Now, a study by Stanford Medicine researchers finds there are longer-term hazards as well -- and better alternatives.

The researchers compared how three different time policies -- permanent standard time, permanent daylight saving time and biannual shifting -- could affect people's circadian rhythms, and, in turn, their health throughout the country. Circadian rhythm is the body's innate, roughly 24-hour clock, which regulates many physiological processes.

The team found that, from a circadian perspective, we've made the worst choice. Either permanent standard time or permanent daylight saving time would be healthier than our seasonal waffling, with permanent standard time benefitting the most people.

Indeed, by modeling light exposure, circadian impacts and health characteristics county by county, the researchers estimate that permanent standard time would prevent some 300,000 cases of stroke per year and result in 2.6 million fewer people having obesity. Permanent daylight saving time would achieve about two-thirds of the same effect.

"We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year," said Jamie Zeitzer, PhD, professor of psychiatry and behavioral sciences and senior author of the study to publish Sept. 15 in the Proceedings of the National Academy of Sciences. The lead author is Lara Weed, a graduate student in bioengineering.

A theory lacking data

Even among people who want to end seasonal time shifts, there's disagreement over which time policy to adopt.

"You have people who are passionate on both sides of this, and they have very different arguments," Zeitzer said.

Supporters of permanent daylight saving time say more evening light could save energy, deter crime and give people more leisure time after work. Golf courses and open-air malls are big proponents, Zeitzer said. A trial of permanent daylight saving time begun in 1974, however, was so unpopular it was abandoned after less than a year. Among the objectors were parents worried about their children going to school in the dark.

Nevertheless, the duration of daylight saving time was later increased from six months to seven months. And since 2018, a bill proposing permanent daylight saving time has been introduced in Congress nearly every year, though it has never passed.

In the other camp, proponents of permanent standard time contend that more morning light is optimal for health. Organizations such as the American Academy of Sleep Medicine, the National Sleep Foundation and the American Medical Association have endorsed year-round standard time.

"It's based on the theory that early morning light is better for our overall health," Zeitzer said of these endorsements. "The problem is that it's a theory without any data. And finally, we have data."

Syncing to 24 hours

The human circadian cycle is not exactly 24 hours -- for most people, it's about 12 minutes longer -- but it can be modulated by light.

"When you get light in the morning, it speeds up the circadian cycle. When you get light in the evening, it slows things down," Zeitzer said. "You generally need more morning light and less evening light to keep well synchronized to a 24-hour day."

An out-of-sync circadian cycle has been associated with a range of poor health outcomes.

"The more light exposure you get at the wrong times, the weaker the circadian clock. All of these things that are downstream -- for example, your immune system, your energy -- don't match up quite as well," Zeitzer said.

The researchers used a mathematical model to translate light exposure under each time policy, based on local sunrise and sunset times, to circadian burden -- essentially, how much a person's innate clock has to shift to keep up with the 24-hour day.

They found that over a year, most people would experience the least circadian burden under permanent standard time, which prioritizes morning light. The benefits vary somewhat by a person's location within a time zone and their chronotype -- whether they prefer early mornings, late nights or something in between.

Counterintuitively, people who are morning larks, who make up about 15% of the population and tend to have circadian cycles shorter than 24 hours, would experience the least circadian burden under permanent daylight savings time, as more evening light would extend their circadian cycles closer to 24 hours.

Health implications

To link circadian burden to specific health outcomes, the researchers analyzed county-level data from the Centers for Disease Control and Prevention on the prevalence of arthritis, cancer, chronic obstructive pulmonary disease, coronary heart disease, depression, diabetes, obesity and stroke.

Their models show that permanent standard time would lower the nationwide prevalence of obesity by 0.78% and the prevalence of stroke by 0.09%, conditions influenced by circadian health. These seemingly small percentage changes in common conditions would amount to 2.6 million fewer people with obesity and 300,000 fewer cases of stroke. Under permanent daylight time, the nationwide prevalence of obesity would decrease by 0.51%, or 1.7 million people, and stroke by 0.04%, or 220,000 cases.

As expected, the models predicted no significant difference in conditions such as arthritis that have no direct link to circadian rhythms.

Not the last word

The study might be the most evidence-based analysis of the long-term health implications of different time policies, but it's far from the last word, Zeitzer said.

For one thing, the researchers didn't account for many factors that could influence real-life light exposure, including weather, geography and human behavior.

In their calculations, the researchers assumed consistent and relatively circadian-friendly light habits, including a 10 p.m. to 7 a.m. sleep schedule, sunlight exposure before and after work and on weekends, and indoor light exposure from 9 a.m. to 5 p.m. and after sunset. But in reality, many people have erratic sleep schedules and spend more time indoors.

"People's light habits are probably much worse than what we assume in the models," Zeitzer said. "Even in California, where the weather is great, people spend less than 5% of their day outside."

Moreover, though circadian health seems to favor permanent standard time, the results are not conclusive enough to overshadow other considerations. Zeitzer hopes the study will encourage similar evidence-based analyses from other fields, such as economics and sociology.

He also points out that time policy is simply choosing which clock hours represent sunrise and sunset, not altering the total amount of light there is. No policy will add light to the dark winter months.

"That's the sun and the position of Earth," he said. "We can't do anything about that."

The study received funding from the National Institutes of Health (grant F31HL170715).

