The Social Clock Changed. The Sun and Biologic Clock Did Not. - The Consequences

Alberta has stopped changing its clocks. Good. There are strong arguments for getting rid of the twice-a-year disruption. But once we decided to stop changing the clocks, we still had to decide which time to keep. Alberta chose permanent Daylihgt Saving Time (DST), now called Alberta Time, fixed at UTC−6. That puts our clocks permanently one hour ahead of Mountain Standard Time. The Sun, of course, did not move with us. It will rise when the rotation of the Earth says it will rise. All we changed is what the clock on the wall says when that happens. In practical terms, we have moved an hour of sunlight out of our winter mornings and into the evening. There are benefits. Longer evening light is wonderful for recreation. Some people prefer driving home in daylight. Businesses may benefit and nobody has to change a clock twice a year. But we did not gain a minute of sunlight. We simply decided when we wanted it. The October 2026 analysis in the Canadian Medical Association Journal looked specifically at the Canadian evidence and concluded that the balance of health evidence favours permanent Standard Time, not permanent DST. The Canadian Sleep Society, American Academy of Sleep Medicine and other circadian experts have reached the same broad conclusion. Permanent DST gives us less light after waking and more light later in the evening. Morning light tends to shift our Biological Clock earlier. Evening light tends to shift it later. We have chosen to move both in the opposite direction.

There are three clocks worth thinking about. First is the Sun Clock, the natural light-dark cycle created by the rotation of the Earth. Then there is our Biological Clock, with a master circadian pacemaker in the brain helping coordinate rhythms throughout the body. Finally, there is our Social Clock, the one on the wall. That is the clock we control or not, depending on if you are the decision-maker or the decision-taker. It decides when the alarm rings, when the bus comes, when breakfast is eaten, when work begins and when a teacher asks a Grade 8 student to solve a mathematics problem. Standard time does not mean that the Sun is directly overhead at exactly noon everywhere. Geography is not that tidy. It does keep social time closer to solar time than DST does. Our Biological Clock did not evolve according to the clock on the wall. Our Biologic Clock is hand-in-glove connected to the rising sun! Light reaching specialized cells in our eyes is the dominant environmental signal our brain uses to keep biological time aligned with the 24-hour day. Our brain clock is also not working alone. There are circadian clocks in the essential organs and body systems: our brain, liver, skeletal muscle, pancreas, fat tissue, gastrointestinal system and other tissues. Food, activity, how we metabolize it and manage it, all depend on sleep and especially daily sunlight to provide timing reset to optimize health over disease in regulating these systems as well. Our biology coordinates many rhythms at once. When the time we wake, eat, work and sleep moves away from our biological time, and that disruption of the Biological Clock is because of a forced disconnect with the Sun Clock by tinkering with the Social Clock , that disconnect has defined troubling long-term health consequences. Researchers describe this in different circumstances as circadian misalignment or social jet lag. We can move the clock on the wall in a few seconds. Our biology still takes its timing from the Sun, not the Wall clock. Morning light does much more than help us see. Specialized cells in the eyes send information about environmental light to the brain's circadian and alerting systems. Morning light helps tell the brain that the biological day has begun. It helps set our circadian clock and also has immediate effects on alertness. There is another interesting part of waking that is relevant here. Cortisol normally rises rapidly during the first 30 to 45 minutes after awakening. This is called the cortisol awakening response and it helps prepare the body for the demands of the coming day. Controlled experiments show that bright light (especially the sunrise) after awakening increases this response compared with dim light. That does not mean cortisol fails to rise when we wake in darkness or that our body remains asleep until sunlight hits our eyes, but our brain remains partially intoxicated by the lack of light, not perky and ready but "lights on but is there somebody home". Our internal clock is already preparing us to wake before we open our eyes. But morning light adds another powerful signal. Reviews of experimental studies also show that brighter daytime light generally increases alertness, although the evidence for more complex cognitive performance is less consistent. So I am not going to tell you that sunlight makes children smarter. The research does not show that. What it does show is that morning light helps establish an awake, alert, learning ready and appropriately timed brain. Alberta has now delayed that natural signal by an hour on the clock. And where do you find that brain, sitting in the classroom? As Apollo 13 famously said (paraphrased): "We got a problem Houston."

