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The annual switch to daylight saving time (DST) in many parts of the world is detrimental to public health and should be abolished in favor of permanent standard time (ST), Canadian researchers wrote in a recent editorial.

The policy of turning clocks forward by an hour in the spring causes “discrepancies between the circadian biological clock and the environmental light-dark cycle,” leading to “social jet lag,” noted lead author David Dongkyung Kim, MD, assistant professor of geriatric psychiatry at the University of Toronto, Toronto, and colleagues.

The Viewpoint was published on April 29 in JAMA.

Clear Evidence

“DST is a policy that affects the lives of millions of people, but the potential benefits do not seem to outweigh the potential harms to public health,” Kim told Medscape Medical News.

“Clear evidence in the medical literature as well as widespread expert consensus [shows] the acute transition of the clock time in the spring has been associated with increased myocardial infarction, ischemic stroke, and atrial fibrillation admissions,” he added. “But it is not only the sudden change in the clock that is the issue. ST is more aligned with our natural circadian rhythms, and chronic misalignment has been associated with many negative health effects.”

Canada first initiated DST during World War I. The rationale was to add more light to waking hours, thus saving energy. Today, only Saskatchewan and Yukon have abolished the time change, staying on permanent ST. Ontario passed legislation in 2020 to change to permanent DST, but it was contingent on Quebec and New York doing likewise, said Kim.

“Many studies seem to show an acute worsening of health with the spring transition, but not the fall transition, suggesting the health issues are due not only to acute changes in clock time but also to the discrepancy between clock time and circadian rhythm,” the authors noted. “Although many studies suggest increased traffic crashes due to DST transition, others do not show this connection,” they added. And findings on DST transition and mental health risks such as unipolar depression, manic episodes, and suicide are also mixed.

“The main argument I hear for establishing permanent DST is that it is nicer to see the sun set later in the day,” said Kim. “To that, I respond that you can use your own volition to wake up an hour earlier without forcing permanent DST on the entire population.”

Late evening light, which DST makes possible, disrupts the natural seasonal adjustment of circadian rhythms. The misalignment between one’s personal schedule and the circadian rhythm, which is called social jet lag, is well understood. It is associated with negative outcomes such as obesity, heart disease, metabolic syndrome, and depression.

Global Consensus

In a position statement, the Canadian Sleep Society called for abandoning DST, and there is “global consensus from sleep and chronobiology experts on this matter,” said Rébecca Robillard, PhD, a clinical neuropsychologist and associate professor of psychology at the University of Ottawa, Ottawa. Robillard, who did not contribute to the editorial, also leads clinical sleep research at the University of Ottawa Institute of Mental Health Research at the Royal Ottawa Mental Health Centre and is co-chair of the Canadian Sleep Research Consortium.

“Considering the impacts that this practice has on a large range of health and safety issues, we should abolish DST and stick to ST all year around,” she told Medscape Medical News. “Time change goes beyond gaining or losing an hour of sleep; it perturbs our biological clock, which results in population-wide increases in heart attacks, strokes, infections and immune diseases, digestive problems, pregnancy and childbirth complications, and a deterioration in mental health. It’s not a question of opinion or personal preference, but of public health and scientific evidence.”

Kim and Robillard reported having no relevant financial relationships.

Kate Johnson is a Montreal-based freelance medical journalist who has been writing for more than 30 years about all areas of medicine.