This supports previous studies that found a rise of about 3.9 percent in heart attacks (Janszky et al., 2012).
But the risk isn't limited to the elderly. The study also noted an approximate 10 percent increase in the risk for some heart diseases among inpatients under 20 (Zhang et al., 2020). The sudden disruption to the sleep-wake cycle appears to place a sudden stress on the cardiovascular system.
Does The Daylight Saving Time Change Increase Accidents and Injuries?
It may not be surprising that losing an hour of sleep can make people less alert, but the consequences are stark. The study found a clear rise in injuries after the spring shift (Zhang et al., 2020). This aligns with previous studies that have linked the transition to more traffic accidents and a 5.7% increase in workplace injuries, as employees sleep an average of 40 minutes less the night after the change (Barnes & Wagner, 2009).
The new analysis further specified that children and young adults were more prone to injuries of the head, wrist, and hand, while older adults were more likely to injure their lower torso.
How Does The Daylight Saving Time Change Affect Mental Health Disorders?
One of the most significant new findings was the link between DST shifts and mental and behavioral health. Researchers in both the U.S. and Sweden observed a sharp increase in diagnoses related to psychoactive substance use, particularly among males over 20. The effect was significant, with risk increasing by as much as 9 percent after the spring shift and 12 percent after the fall shift in this group (Zhang et al., 2020).
The body's circadian clock is deeply connected to the brain's reward systems. A large body of research has shown that circadian disruption can increase the risk of substance abuse (Logan et al., 2014). It appears that the acute disruption from the DST shift may further destabilize an already vulnerable system, potentially leading to increased substance use.
Does The Daylight Saving Time Change Impact Digestive and Immune System Disorders?
For the first time, researchers also reported a DST-related increase in disorders involving the digestive system. For example, the risk for noninfective enteritis and colitis, which are types of intestinal inflammation, rose by 3 percent in females over 60 and 6 percent in males under ten (Zhang et al., 2020).
How?
The gut has its own internal clock that is closely tied to the brain's master clock, and disrupting this rhythm can affect digestive health. The study also noted an increase in other immune-related disorders, suggesting the time change can provoke an inflammatory response in the body.
Whose Health Is Most at Risk From the Daylight Saving Time Change?
The study found that the health risks associated with the daylight savings time shift are not distributed equally, with children, older adults, and individuals with chronic health conditions being the most vulnerable.
Researchers identified three groups that were particularly responsive to the disruption (Zhang et al., 2020):
The very young and older adults with chronic illnesses: People under 20 and those over 40 with pre-existing conditions showed a higher risk for issues like heart problems and stress-related immune disorders.
Children and teenagers prone to accidents: This group (ages 0-20) saw a specific increase in injuries to the head, wrist, and hand.
Older adults with injuries: Adults over 40 were more likely to suffer injuries to the lower torso or thorax.
But if the stress of the time change can cause some bodily system to overreact, could it also have the opposite effect on others?
From Zhang et al., 2020
Are There Any Positive Health Effects from Daylight Saving Time?
Surprisingly, the answer may be yes, though with an important caveat. The Zhang et al (2020) study that identified numerous health risks also discovered that the incidence of some diseases appears to decrease in the week after the spring daylight saving shift. These conditions were primarily infectious and inflammatory diseases, such as certain urinary tract and skin infections.
This finding seems counterintuitive. If the time change is a negative stressor, how could it possibly reduce the risk of getting sick?
How Could Losing Sleep Possibly Boost the Immune System?
The researchers suggest this protective effect may be explained by the difference between short-term and long-term stress. While chronic, long-term stress is known to suppress the immune system, a mild, short-term stressor can actually have the opposite effect, temporarily enhancing immune function (Dhabhar, 2014).
Think of it like your body’s “fight-or-flight” response. When faced with a brief challenge, the body mobilizes its defenses. The one-hour sleep loss from the DST shift may act as such a challenge, putting the immune system on high alert for a short period. This temporary boost could make the body more effective at fighting off certain infections in the days immediately following the time change (Zhang et al., 2020).
What Can You Do to Prepare for the Daylight Saving Time Change?
The evidence suggests that the abrupt shift in our sleep schedule is the primary driver of these health risks. While the debate over ending daylight saving time continues, the clocks are still changing for most of us. Here are a few practical steps you can take to ease the transition:
Adjust Your Sleep Schedule Gradually: In the days leading up to the "spring forward," try going to bed and waking up 15-20 minutes earlier each day. This helps your body clock adjust slowly rather than all at once.
Prioritize Light Exposure in the Morning: As soon as you wake up, get exposure to bright light. This is a powerful signal to your brain that helps reset your circadian rhythm and promotes wakefulness.
