Article In Brief
Leading medical associations support the end of daylight saving time and a move to permanent standard time, which they say will better align with people’s natural circadian rhythm.
The American Medical Association (AMA), the American Academy of Sleep Medicine, and leading sleep neurologists are calling for an end to daylight saving time (DST) and moving permanently to year-round standard time. The AMA’s House of Delegates endorsed that position in a statement at its interim meeting in November 2022.
Other medical organizations calling for a move to permanent standard time include the American College of Chest Physicians, the Society of Anesthesia and Sleep Medicine, and the American Academy of Cardiovascular Sleep Medicine.
In a statement from the AMA, Trustee Alexander Ding, MD, MA, MBA, said: “For far too long, we’ve changed our clocks in pursuit of daylight, while incurring public health and safety risks in the process. Committing to standard time has health benefits and allows us to end the biannual tug of war between our biological and alarm clocks.”
The AAN Sleep Medicine Section has asked the AAN Board of Directors to make a similar statement, a proposal still under consideration, according to AAN President Orly Avitzur, MD, MBA, FAAN.
“The AAN is currently reviewing the scientific evidence in support of permanent standard time as we prepare for the upcoming state and federal legislative sessions,” Dr. Avitzur told Neurology Today.
The AAN Sleep Section hopes for that support, owing to an increasing body of evidence pointing to the detrimental health effects of the “spring forward, fall back” shifts between standard time and DST, according to Karin G. Johnson, MD, FAAN, an associate professor of neurology at UMass Chan Medical School—Baystate and chair of the AAN Sleep Medicine Section.
“Some of the largest impacts are increased rates of heart attacks, strokes, and traffic accidents,” Dr. Johnson said. “The main issues are in the spring, when we lose an hour of sleep and are going from standard time, which is more aligned with the sun, to DST, which is less aligned with the sun and natural circadian rhythms. People tend to lose about half an hour of sleep on average that is greatest in the first few days after the spring shift, but for many people, sleep remains disrupted throughout the entire DST period.”
A 2016 study in Sleep Medicine found that hospitalizations for stroke significantly increased during the first two days after both the spring and fall transitions, with a relative risk of 1.08, while research also has shown a link between the spring transition and increased hospitalization rates for heart attacks and atrial fibrillation. Because circadian rhythms are involved with the release of hormones including melatonin, cortisol, leptin, and ghrelin—which are related to stress, metabolism, and inflammation—disrupting these rhythms can increase the risk of metabolic and cardiovascular diseases as well as cancer progression, Dr. Johnson said.
In the largest study yet to examine associations between traffic accidents and clock shifting, involving more than 700,000 motor vehicle accidents, the risk of fatal accidents increased modestly during the spring DST transition, especially in the morning and in locations further west in a time zone.
“People assume that when it’s light out later, you will have fewer car accidents, but a 2022 study [in the journal Time & Society] looking at the long-term effects of living with the wrong clock time showed that any of that effect is erased by being misaligned with our natural circadian rhythms. This is probably because we are more likely to drive while sleepy or make poorer decisions like drunk driving, speeding, or texting while driving,” Dr. Johnson said. “All those cognitive effects outweigh any benefits we might have from more light later in the day.”
The “spring forward, fall back” shifts can be particularly disruptive and detrimental for people with neurologic conditions.
“I take care of kids and adults on the autism spectrum with sleep issues, and that group in particular has found that any sort of change in their routine throws them off,” said Beth A. Malow, MD, MS, FAAN, professor of neurology and pediatrics, director of the Vanderbilt Sleep Division, and the Burry Endowed Chair in Cognitive Childhood Development at Vanderbilt University Medical Center.
Dr. Malow is the lead author of a new paper from the Sleep Research Society calling for permanent year-round ST. She said she has spoken to others with a variety of neurologic conditions, “and they say they just feel off around the time change.”
“Many neurologic conditions have circadian and sleep/wake disorder aspects,” said Logan D. Schneider, MD, a clinical assistant professor at Stanford Health Care and former chair of the AAN Sleep Medicine Section.
