Why permanent daylight saving time may not be the best option
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Story highlights
- Congress is currently considering whether to end twice-a-year clock changes
- ASU sleep scientist Megan Petrov says permanent standard time is the best option.
- Adopting permanent daylight saving time could contribute to insufficient sleep, poorer health, reduced performance and safety concerns.
If you could choose where to place an hour of daylight, would you rather wake up with the sun or get off work while it’s still shining?
That question is at the center of a debate before Congress this session, as U.S. lawmakers consider ending the semiannual ritual of changing the clocks. Arizona State University sleep scientist Megan Petrov says they are right to call for an end to the seasonal disruption.
But they may be going about it the wrong way.
Petrov, an associate professor in ASU’s Edson College of Nursing and Health Innovation, is a clinical psychologist whose lab studies the role of sleep and circadian rhythms in the development of chronic disease across the lifespan.
“I am absolutely for the ending of seasonal clock changes,” said Petrov, who has lived both in Arizona, which observes permanent standard time, as well as states that follow daylight saving time. “But where (lawmakers) are getting things wrong is that they want to propose permanent daylight saving time, whereas the better option is permanent standard time.”
Permanent daylight saving time means the country would stay on the spring-summer schedule all year. It does not create more daylight; instead, it shifts an hour of daylight from the morning to the evening, so that the sun rises later in the morning and sets later in the evening, giving people more light after work or school. But that means darker mornings, which can make it harder for bodies to wake up.
Permanent standard time means the country would stay on “normal” time all year. The sun would rise earlier in the morning and set earlier in the evening.
Petrov says the reason she prefers the latter comes down to biology: Permanent standard time is better aligned with the body’s circadian rhythms — the internal clocks that help regulate sleep, hormones, metabolism and other essential functions — which morning sunlight plays a critical role in synchronizing.
Morning or evening sun — which is better?
A common misunderstanding when it comes to daylight saving time — and perhaps the reason behind its appeal — is that we’re gaining an extra hour of daylight. (We’re not; instead, that extra hour of daylight is simply shifted from the morning to the evening.)
“While that can sound very attractive to a lot of people, it’s not what our bodies need,” she said. “Our bodies need morning light to synchronize our body clocks so that our bodily systems can function on a regular rhythm.”
The springtime change, when clocks move forward and people lose about an hour of sleep, has been linked to health and safety risks. Petrov said the shift affects everyone, but some groups are especially vulnerable, including children, teenagers, older adults and morning commuters.
Adolescents may be hit particularly hard, she said. Teenagers already tend to have later sleep schedules because of natural biological changes, and many are chronically sleep-deprived. More evening light under permanent daylight saving time could push bedtimes even later, while school start times would likely remain the same.
“They still have to get up for school,” Petrov said. “They still have to get there on time.”
That could mean more students commuting in the dark and arriving at school with less sleep, making it harder for them to learn, focus and perform well.
Older adults and people with existing health risks may also be affected. Petrov noted that heart attacks and strokes are more likely to occur in the morning, and the loss of sleep during the spring shift has been associated with increased health risks. Traffic accidents also rise after the time change, making the transition a concern for commuters.
Although permanent daylight saving time is often promoted as a way to give people more usable evening light for shopping, dining and outdoor activities, Petrov said those benefits come with hidden costs.
If the country adopted permanent daylight saving time, Petrov said, the mismatch between the clock on the wall and the sun would persist all year. Over time, that could contribute to insufficient sleep, poorer health, reduced performance and safety concerns.
For people preparing for seasonal clock changes, Petrov recommends gradually adjusting sleep and wake times in the days leading up to the shift. Going to bed and waking up a little earlier or later, depending on the direction of the time change, can help the body adapt.
The most important tool, she said, is morning light.
“Morning light is going to wake you up more quickly and help you function at the best that you can be,” Petrov said.
For Petrov, the debate is not simply political or economic. It is a public health issue rooted in the importance of sleep.
“It is not an absolute economic issue, even though there's the argument that you might get one hour of extra daylight in the evening that would drive up shopping and spending at restaurants and outdoor events and all of the things that we find attractive,” she said. “But it's still going to lead to a cost. It's not going to be a national net benefit for us all.
“Sleep is universally important for us all,” she said. “It is vital for us to be able to remember, to make really good decisions for our families and for ourselves, and for our long-term health.”
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