The finding, published on Aug. 29 in JAMA Network Open, highlights a gap in medical care for 4- and 5-year-olds with ADHD. Treatment guidelines recommend that these young children and their families try six months of behavior therapy before starting ADHD medication.

But pediatricians often prescribe medication immediately upon diagnosis, according to an analysis of medical records from nearly 10,000 young children with ADHD who received care in eight pediatric health networks in the United States.

"We found that many young children are being prescribed medications very soon after their diagnosis of ADHD is documented," said the study's lead author, Yair Bannett, MD, assistant professor of pediatrics. "That's concerning, because we know starting ADHD treatment with a behavioral approach is beneficial; it has a big positive effect on the child as well as on the family."

In addition, stimulant medications prescribed for the condition cause more side effects in young patients than they do in older children, Bannett said. Before age 6, children's bodies don't fully metabolize the drugs.

"We don't have concerns about the toxicity of the medications for 4- and 5-year-olds, but we do know that there is a high likelihood of treatment failure, because many families decide the side effects outweigh the benefits," he said. Stimulant medication can make young children more irritable, emotional and aggressive.

ADHD is a developmental disorder characterized by hyperactivity, difficulty paying attention and impulsive behavior.

"It's important to catch it early because we know these kids are at higher risk for having academic problems and not completing school," Bannett said. Early identification and effective treatment for ADHD improve children's academic performance. Research has shown that good treatment also helps prepare individuals with ADHD for many aspects of adulthood, such as maintaining employment, having successful relationships and avoiding trouble with the law.

Complementary treatments

Behavioral therapy and medication, the two mainstays of ADHD treatment, have different purposes.

"Behavioral treatment works on the child's surroundings: the parents' actions and the routine the child has," Bannett said. The therapy helps parents and kids build skills and establish habits compatible with how the child's brain works.

The evidence-based behavioral treatment recommended by the American Academy of Pediatrics is called parent training in behavior management. The training helps parents build strong, positive relationships with their children; offers guidance in rewarding a child's good behaviors and ignoring negative behaviors; and recommends tools that help kids with ADHD, such as making visual schedules to help them stay organized.

In contrast, medication relieves ADHD symptoms such as hyperactivity and inattentiveness, with effects that wear off as the body breaks down each dose of the drug.

Both approaches are needed for most kids with ADHD to do well. But previous studies of preschoolers diagnosed at age 4 or 5 show that it's best to start with six months of behavioral treatment before prescribing any medication.

Rapid prescriptions

The researchers analyzed data from electronic health records for children seen at primary care practices affiliated with eight U.S. academic medical centers. They began with 712,478 records from children who were 3, 4 or 5 years old and were seen by their primary care physician at least twice, over a period of at least six months, between 2016 and 2023.

From these records, the scientists identified 9,708 children who received an ADHD diagnosis, representing 1.4% of the children in the initial sample. They found that 42.2% of these children -- more than 4,000 kids -- were prescribed medication within a month of their ADHD diagnosis. Only 14.1% of children with ADHD first received medication more than six months after diagnosis. The researchers did not have access to data on referrals to behavioral therapy, but since young children are supposed to try the therapy alone for six months before receiving medication, any who were prescribed medication sooner were likely not being treated according to academy guidelines. A smaller study of recommendations for behavior therapy, published in 2021, found only 11% of families got the therapy in line with guidelines.

Children who were initially given a formal diagnosis of ADHD were more likely to get medication within the first 30 days than those whose medical charts initially noted some ADHD symptoms, with a diagnosis at a later time. But even among preschoolers who did not initially meet full criteria for the condition, 22.9% received medication within 30 days.

Barriers to behavioral treatment?

Because the study was based on an analysis of electronic medical records, the researchers could not ask why physicians made the treatment decisions they did. However, Bannett's team had informal conversations with physicians, outside the scope of the study, in which they asked why they prescribed medication.

"One important point that always comes up is access to behavioral treatment," Bannett said. Some locales have few or no therapists who offer the treatment, or patients' insurance may not cover it. "Doctors tell us, 'We don't have anywhere to send these families for behavioral management training, so, weighing the benefits and risks, we think it's better to give medication than not to offer any treatment at all.'"

Bannett said he hopes to educate primary care pediatricians on how to bridge this gap. For example, free or low-cost online resources are available for parents who want to learn principles of the behavioral approach.

And while the study focused on the youngest ADHD patients, behavioral management therapy also helps older children with the diagnosis.

"For kids 6 and above, the recommendation is both treatments, because behavioral therapy teaches the child and family long-term skills that will help them in life," Bannett said. "Medication will not do that, so we never think of medication as the only solution for ADHD."

Researchers contributed to the study from the Children's Hospital of Philadelphia, the Perelman School of Medicine at the University of Pennsylvania, Nationwide Children's Hospital, The Ohio State University College of Medicine, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Texas Children's Hospital, Baylor College of Medicine, Ann and Robert H. Lurie Children's Hospital of Chicago, Children's Hospital of Philadelphia, the University of Colorado, and Nemours Children's Hospital. `

This work was supported by the Stanford Medicine Maternal and Child Health Research Institute; the National Institute of Mental Health (grant K23MH128455); and the National Heart, Lung, and Blood Institute (grant K23HL157615). The study was conducted using PEDSnet, A Pediatric Clinical Research Network. PEDSnet was developed with funding from the Patient-Centered Outcomes Research Institute.