Daylight saving time is here. On Sunday, at 2 a.m., everyone in the United States will set their clocks ahead an hour. Except Hawaii. And Arizona. And the Midway Islands. And, yet again, reporters have to slog through the slew of studies on whether daylight saving is useful at all. So here we go:


Here’s a raft of studies on the subject. Most of them find that while households do use less lighting during daylight saving, thanks to the longer, brighter afternoons, they also end up cranking up the air conditioning more, which makes it either a wash or a net loser for energy use. A 2008 paper (pdf) by economists Matthew Kotchen and Laura Grant examined what happened in Indiana when, thanks to a change in state law, all counties suddenly had to shift to daylight saving. They concluded that daylight saving probably costs Indiana about $10.7 million to $14.5 million per year in higher electricity bills and increased coal pollution.

Meanwhile, daylight saving doesn’t seem to impact gasoline use and driving habits one way or the other. Back in 2005, Congress decided to extend daylight saving by four weeks, claiming it would reduce oil use by 1 percent. A subsequent review (pdf) in 2008 by the Department of Energy found that the legislation didn’t appear to have any effect on gasoline consumption at all.

2) Daylight saving time might increase traffic fatalities. There’s also some dispute about whether daylight saving time increases or decreases traffic accidents. On the one hand, the extra hour of sunshine in the afternoon means that more people are driving while it’s still light out. That makes the roads safer, according to a 1995 study (pdf) in the American Journal of Public Health. On the other hand, the sleep disruptions that occur when clocks are moved forward can increase the risk of traffic fatalities during the spring. Back in 1996, researcher Stanley Coren found that traffic accidents flare up in the spring, when we set our clocks forward and everybody’s tired, and drop again in the fall, when we set our clocks back and get an extra hour of sleep.

3) Daylight saving can be bad for your health. Again, some mixed results here. The extra sunlight is good for vitamin D synthesis. But the disruption in sleep patterns caused by setting your clock forward can actually kill people. Here’s the finding reported in a brand new study out of the University of Alabama in Birmingham: “The Monday and Tuesday after moving the clocks ahead one hour in March is associated with a 10 percent increase in the risk of having a heart attack,” says researcher Martin Young. And a 2009 study (pdf) in the Journal of Applied Psychology found that tired workers are at greater risk of workplace accidents.

4) Daylight saving has mixed effects on the economy. Retailers love the extra sunlight — it means that there are more customers around who are willing to go out and shop. The all-powerful golfing industry is also a big fan, apparently. On the other hand, daylight saving can cut into sales for movie theaters and reduce the audience for prime-time television — people go out and enjoy the evening air instead of staring at screens inside.

So there you have it. Daylight saving: It kills people, it seems to be an energy-loser, and it leads to a slight uptick in road accidents in early March. On the other hand . . . who doesn’t enjoy a little more Vitamin D?