Now think about 9:00 a.m. Every school morning we ask nearly three-quarters of a million developing brains in Alberta to pay attention, to regulate behaviour, to ignore distractions, to remember yesterday, to process something new, to reason, to solve problems... all the things of learning and learning readiness. But at the same time, we ask teachers to create the conditions that make all of this possible. Under permanent DST, morning sunlight arrives an hour later by the clock and evening sunlight stays an hour later. IMPORTANT: Adolescents are especially concerning because puberty already shifts their biological clocks later. Their bodies naturally become inclined toward later sleeping and waking, while school still starts early. Permanent DST pushes the light-dark schedule another hour in that same direction. Experimental sleep restriction in adolescents produces more sleepiness and inattention and poorer learning. Then there is a remarkable natural experiment from Florida that was highlighted in the new CMAJ analysis. Students receiving an additional hour of sunlight before school had mathematics scores about 0.08 standard deviations higher and reading scores about 0.06 standard deviations higher. The largest differences occurred around puberty. That does not mean an extra hour of sunlight automatically raises everyone's marks. It does tell us that the timing of sunlight relative to school deserves our attention. We also have the much larger school-start literature. A meta-analysis of 28 studies involving approximately 1.77 million young people found that later school starts were associated with longer sleep, less negative mood and better overall developmental outcomes. Starts between 8:30 and 8:59 generally produced better outcomes than starts between 8:00 and 8:29. We spend enormous amounts of time trying to improve what happens after students sit down at their desks. Their biological readiness to learn begins before they get there.

And do not forget the teachers. Their brains and bodies are living under the same shifted clock. They wake in the same darkness and travel to school under the same morning conditions. Then they walk into a classroom and are expected to bring attention, enthusiasm, judgement, patience and emotional regulation to a room full of children. Sleep is already an issue in this profession. A review of 33 studies from 15 countries found substantial insomnia symptoms among teachers, although the studies were too different to use those numbers as an estimate for Alberta teachers. More interesting is what happened when researchers followed teachers after a large school district delayed secondary-school start times. High-school teachers woke 28 minutes later, slept 22 minutes longer and reported better daytime functioning. Teacher sleep may also affect what happens in the classroom. A smaller study following 17 teachers and 437 students over ten school days found that poorer teacher sleep was related to greater teacher stress and emotional transmission into the classroom, which in turn was related to students' classroom satisfaction and academic motivation. It was a small observational study, so we should not make too much of it. But the basic point is important. Teaching is demanding interpersonal work. At 9:00 a.m. we are not only asking a child to be ready to learn. We are asking a teacher who awoke under the same shifted clock to get an entire room of children alert, attentive, emotionally regulated and ready to learn. That matters.

