To change or not to change… the time
A closer look at the costs and benefits to our health and performance
It’s that time again! Time to set our clocks forward and lose a delicious hour of the weekend. Last fall, I wrote about the fall time change and its effects on our health and productivity. This week, I would like to revisit this issue and examine the pros and cons of Daylight Saving Time in greater depth.
You will probably agree that changing our clocks twice a year is an inconvenience, one we tolerate in the name of saving energy. But what about the costs and benefits to our well-being and performance? Let’s take a closer look at the scientific evidence.
School
As I wrote previously, the spring time change is more disruptive to sleep than the fall one: it causes a stronger deterioration of sleep quality and increases night-time restlessness, and is particularly problematic for evening-type people, or “night owls” [1, 2]. Since teenagers have a biological tendency to be evening types, they tend to lose about 30 minutes of sleep on average per night during the week following the March time change, causing them to exhibit increased daytime sleepiness and decreased attention [3, 4]. As a result, experts recommend that schools not conduct any tests or major assessments in the week after the spring time change, since students will probably exhibit poorer performance than usual. [4]
Verdict: The transitions to (and from) DST disrupt teenagers’ sleep and school performance. If you are a high school student or the parent of one, see WebMD’s tips for maximizing good sleep during the time change. If you are a teacher or school administrator, try to postpone major tests for your students to another week if you can.
Work
However, loss of sleep after the spring time change is not limited to teenagers — adults also tend to get 40 minutes less sleep on the Monday following the change. [5] The resulting sleepiness and decreased attention could be dangerous in some jobs — for example, miners sustain more injuries and injuries of greater severity on the Monday after the time change. [5] Fortunately, it seems this disturbing effect is short-lived: when the entire week following the time change is examined, workplace injuries and occupational accidents are on average no more frequent than in the week before. [6,7]
Of course, many of us work in offices, sitting in front of computers rather than operating dangerous machinery. Yet office workers are affected too: the Monday after the spring time change sees an increase in cyberloafing, or goofing off online while at work, because of lost sleep. [8] Stranger still, the transition seems to have a negative effect on the stock market, although not all researchers agree on this. [9–12] Researchers have dubbed this the “daylight saving effect”: lower returns and higher volatility of the stock market on the Monday after the time change, presumably due to sleepier people being more anxious and risk-averse. [10, 12]
Verdict: Adults are more tired and less attentive on the Monday following the spring time change, but in most jobs, this effect is not seriously problematic. However, if you work in hazardous conditions, be extra careful this coming Monday. If you’re a supervisor, cut your employees some slack if you catch them browsing the web. And if you work with the stock market, expect a so-so day at the office on Monday.
Physical Activity
One of the reasons DST thought to be beneficial to human health is that the additional evening daylight may allow people to be more physically active after school or work. This seems to hold true for children [13], at least during the school year. For adults, the situation is more complicated, as it depends on whether they are biologically morning types or evening types. For example, morning people may prefer to exercise early in the morning, and DST may make that more difficult by reducing the daylight hours before the workday begins — but for evening types, the effect would be the opposite. [14]
Verdict: Overall, DST is beneficial for keeping kids physically active, and neutral for adults.
Clinical Consequences
Since good sleep is critical for well-being, the disruption of sleep schedules following the time change has raised concerns throughout the medical community about the possible adverse effects on various illnesses. For example, might the disruption lead to an overall increase in manic episodes in the days after the time change? Mercifully, the answer is no. [15] However, the time change does seem to affect cardiovascular patients: the first two days after DST transitions see more hospitalizations due to ischemic stroke [16], and in two out of the three countries where such studies have been conducted, the first three or four days after the time change show an increased incidence of heart attacks as well. [17, 18, 19]
Verdict: The disruption of sleep schedules by the time change is potentially dangerous to people with heart problems. If you are at risk for a heart attack or stroke, take a look at WebMD’s tips for maximizing good sleep during this transition.