“Headache [attacks] like migraine and cluster headache can be triggered by sleep/wake disruptions,” he said. “With other neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, we have the phenomenon of ‘sundowning,’ which can be triggered by poor stimulus of circadian rhythms. The loss of neurons associated with these conditions means that these patients do not have as strong a natural circadian rhythm to begin with, and the additional hit of arbitrary dysfunction from the DST transition and lack of adequate light stimulation can promote overactivity and behavioral issues at night.”
Permanent Standard Time vs. Permanent DST
Many Americans agree with abolishing the “spring forward, fall back” switch, according to a 2021 poll by the Associated Press-NORC Center for Public Affairs Research at the University of Chicago. Seventy-five percent of 1,083 respondents said they would like to stop switching their clocks twice a year, but they were about evenly divided on whether they would prefer permanent DST or permanent standard time. As the push grows for settling on one time and sticking to it, much of the emphasis has focused on moving to year-round DST, a position with which many sleep specialists do not agree.
In 2022, the US Senate passed a bill to establish permanent DST, dubbed the Sunshine Protection Act, and 20 states also endorsed year-round DST, although those state-level changes cannot take effect without Congressional action.
Proponents of year-round DST argue that the long, lingering daylight hours of summer and early fall encourage kids, and adults who work a regular 9-to-5 schedule, to be more physically active outdoors during the week. Dr. Johnson, however, cited a 2014 study in the Journal of Physical Activity & Health that found no difference in activity patterns between people living in Colorado, Utah, and New Mexico and residents of Arizona, a state which opted out of the federal Uniform Time Act of 1966 and stuck with PST because of the punishing afternoon desert heat. Proponents also cited potential energy savings and beneficial effects on the economy from dining out, shopping, and other consumer spending activities.
“People say, ‘I like my light in the afternoon,’ especially those who have the luxury of not having to be somewhere like work or school in the early morning,” Dr. Malow said.
But sleep experts argue that those preferences and potential benefits are strongly outweighed by the ongoing circadian misalignment that would result from permanent DST.
“The chronic detrimental effects of being misaligned for almost eight months out of the year are probably even more significant than the acute effects of the shifting back and forth,” Dr. Malow said. She noted that if DST became permanent, many locations wouldn’t see sunrise until nearly 9 a.m. during the first two weeks of January, the time of the year when mornings are darkest.
“One of the reasons we see more of the detrimental health effects of the DST-standard time shift in the spring, when we spring forward, is not just because we’re losing an hour of sleep, although that’s a factor,” Dr. Johnson said. “It’s also because we’re transitioning to a time that is less favorable for most people.”
The potential benefits of later light are likely the most in the spring and in fall, but there is no evidence that year-round those benefits remain. In fact, a 2011 study in the Review of Economics and Statistics reported an increase in energy use and utility bills because of increases in heating and cooling costs during daylight saving time, Dr. Johnson noted, and there are negative impacts to the overall economy because of the workforce being less productive, safe, and healthy.
Most people have a natural biological clock that actually runs slightly longer than 24 hours—about 24 hours and 11 minutes. “Every single day, we’re fighting an uphill battle to fall asleep and wake up on time, and every day we have a natural instinct to stay up a little later,” Dr. Schneider said. “The only way to fight that is to get early morning bright light exposure. That disappears more and more in the winter months, which is why we see conditions such as seasonal affective disorder.”
“Whenever we are awake when it’s dark outside, it causes changes in our circadian rhythms, particularly cortisol levels. Too much light at night disrupts our melatonin rhythms,” Dr. Malow said. “This leads to sleep loss, obviously in the summer when it’s light too late in the day and you’re not able to release melatonin, but perhaps more profoundly in the winter, such as when we shift to DST in March and it’s still dark in the morning. Waking up in the darkness is not healthy. We need that light to re-set our circadian rhythms. Dysregulation of cortisol and melatonin contributes to stress, altered metabolism, and inflammation.”