Then there is metabolism. This is an area where it is very easy to make the story sound simpler than it actually is. Waking before sunrise does not mean our metabolism remains asleep. The body does not wait for sunlight before beginning the transition to wakefulness. Cortisol, body temperature, glucose regulation, autonomic activity and many other processes have circadian rhythms and are already changing before and around awakening. Nor is there evidence that breakfast eaten before sunrise is automatically directed toward fat storage. What we do know is that metabolism is organized in time. Glucose tolerance changes across the biological day. The liver, muscle, pancreas and fat tissue all participate in circadian regulation. Sleep, eating, activity and light all provide timing information. Controlled human experiments have deliberately moved behavioural time away from biological time to see what happens. The results are important. In healthy adults, post-meal glucose was 17% higher in the biological evening than in the biological morning, independent of the behavioural schedule. Circadian misalignment itself increased post-meal glucose by about 6%, with evidence of reduced insulin sensitivity. Similar effects have been demonstrated in chronic shift workers. An earlier experiment moved participants' eating and sleeping schedules approximately 12 hours out of phase. Leptin fell 17%, glucose increased despite higher insulin, blood pressure increased and sleep efficiency deteriorated. Most strikingly, three of eight participants with sufficient data developed post-meal glucose responses in the range normally seen in a prediabetic state during the experiment. That was an extreme laboratory experiment. It was nothing like moving Alberta's clock by one hour and we should not pretend that it was. What it demonstrates is that human metabolism is sensitive to when we sleep, wake and eat relative to our biological time. This is why I am less concerned about one dark breakfast than I am about what happens when small circadian disruptions are repeated for months and years. A systematic review and meta-analysis of 68 studies examining social jet lag found associations with higher BMI, greater waist circumference, higher systolic blood pressure and higher HbA1c in the better-quality studies. It did not establish a higher prevalence of type 2 diabetes or metabolic syndrome, and the studies varied considerably. Another meta-analysis brought together 43 studies and 231,648 people and found social jet lag associated with BMI, fat mass, body-fat percentage, waist circumference and overweight or obesity. Research in children and adolescents points in a similar direction, with greater variability in sleep timing and social jet lag associated with higher measures of adiposity. These are mostly observational studies. They do not prove that moving a clock causes obesity or diabetes. But sleep duration, sleep regularity and circadian alignment are increasingly recognized as part of cardiometabolic health. That should matter in a province already dealing with obesity, prediabetes, diabetes and cardiovascular disease. Moving a population-level environmental timing signal away from morning light is not something I think we should treat as biologically irrelevant.

Geography has also given us a useful natural experiment. People living toward the western edge of a time zone experience sunrise and sunset later by the clock than people living farther east, even though school and work schedules generally follow the same Social Clock . Researchers used the sharp change in solar timing at U.S. time-zone boundaries to examine what happens. People exposed to an additional hour of natural evening light slept, on average, about 19 minutes less each night and were more likely to report insufficient sleep. Differences were also found in obesity, diabetes, cardiovascular disease and other health outcomes. Those disease findings are observational, so they cannot tell us that later sunlight caused the disease. The sleep result is especially interesting because it tells us that people do not simply compensate perfectly when sunlight moves later relative to work and school schedules. Nineteen minutes does not sound like much. But nineteen minutes repeated night after night becomes hours of lost sleep. And remember, that is a population average. Alberta has now moved everyone one social-clock hour toward a later solar schedule without moving anyone's house west. I am not saying Albertans will therefore lose 19 minutes of sleep. We do not know that. But we already have evidence that later solar time relative to fixed social schedules is associated with less sleep. That should at least make us curious about what happens here.

There is also a mental-health question, particularly in a northern country where winter daylight is already limited. Morning bright-light therapy is an established treatment for seasonal affective disorder because appropriately timed light affects circadian timing and mood. The new Canadian analysis discusses seasonal depression and the much larger number of people who experience milder seasonal changes in sleep, energy, appetite and mood. There is also some fascinating new research from Australia. In 2026, researchers studying the Australian Genetics of Depression Study identified what they describe as a possible circadian subtype of depression. About 23% of their depression sample met the proposed criteria, which included features such as social jet lag, seasonal symptoms, delayed sleep timing, evening chronotype, morning tiredness and excessive sleep. This group also showed genetic associations involving later sleep timing as well as BMI, triglycerides, inflammation and insulin resistance. This is new research and the authors are clear that it needs to be replicated. It does not mean that circadian disruption causes one quarter of depression. But it adds to something we are beginning to understand much better: circadian biology is connected to sleep, brain function, mood and metabolism. These systems do not live in separate boxes.

