A study published in the Canadian Medical Association Journal examined the health implications of adopting permanent daylight saving time (pDST). The research, released on Monday, compared the effects of maintaining daylight saving time year-round with those of adopting permanent standard time (pST). The authors concluded that pST would likely offer greater health benefits than pDST.

The study highlighted that while pDST could extend evening daylight, potentially aiding commuting, recreation, and certain economic activities, it would also lengthen morning darkness. This shift could disrupt circadian rhythms, as human biology is tuned to natural sunlight patterns. Morning light plays a critical role in synchronizing the body's internal clock, whereas evening light tends to delay it, affecting sleep quality, mood, and productivity.

Circadian rhythms naturally span approximately 24.2 hours, making alignment with external light cues essential. The researchers noted that moving westward within a time zone often results in later sunrises and sunsets, which can reduce sleep duration. One study cited in the analysis found that residents in the western portions of U.S. time zones experienced about an hour less sleep per week, with an additional hour of sleep linked to a 5 percent increase in long-term earnings. Similar findings emerged from a German study, which observed reduced working hours among workers in western regions.

Educational outcomes also appeared to be affected. A Florida study referenced in the paper associated an extra hour of pre-school sunlight with improved math and reading scores, comparable to the benefits of smaller class sizes. The authors emphasized that eliminating seasonal clock changes might mitigate short-term transition harms but would not address the chronic health effects associated with pDST. They referenced recommendations from global sleep and chronobiology societies supporting permanent standard time.

The research noted that several countries, including Russia and Chile, have attempted and later abandoned permanent daylight saving time due to concerns over dark winter mornings, sleep disruption, and public dissatisfaction. The United States previously adopted pDST during World War II and again in 1973 as an energy conservation measure, both of which were later reversed.

Currently, the U.S. Senate passed legislation in 2022 to establish permanent daylight saving time, but the House did not act. A new House bill has since been introduced to advance the proposal, though Senate consideration remains pending. President Trump has publicly supported the measure, recently sharing the personal phone number of Senator Tom Cotton (R-AR), who opposes the bill on social media. Cotton cited historical precedents of adopting and later repealing pDST, arguing that the policy has been implemented before.

The Canadian researchers warned that if the U.S. adopts pDST, Canada may face pressure to align its timekeeping practices, potentially affecting cross-border coordination. They suggested that the short-term convenience of extended evening light might not justify the long-term health trade-offs, particularly given the availability of alternative solutions.

The study contributes to ongoing debates about timekeeping policies and their impact on public health, emphasizing the need for evidence-based approaches to legislative decisions involving circadian science.