The Social Jetlag Phenomenon
It’s difficult to model what the long-term effects of such a permanent circadian misalignment might be, but one analogy can be found in the literature on time zone border effects.
“If you’re on the western edge of a time zone, you can be just a few miles away from the next time zone,” Dr. Malow explained. “Research has found profound differences in mortality, heart disease, obesity, and other health effects depending on whether you’re on the eastern or the western edge of a time zone.”
For example, a 2019 study in the Journal of Health Economics found that individuals on the “late sunset” side of a time zone boundary (western Michigan, for example) are more likely to be sleep deprived, more likely to sleep less than six hours, and less likely to sleep at least eight hours than those further east in their time zone. People are also more likely to be forced to wake up earlier on work and school days than free days, often resulting in less overall sleep (referred to as “social jetlag”).
“We also find evidence of significant discontinuities in the incidence of obesity, diabetes, cardiovascular diseases, and breast cancer. Summarizing these outcomes with a standardized composite health index, we find that living on the late sunset side of the border decreases the index by 0.3 standard deviations,” the authors noted. “These effects are the consequences of a long-term-exposure to circadian rhythms disruptions.”
These findings align with those reported in a 2017 study in the journal Cancer Epidemiology, Biomarkers, & Prevention, which found cancers including chronic lymphocytic leukemia in men and women; cancers of the stomach, liver, prostate, and non-Hodgkin lymphoma in men; and cancers of the esophagus, colorectum, lung, breast, and uterus in women all show an increased risk from east to west within a time zone.
The authors of the paper in the Journal of Health Economics also pointed out that, as would be expected, the health effects are larger among individuals with early working schedules and among those with school-aged children. Permanent DST could also be particularly detrimental to adolescents and teens, who already are very inclined to stay up later at night based on their natural biological rhythms.
“Teenagers fall asleep later and want to wake up later. It’s physiologically what they’re supposed to do,” said Dr. Schneider, noting that many school districts are moving toward later school start times, particularly in middle school and high school, to better match these natural cycles. “But if you counteract that with year-round DST, you’ll continue to force kids to wake up at physiologically suboptimal times, you will curtail the quality, timing, and duration of sleep they get.”
Previous attempts to move to permanent DST have had such negative results that they were quickly abandoned. At the height of the energy crisis, Congress voted on Dec. 14, 1973, to put the US on DST for two years, and President Nixon signed the bill the next day. On Jan. 7, 1974, the sun rose around 8:27 a.m. in most East Coast cities and towns. Newspapers featured photos of children getting off school buses in pitch blackness, carrying flashlights. A flurry of traffic accidents followed, some of them fatal, and shortly after Nixon resigned, Congress passed a bill to end the permanent DST experiment. It was signed by President Ford, and the country went back to “spring forward, fall back” in October 1974. (It could have been worse: Pentagon geographer Paul Mullinax argued for putting the continental US on a single time zone from Atlantic to Pacific, saying, “The human being is a very adaptive animal. There is no reason we have to be a slave to the sun.”)
And a three-year experiment of living on permanent “summer time” in Russia, put in place by then-president Dmitry Medvedev in 2011, was called off in 2014 after three years of dissatisfaction with going to work and school in complete darkness part of the year.
“Dark mornings have a worse effect on people’s state of health than dark evenings,” the head of sleep medicine at the Federal Medical and Biological Agency, Aleksandr Kalinkin, told the TASS news agency.
“I understand the appeal of permanent DST to some people,” Dr. Schneider said. “Initially, I was in that camp. But after talking to experts in circadian medicine, who’ve looked at natural models like Arizona and Hawaii [both states which opted out of the Uniform Time Act of 1966 and remain on standard time year-round], and how health effects change in the gradient of a time zone, the evidence is very convincing. We shouldn’t always be waking up at a natural disadvantage to our body clocks.”
“While there are some legitimate arguments for permanent DST, the bulk of the evidence from a health standpoint strongly supports abolishing the transition back and forth between DST and standard time and adopting permanent standard time,” said Dr. Malow. “There’s virtually no question that this approach is better for our health.”