We have also tried permanent DST before. Britain kept clocks one hour ahead through the winters from 1968 to 1971 and eventually returned to seasonal time. The United States introduced year-round DST during the 1970s energy crisis and abandoned it after one winter rather than completing the planned experiment. Russia moved to permanent DST in 2011 and switched away from it three years later. These were different countries, different circumstances and different reasons for changing course. They are not experiments proving that permanent DST damages health. But the same practical complaint appeared repeatedly: winter mornings were simply too dark. That problem becomes more obvious the farther north you go. Alberta already has late winter sunrises. Permanent DST adds another hour to the clock before that sunrise arrives. We are therefore not the first place to decide that evening light sounds attractive. We should probably pay attention to what happened when other populations actually lived through the winter mornings that came with it.

So where does all of this leave us? There are things we know very well and things we do not. We know that light is the major environmental signal setting our circadian clock. We know morning light has immediate alerting effects. We know bright light after waking affects the normal cortisol awakening response. We know adolescents naturally shift toward later biological timing and that insufficient sleep makes them sleepier, less attentive and poorer learners. We know later school starts increase sleep. We know teachers themselves sleep longer and report better daytime functioning when secondary schools start later. We know circadian misalignment can impair glucose tolerance and insulin sensitivity in controlled human experiments. We know social jet lag is associated with several measures of adiposity and cardiometabolic risk. We know people living with later solar timing within a time zone tend to sleep less. What we do not know is whether permanent DST will cause Alberta students to perform worse academically or increase rates of obesity, diabetes, cardiovascular disease or depression. But a profound body of evidence points to this as an unfortunate outcome. Those would be claims beyond the evidence. But there is more than enough evidence to ask why we would deliberately move morning sunlight later for an entire population and then assume nothing important will change.

At 9:00 tomorrow morning, a teacher somewhere in Alberta will stand in front of a classroom and try to make something extraordinary happen inside 25 young brains. Get their attention. Settle the room. Spark some curiosity. Ask them to remember yesterday. Introduce something they have never understood before. Notice the student who is drifting away. Help another regulate an emotion. Somehow turn all of that into learning. We spend enormous amounts of money trying to improve what happens during those hours, yet learning readiness begins before the lesson plan does. We spend equally enormous resources addressing obesity, prediabetes, diabetes, cardiovascular disease and mental health while increasingly recognizing sleep and circadian health as part of prevention. Alberta has now changed something relevant to both. So let's measure what happens. Look at student sleep, morning sleepiness, attendance, tardiness, behavioural incidents by time of day, teacher absenteeism and daytime functioning. Look at first-period learning compared with later periods if the data allow it. Look at morning pedestrian and traffic injuries. And perhaps we should finally have a serious conversation about school start times. If we are going to move sunrise an hour later by the clock, it seems reasonable to ask whether the school bell should stay exactly where it was. We gained no sunlight. We simply moved it away from the part of the day when hundreds of thousands of developing brains and their teachers are being asked to do some of their most important work. What did we gain in the evening, and what have we lost every morning?

References

Permanent DST

Lam, R. W., Mistlberger, R. E., Baylis, P., & Choi, A. (2026). Analysis of health impacts associated with adopting permanent standard time or permanent DST to inform policy in Canada. CMAJ, 198, E1335–E1340. https://doi.org/10.1503/cmaj.261089

Why it matters: This is the most important policy reference for the article. Published in October 2026, it specifically considers the Canadian context and concludes that the preponderance of health evidence supports permanent standard time rather than permanent DST. It addresses circadian alignment, morning light, sleep, mental health, learning and productivity, and recommends monitoring outcomes such as sleep, school absenteeism and lateness where permanent DST is adopted.

Rishi, M. A., Cheng, J. Y., et. al., (2024). Permanent standard time is the optimal choice for health and safety: An American Academy of Sleep Medicine position statement. Journal of Clinical Sleep Medicine, 20(1), 121–125. https://doi.org/10.5664/jcsm.10898

Why it matters: Authoritative professional-society statement supporting permanent standard time. Particularly useful for explaining why morning light and evening darkness better align with human circadian biology. It also identifies adolescents and young adults as particularly susceptible to circadian misalignment.