Motor Vehicle Accidents
What about the effects of increased sleepiness on motor vehicle accidents? Fortunately, neither the week after the time change, nor even the first day show any increase in traffic accidents. [20, 21] On the contrary, analysis suggests that Daylight Saving Time leads to an overall reduction in car crashes due to improved evening visibility. [21] In fact, some researchers have put forward the idea of permanently switching to DST year-round, because this would reduce pedestrian and vehicle occupant fatalities. [22, 23]. Even animals might benefit, as DST seems to decrease the number of animal-vehicle collisions. [24]
Verdict: DST reduces the number of motor vehicle accidents.
Conclusion: Is DST good or bad for human health and productivity?
So is DST, with all its inconveniences, worth keeping? Here is a balance sheet of the pros and cons, from the most serious to the most minor:
Does the decrease in car crash fatalities compensate for the increased heart attacks? Unfortunately, we can’t say: the studies examining these two effects were done in different countries at different time periods, so it’s very difficult to compare them. Until someone conducts a comprehensive study looking at how all these factors balance out, we won’t know for sure whether DST is an overall benefit or an overall cost to our health and performance.
So… should you be worried? Well, if you are at risk for cardiovascular problems or work in a dangerous job — yes, a little. Stack the odds in your favor by being well-rested before the time change, and follow these tips. Otherwise, let’s face it: your greatest risk is most likely being very cranky on Monday.
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Sources
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[2] Lahti, T.A. et al. (2008). Transitions into and out of daylight saving time compromise sleep and the rest-activity cycles. BMC Physiology 8(3). doi:10.1186/1472–6793–8–3
[3] Medina, D. et al. (2015). Adverse effects of Daylight Saving Time on adolescents’ sleep and vigilance. Journal of Clinical Sleep Medicine 11(8): 879–884
[4] Schneider, A.M. and C. Randler. (2009). Daytime sleepiness during transition into daylight saving time in adolescents: Are owls higher at risk? Sleep Medicine 10(9): 1047–50
[5] Barnes, C.M. and D.T. Wagner. (2009). Changing to daylight saving time cuts into sleep and increases workplace injuries. Journal of Applied Psychology 94(5):1305–17
[6] Morassaei, S. and P.M. Smith. (2010). Switching to Daylight Saving Time and work injuries in Ontario, Canada: 1993–2007. Occupational and Environmental Medicine 67(12):878–80
[7] Lahti, T.A. et al. (2011). Work-related accidents and daylight saving time in Finland. Occupational Medicine 61:26–28
[8] Wagner, D.T. et al. (2012). Lost sleep and cyberloafing: Evidence from the laboratory and a daylight saving time quasi-experiment. Journal of Applied Psychology 97(5):1068–76
[9] Berument, M.H. et al. (2010). Effects of daylight-saving time changes on stock market volatility. Psychological Reports 106(2): 632–640
[10] Kamstra, M.J. et al. (2010). Effects of daylight-saving time changes on stock market volatility: A comment. Psychological Reports 107(3):877–887
[11] Berument, M.H. and N. Dogan. (2011). Effects of daylight-saving time changes on stock market volatility: A reply. Psychological Reports 109(3):863–878
[12] Kamstra, M.J. et al. (2013). Effects of daylight-saving time changes on stock market volatility: A rebuttal. Psychological Reports 112(1):89–99
[13] Goodman, A. et al. (2014). Daylight saving time as a potential public health intervention: an observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries. International Journal of Behavioral Nutrition and Physical Activity 11:84
[14] Rosenberg, M. and L. Wood. (2010). The power of policy to influence behaviour change: daylight saving and its effect on physical activity. Australian and New Zealand Journal of Public Health 34: 83–88
[15] Lahti, T.A. et al. (2008). Daylight saving time transitions and hospital treatments due to accidents or manic episodes. BMC Public Health 8:74
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[18] Sipila, J.O. et al. (2016). Association of daylight saving time transitions with incidence and in-hospital mortality of myocardial infarction in Finland. Annals of Medicine 48(1–2):10–6
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