A tilt in the Earth's axis means significant changes in day length during the year for much of the world.
Credit: Ron Garan
As daylight saving time ends at 2 a.m. this coming Sunday morning (Nov. 3), most Americans will join snoozers across more than 60 other nations in savoring the gift of one extra hour of sleep.
Though the biannual ritual of turning clocks might feel like second nature to us today, it is actually a fairly new phenomenon that has only taken effect on a global scale within the past several decades (though many countries including Venezuela, Kenya and Saudi Arabia still don't partake in it today).
Benjamin Franklin suggested the idea back in 1784, as a way to economize on sunlight and burn fewer candles during winter mornings and nights, but the practice did not become steadily official in the United States until Congress passed the Uniform Time Act in 1966, with the same intention of saving energy. [5 Fun Facts About Daylight Saving Time]
Whether or not the practice actually shrinks energy bills seems to vary from state to state and remains up for debate today. What seems more certain, however, is that the subtle time shift can take a noticeable toll on the human body. Here are the five strangest ways that daylight saving time, and the ending of it, affect human health:
1. More car accidents?
An increase in car accidents during daylight saving time has been both supported and refuted in the academic literature. The general concept supporting the case, however, is that subtle changes in sleep patterns and circadian rhythms can alter human alertness and, in some cases, might increase the risk of potentially fatal car accidents.
Still, one 2010 Journal of Environmental Public Health study that analyzed the number of traffic accidents in Finland one week before and one week after transitions into and out of daylight saving time from 1981 through 2006 found no significant change in the number of accidents during this time period. Another 2010 study published in the Journal of Safety Research found that daylight saving time can actually result in fewer crashes by increasing visibility for drivers in the morning.
2. Increased workplace injuries
Though this threat may not apply to those who work in the relatively padded confines of carpeted office buildings, others who work at more physically taxing jobs, such as miners, have been shown to experience more frequent and severe workplace injuries at the onset of daylight saving time in the spring. The effect has not been detected at the end of daylight saving time in the fall.
The 2009 Journal of Applied Psychology study that came to this conclusion found that mine workers arrived at work with 40 minutes less sleep and experienced 5.7 percent more workplace injuries in the week directly following the springtime daylight saving transition than during any other days of the year. The researchers attribute the injuries to lack of sleep, which might explain why the same effect did not pop up in the fall when workers gained an hour of sleep. [Top 10 Spooky Sleep Disorders]
3. More heart attacks
A team of Swedish researchers conducted a study in 2008 that showed the rate of heart attacks during the first three weekdays following springtime daylight saving time increased by about 5 percent from the average rate during other times of the year. As with workplace injuries, the effect did not arise at the end of daylight saving time in the fall.
In the 2008 New England Journal of Medicine article that described this pattern, the researchers attributed the small surge in heart attacks in the springtime to changes in people's sleep patterns. Lack of sleep can release stress hormones that increase inflammation, which can cause more severe complications in people already at risk of having a heart attack.
4. Longer cyberloafing
Cyberloafing — the slang word for surfing the Web for personal entertainment during work hours — may not be as life-threatening as heart attacks and workplace injuries, but it can cost companies thousands of salary wages flushed down the Internet tube.
A 2012 Journal of Applied Psychology study found that the incidence of cyberloafing significantly increased in more than 200 metropolitan U.S. regions during the first Monday after daylight saving time in the spring, compared with the Mondays directly before and one week after the transition. The team attributed the shift to a lack of sleep and thus lack of workday motivation and focus, but was not able to verify this experimentally.
5. Increased cluster headaches
Circadian rhythms tick away throughout the body each day, controlling the release of certain hormones that affect moods, hunger levels, and yearning for sleep. When these rhythms get thrown out of whack, even by just one hour during daylight saving time, the human body notices the difference.
For some people, the effects of this change can set off debilitating chronic pain. Cluster headaches, for example — or headaches that cluster within one side of a person's head and can cause excruciating pain for days or weeks at a time — seem to be triggered by changes in circadian rhythms, including during the transitions in and out of daylight saving, the New York Daily News reported Friday (Nov. 1).
Why, exactly, the change in rhythms has this effect remains unclear.