Malow, B. A. (2022). It is time to abolish the clock change and adopt permanent standard time in the United States: A Sleep Research Society position statement. Sleep, 45(12), zsac236. https://doi.org/10.1093/sleep/zsac236

Why it matters: Independent position statement from the Sleep Research Society. Supports eliminating seasonal clock changes while specifically favouring permanent standard time rather than permanent DST. Useful because it separates the two questions: ending clock changes and deciding which time should become permanent.

Morning Light, Alertness and the Biological Clock

Souman, J. L., Tinga, A. M., te Pas, S. F., van Ee, R., & Vlaskamp, B. N. S. (2018). Acute alerting effects of light: A systematic literature review. Behavioural Brain Research, 337, 228–239. https://doi.org/10.1016/j.bbr.2017.09.016

Why it matters: Systematic review of 68 experimental studies examining the immediate alerting effects of light. Strong support for the statement that light does more than reset circadian timing over subsequent hours and days. It can have acute effects on alertness while a person is exposed to it.
Important limitation: This does not establish that sunlight makes students more intelligent or directly improves every form of cognitive performance.

Siraji, M. A., Kalavally, V., Schaefer, A., & Haque, S. (2022). Effects of daytime electric light exposure on human alertness and higher cognitive functions: A systematic review. Frontiers in Psychology, 12, 765750. https://doi.org/10.3389/fpsyg.2021.765750

Why it matters: Systematic review of 59 quantitative studies. Brighter daytime light and light with stronger short-wavelength components generally increased alertness. Effects on higher-order cognition were less consistent. This supports the careful wording in the article: morning light contributes to an alert brain, but we should not claim that sunlight simply makes children smarter.

Flo-Groeneboom, E., et al. (2024). Acute effects of light during daytime on central aspects of attention and affect: A systematic review. Biological Psychology, 192, 108845. https://doi.org/10.1016/j.biopsycho.2024.108845

Why it matters: More recent systematic review examining daytime light, attention and affect. Alertness and some aspects of working memory showed the clearest responses, while evidence for sustained attention and executive functioning was less consistent. Adds contemporary support to the alerting-light argument while reinforcing the need not to exaggerate cognitive effects.

Petrowski, K., et al. (2019). The effects of post-awakening light exposure on the cortisol awakening response in healthy male individuals. Psychoneuroendocrinology. PMID 31220690.

Why it matters: Controlled experimental evidence that bright light after awakening can amplify the cortisol awakening response compared with dim light. Supports the discussion of light contributing to the normal physiological transition into the active part of the day.
Important limitation: This does not mean cortisol fails to rise in darkness, that sunlight is required to “switch on” metabolism, or that the body remains metabolically asleep until sunrise. The endogenous circadian system already anticipates awakening.

Adolescents, Sleep and Learning

Yip, T., Wang, Y., Xie, M., Ip, P. S., Fowle, J., & Buckhalt, J. (2022). School start times, sleep, and youth outcomes: A meta-analysis. Pediatrics, 149(6), e2021054068. https://doi.org/10.1542/peds.2021-054068

Why it matters: Major meta-analysis involving 28 studies and approximately 1.77 million young people. Later school start times were associated with longer sleep, less negative mood and better overall developmental outcomes. Start times between 8:30 and 8:59 a.m. generally showed better outcomes than starts between 8:00 and 8:29 a.m.
Why it matters for Alberta: If permanent DST shifts natural morning light later while school schedules remain unchanged, school start time becomes an obvious part of the policy discussion.

Beebe, D. W., Field, J., Miller, M. M., Miller, L. E., & LeBlond, E. (2017). Impact of multi-night experimentally induced short sleep on adolescent performance in a simulated classroom. Sleep, 40(2), zsw035.