Be Extra Cautious: Given the increased risk of accidents and injuries, be particularly careful on the roads and at work in the days following the time change. Avoid taking on risky tasks if you feel drowsy.
Maintain a Consistent Routine: Stick to your regular meal times and exercise schedule as much as possible. These routines act as additional time cues or zeitgebers, that help anchor your internal clock.
Is It Time to Ditch Daylight Saving Time?
The original purpose of Daylight Saving Time was to save energy. But this saving is now considered too small to matter. Meanwhile, the evidence of its negative health consequences continues to grow. Organisations like the American Academy Of Sleep Medicine advocate for permanent standard time.
The disruption of our body's basic biological rhythms for a single hour has been shown to have measurable and sometimes serious effects on our cardiovascular, neurological, and immune systems. With an estimated 880,000 health problems across the world linked to each spring shift, the research raises a critical question: Is the cost of "springing forward" a price we should continue to pay?
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Frequently Asked Questions: Daylight Saving Time and Health
Q1: What are the main health problems linked to the spring Daylight Saving shift?
A1: The week after the "spring forward" time change is linked to an increased risk in four main areas. These include cardiovascular problems like heart attacks, a rise in accidents and injuries, mental and behavioral issues such as psychoactive substance use, and digestive system disorders like colitis (Zhang et al., 2020).
Q2: How significant are the health risks from daylight saving time shifts?
A2: While most risk elevations are modest, they are significant and important on a population-wide scale. For example, researchers estimate that each spring Daylight saving time shift is associated with about 150,000 health problems in the U.S. alone (Zhang et al., 2020). Specific findings from studies show a nearly 4% rise in heart attacks (Janszky et al., 2012), a 5.7% increase in workplace injuries (Barnes & Wagner, 2009), and up to a 9% increase in issues related to substance use in adult males following the spring shift (Zhang et al., 2020).
Q3: Is the "fall back" time change to standard time harmful?
A3: Yes. The "fall back" transition appears to have a different risk profile to the “spring forward” daylight saving time change. The study by Zhang et al (2020) found that the autumn shift is generally not associated with the same increase in heart attacks that we see in the spring. However, it is linked to a significant, and even larger, increase in diagnoses related to psychoactive substance use. The risk for these issues rose by 12% in adult males after the fall time change, compared to 9% in the spring (Zhang et al., 2020).
Q4: Who is most likely to be negatively affected by the daylight saving time changes?
A4: The study by Zhang et al (2020) identified three groups that appear to be the most vulnerable to the disruption caused by the DST shift:
The very young (under 20) and older adults (over 40), particularly those with pre-existing chronic diseases.
Children and teenagers, who showed a higher likelihood of injuries to the head, wrist, and hand.
Adults over 40, who were more likely to suffer injuries to their lower torso.
Q5: Can the daylight saving time change actually be good for the immune system?
A5: The study by Zhang et al (2020) noted a decrease in some infectious and inflammatory diseases, like urinary tract and skin infections, in the week after the spring shift. The researchers suggest this could be because the one-hour sleep loss acts as a mild, short-term stressor. Unlike chronic stress, which weakens the immune system, short-term stress can temporarily put it on high alert, making it better at fighting off some infections (Dhabhar, 2014). However, this potential benefit does not outweigh the many negative health effects observed.
Q6: What is the single best thing I can do to prepare for daylight saving time?
A6: The most effective strategy is to ease your body into the new time gradually. Instead of changing your schedule by a full hour overnight, adjust in small steps. For three to four days before the "spring forward," try going to bed and waking up 15-20 minutes earlier each day. This allows your internal body clock, or circadian rhythm, to adapt slowly and minimizes the shock to your system.
References
Barnes, C. M., & Wagner, D. T. (2009). Changing to daylight saving time cuts into sleep and increases workplace injuries. Journal of Applied Psychology, 94(5), 1305–1317.
Dhabhar, F. S. (2014). Effects of stress on immune function: the good, the bad, and the beautiful. Immunologic Research, 58(2-3), 193–210.
Janszky, I., Ahnve, S., Ljung, R., Mukamal, K. J., Gautam, S., Wallentin, L., et al. (2012). Daylight saving time shifts and incidence of acute myocardial infarction–Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA). Sleep Medicine, 13(3), 237-242.
Zhang, H., Dahlén, T., Khan, A., Edgren, G., & Rzhetsky, A. (2020). Measurable health effects associated with the daylight saving time shift. PLOS Computational Biology, 16(6), e1007927.
Written By The Better Sleep Clinic
Reviewed By Dan Ford, Sleep Psychologist
