Permanent winter time is better for your health

Many countries have stopped switching between summer and winter time and kept one of the two. Researchers at the University of British Columbia and Simon Fraser University in Canada assessed the health effects of both options: standard time (the usual winter time) and summer time, which puts the clock forward a full hour. The team reviewed published research on body clocks, sleep, mood, education and the economy, looked at countries that adopted permanent time, and compared sunrise and sunset in different Canadian cities. Their aim was to find out which time would be better for health if governments stopped changing the clocks twice a year. The work was published in the Canadian Medical Association Journal.

They found that keeping standard (winter) time all year is the healthier choice, because morning sunlight arrives earlier by the clock and helps our bodies set their sleep and waking times. To show the difference, the team took the example of Toronto. In early January, when winter sunrise is latest, the sun rises at 7:51 a.m. on permanent standard time and at 8:51 a.m. on permanent summer time. Work and school, however, keep the same hours. Someone who wakes up at seven sees daylight a full hour sooner on standard time.

The body struggles to adapt to winter sunrise. Every day it has to adjust its internal clock by about ten minutes to keep up with the late sunrise. With permanent summer time there would be less morning light, and this daily correction would be disrupted. Sleep gets shorter, and symptoms of depression and mental and physical exhaustion appear (winter depression). It is much harder for teenagers and young adults, whose body clocks run late. Some even argue that regions on permanent summer time lag behind economically and have more illness.

Although permanent winter time comes out ahead in this analysis, the question is not simple. Permanent summer time gives brighter evenings and may leave more time for outdoor activities and socialising, while winter time brings darkness earlier in the evening, and early summer sunrises may wake some people sooner than they would like. How much the choice matters also depends on a city's location and where it sits within its time zone. Some countries tried permanent summer time and then went back: the United States adopted it in 1974 and abandoned it the same year over worries about dark winter mornings and children going to school before sunrise, and Russia adopted it in 2011 and reversed it in 2014. In Canada, British Columbia moved to permanent summer time in March 2026, and Alberta and the Northwest Territories have also adopted summer time all year, dropping the November clock change. But the researchers stress that most of the evidence comes from observation and geographical comparisons, so we do not know all the long-term health effects of each option precisely. They recommend permanent winter time. If governments choose permanent summer time, they call for later school and work hours, more morning light exposure, and monitoring for any rise in sleep problems, winter depression, absence from work or school, and road injuries. In our own daily lives, we can make sure we get good light in the morning, especially if we wake before sunrise; the researchers note that bright indoor light in the morning can also help set our body clock.