Why it matters: Particularly strong evidence because sleep was experimentally manipulated rather than simply observed. Eighty-seven adolescents aged 14–16 experienced five nights of restricted versus healthy sleep opportunity in a randomized crossover design. Restricted sleep produced greater observable sleepiness and inattention and poorer educational quiz performance.
Why it matters for the article: This directly supports the statement that inadequate adolescent sleep changes what arrives in the classroom before teaching begins.

Solar Timing and Academic Performance

Gibson, M., & Shrader, J. (2018). Time use and labor productivity: The returns to sleep. Review of Economics and Statistics, 100(5), 783–798.

Why it matters: Uses geographic variation in solar timing to examine sleep and productivity. The broader body of time-zone-boundary research is important because geography creates naturally occurring differences in the relationship between solar time and social time.
Important note: The specific Florida student findings discussed in the article, approximately 0.08 SD higher mathematics scores and 0.06 SD higher reading scores associated with an additional hour of sunlight before school, are summarized in Lam et al. (2026). The CMAJ paper should therefore remain the primary citation for those exact figures unless the original educational study is cited directly.

Teachers, Sleep and Classroom Functioning

Gierc, M., Jackowich, R. A., Halliday, S., & Davidson, J. R. (2023). A scoping study of insomnia symptoms in school teachers. Behavioral Sleep Medicine, 21(3), 304–321. https://doi.org/10.1080/15402002.2022.2087655

Why it matters: This scoping review searched six major databases and identified 33 relevant studies from 15 countries examining insomnia symptoms among kindergarten to Grade 12 teachers. Among studies that met the review's validity and reliability criteria, 36%–61% of teachers reported insomnia symptoms. Factors associated with insomnia symptoms included classroom violence, low job satisfaction, pain, depression and rumination.
Why it matters to this article: It establishes that sleep health is already an important issue in the teaching profession. That matters when considering a population-wide change in the timing of morning light. Teachers are not simply responsible for managing the consequences of tired students. Their own sleep, alertness and daytime functioning matter too.
Important limitation: The authors describe the teacher insomnia literature as heterogeneous and generally low quality with respect to measurement. The 36%–61% range refers to insomnia symptoms, not necessarily diagnosed insomnia, and should not be presented as the prevalence of insomnia among Alberta teachers.

Wahlstrom, K. L., Plog, A. E., McNally, J., & Meltzer, L. J. (2023). Impact of changing school start times on teacher sleep health and daytime functioning. Journal of School Health, 93(2), 128–134. https://doi.org/10.1111/josh.13254

Why it matters: This is much stronger than I made clear in the previous reference list. Teachers in a large suburban school district completed surveys before and after school start times changed and again at follow-up. Sample sizes were large: 1,687 teachers before the change, 1,857 after the change and 1,812 at follow-up. After secondary schools started later, high-school teachers woke up 28 minutes later, slept 22 minutes longer and reported improved daytime functioning. Middle-school teachers woke 14 minutes later and slept 13 minutes longer, although their improvements in daytime functioning were not statistically significant.
Why it matters to this article: This provides direct evidence that school timing affects teachers, not only students. That is the important connection. If we are discussing morning circadian timing, learning readiness and whether school schedules fit human biology, the adults standing in front of the classroom belong in that discussion. When high-school start times moved later, teachers gained measurable sleep and their daytime functioning improved.
Important limitation: This study examined changing school start times, not permanent DST or morning sunlight. It therefore supports our argument that teacher sleep and functioning respond to school timing. It does not establish that Alberta's permanent DST will reduce teacher sleep by a particular amount.

