Four questions for Jamie Zeitzer on daylight saving time
The co-director of the Stanford Center for Sleep and Circadian Sciences dishes on the science (or lack thereof) behind “falling back.”
Last spring, the Senate voted in favor of a bill called the Sunshine Protection Act. It would have made daylight saving time permanent in the United States, but it’s stalled out in the House of Representatives. We asked Stanford sleep medicine scientist Jamie Zeitzer about the pros and cons of changing our clocks.
“We can’t create more sunlight. There is a finite number of hours,” said Zeitzer. “The question is, do you want them to start earlier or extend slightly later in the day?”
As a scientist in sleep and circadian research, do you think we should continue practicing daylight saving time?
There is abundant evidence that switching back and forth is bad for our health. Whether we should switch to permanent standard time or permanent daylight time is a bit more nuanced. There has only been one good study that looked at this directly. Researchers evaluated people on different sides of a time zone and observed that people on the eastern side, where the sun rose earlier, were healthier than people on the western side.
Why does the current movement call for a switch to permanent daylight time?
Lots of people are clamoring for a switch to permanent daylight time. A few years ago, a proposition in California received overwhelming support for making daylight time permanent, but without a change in federal law, it’s illegal. As it stands, states can choose between permanent standard time and changing the clocks twice a year. It’s difficult to gauge public opinion because a lot of the polls are biased by phrasing. They say things like, “Do you want permanent summertime or permanent wintertime?” which influences people’s answers.
A lot of the big proponents of permanent daylight time have economic reasons. With more daylight in the evenings, people might do more shopping or play more golf after work. I’m not an economist, so I can’t speak to that, but from a biological perspective it’s better to have an earlier sunrise.
How do circadian rhythms work?
Circadian rhythms are near 24-hour oscillations that help our bodies anticipate changes in the environment and behavior. These internal rhythms are synchronized to the outside world through regular light exposure. One of the main ways our internal clock remains synchronized with the world is through early morning light exposure. When we’re in daylight saving time from March to November every year, the sun rises at a later clock time than it otherwise would.
Keeping time in our bodies helps us make predictions. The central circadian clock predicts when you’re going to fall asleep, wake up, become hungry and even get sick. It acts like the conductor of an orchestra, helping to synchronize clocks all over the body.
What happens when our circadian rhythms are disrupted by an event like falling back or springing forward?
Remember the orchestra? If the conductor is not getting correct cues, then it won’t be able to make good predictions. Erratic sleep begets more erratic sleep because the clock can’t predict bedtime. You might experience disruption in your diet and energy levels.
The most obvious example is jet lag. Jet lag is when your internal clock is out of sync with the outside world, and you need to sync up through regular light exposure. The general rule of thumb is about a time zone per day to adapt. So basically, when you do this shift twice a year, you’re jumping a time zone. If you’re in Denver, your brain is either going to Chicago or San Francisco, depending on the season.
The thing is every time you shift your circadian clock there is a risk. You can think of it like buying a lottery ticket. Any individual is unlikely to win but with 330 million Americans participating, someone will. Unfortunately, in this case, the winning ticket can be a heart attack or disease. It is also problematic, especially for drivers, when everyone on the road is a little sleepier on the same day in the spring. For now though, you can try to prepare by adjusting your sleep in 15 minute increments before a big change. After the shift, get some early morning light as soon as you can to help your body adjust.
Zeitzer is a professor of psychiatry and behavioral sciences in the School of Medicine, and a member of Stanford Bio-X, the Wu Tsai Human Performance Alliance, the Maternal & Child Health Research Institute (MCHRI), and the Wu Tsai Neurosciences Institute.