Canadian Analysis: Permanent Daylight Saving Harms Sleep and Mental Health

“With the push to eliminate the twice yearly clock change, Permanent Daylight Savings Time has emerged as the favorite for most states and provinces,” writes longtime Slashdot reader kbahey, sharing the findings from a recent analysis published in the Canadian Medical Association Journal. “Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?” said University of British Columbia’s Professor Raymond Lam, lead author of the study. “The health evidence points to standard time, largely because morning light matters for our body clocks, sleep, and mood.” Professor Lam and colleagues examined the health consequences of the two possible permanent systems rather than the broader question of whether seasonal clock changes should be abolished. They concluded that the accumulated evidence favors permanent standard time, which keeps the clock more closely aligned with human circadian biology.

This distinction, according to the team, becomes particularly important during winter. Permanent daylight saving time would push sunrise an hour later. In cities such as Toronto, for example, the latest winter sunrise would occur at 8:51 a.m., compared with 7:51 a.m. under permanent standard time. In Calgary, the corresponding times would be 9:40 a.m. and 8:40 a.m. The extra hour of morning darkness could leave people traveling to work or school before sunrise, while shifting more daylight into the evening. The change could have consequences for sleep, mood, learning and productivity, particularly among people who already have difficulty sleeping or who must follow early schedules. The reason is rooted in the body’s internal clock.

“Our biological clocks need morning light to stay synchronized with the 24-hour day,” said Simon Fraser University’s Professor Ralph Mistlberger, co-author of the study. “Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest.” The analysis also highlights concerns about seasonal depression. […] By delaying natural morning light, permanent daylight saving time would act in the opposite direction, potentially weakening an important circadian signal.