Poon, C. Y.-S., Hui, V. K.-Y., Yuen, G. W.-C., Kwong, V. W.-Y., & Chan, C. S. (2019). A well-slept teacher is a better teacher: A multi-respondent experience-sampling study on sleep, stress, and emotional transmission in the classroom. PsyCh Journal, 8(3), 280–292. https://doi.org/10.1002/pchj.282

Why it matters: This experience-sampling study followed 17 high-school teachers and 437 students from two Hong Kong high schools across 10 school days. Poorer teacher sleep quality was associated with teacher stress. Teacher stress was associated with greater nervousness and irritability, and teacher nervousness was subsequently associated with greater nervousness and irritability among students. Student irritability was negatively associated with academic motivation, and these emotional pathways were associated with lower in-class satisfaction.
Why it matters to this article: This gives us evidence for the idea that teacher sleep does not necessarily stop with the teacher. A teacher's sleep, stress and emotional state are part of the social environment of the classroom. That makes teacher sleep relevant when we ask what conditions help an entire classroom become attentive, regulated and ready to learn.
Important limitation: This was a small observational study involving only 17 teachers in two Hong Kong high schools. It demonstrates associations and a plausible emotional pathway. It does not prove that poor teacher sleep causes poorer student learning, nor does it tell us what permanent DST will do to Alberta teachers.

Circadian Misalignment, Glucose and Insulin Sensitivity

Morris, C. J., Yang, J. N., Garcia, J. I., Myers, S., Bozzi, I., Wang, W., Buxton, O. M., Shea, S. A., & Scheer, F. A. J. L. (2015). Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans. Proceedings of the National Academy of Sciences of the United States of America, 112(17), E2225–E2234. https://doi.org/10.1073/pnas.1418955112

Why it matters: One of the strongest mechanistic studies supporting the metabolic section. Under controlled laboratory conditions, glucose tolerance was worse in the biological evening than biological morning. Circadian misalignment independently increased post-meal glucose by approximately 6%, with the insulin response indicating reduced insulin sensitivity.
What it establishes: Glucose regulation depends partly on biological timing, not simply what or how much someone eats.
What it does not establish: A one-hour permanent DST shift will produce a 6% increase in glucose in Albertans.

Scheer, F. A. J. L., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences of the United States of America, 106(11), 4453–4458. https://doi.org/10.1073/pnas.0808180106

Why it matters: Landmark controlled human experiment. Circadian misalignment decreased leptin, increased glucose despite increased insulin, increased mean arterial pressure and reduced sleep efficiency. Most strikingly, three of eight participants with sufficient data produced post-meal glucose responses in the range typically observed in a prediabetic state during the misalignment condition.
Critical limitation: The experimental disruption was severe, approximately a 12-hour behavioural/circadian displacement. It should never be equated directly with Alberta's one-hour clock shift. Its importance is mechanistic: substantial circadian misalignment can directly alter human metabolic physiology.

Wefers, J., van Moorsel, D., Hansen, J., Connell, N. J., Havekes, B., Hoeks, J., van Marken Lichtenbelt, W. D., Duez, H., Phielix, E., Kalsbeek, A., & Schrauwen, P. (2018). Circadian misalignment induces fatty acid metabolism gene profiles and compromises insulin sensitivity in human skeletal muscle. Proceedings of the National Academy of Sciences of the United States of America, 115(30), 7789–7794.

Why it matters: Controlled human evidence that short-term circadian misalignment reduces skeletal-muscle insulin sensitivity and changes metabolic gene expression. Strengthens the biological mechanism behind the glucose findings.

Social Jet Lag and Cardiometabolic Health

Bouman, E. J., Beulens, J. W. J., Groeneveld, L., de Kruijk, R. S., Schoonmade, L. J., Remmelzwaal, S., Elders, P. J. M., & Rutters, F. (2023). The association between social jetlag and parameters of metabolic syndrome and type 2 diabetes: A systematic review and meta-analysis. Journal of Sleep Research, 32(3), e13770. https://doi.org/10.1111/jsr.13770

