The impacts of time change


When Californians voted to make daylight saving time last year-round, they were voting to eliminate the twice-yearly change that people tend to like in the fall, when the clock is set back and we gain an hour of sleep, and dislike in the spring, when the clock is set an hour forward and we lose an hour in bed. Why is this important from the point of view of our health?

Studies have shown a 24 percent increase in heart attacks in the week after spring forward because of the loss of that hour of sleep, and a significant increase in fatal vehicle accidents in the week following the shift. Pedestrian deaths also increase. When the change occurs in the fall, with people gaining an hour of sleep, the opposite is true. Why was the vote to keep daylight saving time rather than standard time?  

Daylight saving time originated as an energy-saving measure during World War I and was adopted sporadically in peacetime. In 1966, amid confusion over a patchwork of schemes in each state for beginning and ending daylight saving, Congress stepped in with the Universal Time Act to standardize it nationwide. States could opt out of daylight saving time—it’s not observed in Hawaii because this state, the farthest south, doesn’t see a big difference in daylight hours between winter and summer months. Most of Arizona is on standard time all year, but not the Navajo Nation—which lies partly in New Mexico and Utah, states that make the changes. The Hopi Tribe within the Navajo Nation goes along with the rest of Arizona.  

Despite the fact that daylight saving time was introduced to save fuel, there isn’t strong evidence that the current system actually reduces energy use—or that making it year-round would do so either. 

Studies that evaluate the energy impact of daylight saving are mixed. It seems to reduce lighting use (and thus electricity consumption) slightly but may increase heating and air-conditioning use, as well as gas consumption. It’s probably fair to say that energy-wise, it’s a wash.   

Democratic Congressman Kansen Chu authored Proposition 7, which allows the state legislature, with a two-thirds vote, to make California’s daylight saving time last year-round, provided it is agreed to by the federal government. Currently it is not, though there is a Florida bill pending in Congress that could change that. 

Chu is satisfied that legislation will suffice to clear the federal hurdles, and said he’ll focus on winning over two-thirds of the state legislature, where some of his colleagues have argued things are fine the way they are. 

National Parent Teachers groups oppose permanent daylight saving because of safety concerns over children going to school in the dark. Chu initially suggested ditching daylight saving time and keeping standard time all year, but youth sports leagues said that would keep them from holding weekday practices and games after work and school because darkness would come too early. So Chu switched gears, and pushed for permanent daylight saving time instead.  

Obviously, this is a complicated issue, but here’s the take-home message. Sleep is a vitally important issue for your body, your heart, and your safety on the road. Resolve to get enough of it every day and go to bed an hour early before daylight saving time comes so you won’t suffer so much in the following week. Pay attention to jet lag; many people use melatonin to get them through the adjustment. If your friends pride themselves on how little sleep they need, start priding yourself on how much you enjoy a full seven to eight hours or more. Your brain and your body will thank you.


Sadja Greenwood, a longtime Bolinas resident now living in Portland, is a retired physician formerly active at the University of California, San Francisco. Her columns are back in the Light by popular demand.