Why it matters: This is still an important review because it examined a broad range of metabolic outcomes rather than obesity alone. Sixty-eight studies were included, of which 38 were rated high quality, 27 moderate and three low quality. Among the high-quality studies, social jet lag was associated with a BMI approximately 0.49 kg/m² higher and a waist circumference approximately 1.11 cm greater. There were also statistically significant associations with slightly higher systolic blood pressure and higher HbA1c. The waist-circumference result is probably the most convincing of these associations because heterogeneity was considerably lower than for BMI, blood pressure or HbA1c.
Why it matters to this article: This study supports a cautious statement that repeated differences between biological and social timing are associated with some cardiometabolic risk markers. It helps connect circadian health with the broader discussion of obesity and metabolic health, but it should be supporting evidence rather than the centre of our causal argument.
Important limitation: This evidence is weak. Sixty-three of the 68 studies were cross-sectional, and the authors rated the overall certainty of evidence as low. Heterogeneity was extremely high for several outcomes. Importantly, the meta-analysis found no statistically significant association with fasting glucose, HOMA-IR, prevalent type 2 diabetes or prevalent metabolic syndrome. But observational studies weaknesses in identifying clear outcomes or causation. So iot is understandable that this paper should not be used to say that social jet lag causes diabetes or insulin resistance. Our controlled circadian-misalignment experiments are much stronger evidence for the biological mechanism (See later).

Arab, A., Karimi, E., Garaulet, M., & Scheer, F. A. J. L. (2024). Social jetlag and obesity: A systematic review and meta-analysis. Obesity Reviews, 25(3), e13664. https://doi.org/10.1111/obr.13664

Why it matters: This meta-analysis included 43 studies involving 231,648 participants and examined adiposity specifically. Social jet lag was positively associated with BMI, fat mass, fat-mass index, percentage body fat and waist circumference. The pooled odds of overweight/obesity were also higher among people with greater social jet lag. This is useful because several different measures of adiposity pointed in the same general direction rather than the finding depending entirely on BMI.
Why it matters to this article: It supports the statement that habitual differences between social and biological timing are associated with adiposity across large populations. Combined with controlled experimental evidence showing that circadian misalignment can impair glucose regulation and insulin sensitivity, it gives us a reasonable basis for treating circadian timing as one part of the much larger obesity and metabolic-health picture.
Limitation: This remains predominantly observational evidence. Of the 43 included studies, 36 were cross-sectional, six longitudinal and one case-control. Heterogeneity was also very high for several outcomes, including BMI, percentage body fat, waist circumference and overweight/obesity. The association with BMI, for example, was statistically significant but modest. This paper therefore supports an association with adiposity, not the claim that social jet lag causes obesity.

Zhou, J., Chen, H., Deng, W., Xiong, J., Zhang, J., & Zhang, H. (2026). Associations of weekday-to-weekend and day-to-day sleep differences with adiposity-related measures in children and adolescents: A systematic review and meta-analysis. Nutrition, Metabolism and Cardiovascular Diseases, 36(3), 104420. https://doi.org/10.1016/j.numecd.2025.104420

Why it matters: This reference matters because it is particularly relevant to children and adolescents. The meta-analysis included 37 studies and 197,873 children and adolescents. In the initial pooled analysis, those with the greatest social jet lag had a slightly higher BMI-z score, greater percentage fat mass and approximately 25% higher odds of overweight/obesity compared with those with the least social jet lag. Greater weekday-to-weekend differences in bedtime and other measures of sleep variability were also associated with some adiposity outcomes.
Why it matters to this article: It tells us that irregular sleep timing and social jet lag deserve attention in young people rather than treating circadian health as an adult issue. That is relevant when we are discussing adolescents whose circadian timing is already shifting later during puberty.
Limitations: When the researchers used a model that incorporated study quality, the associations between social jet lag and BMI-z, percentage fat mass and overweight/obesity became statistically nonsignificant. The evidence is observational and does not establish that social jet lag causes childhood obesity or it does not. This paper shows a concerning pattern, but it also shows that the youth evidence is not yet as robust as the adult adiposity meta-analysis. The limitations is that the students were not followed long enough to identify the longer term life health outcomes of the social jet lag consequences.

Lin, M.-Y., Kang, Y.-N., Apriliyasari, R. W., & Tsai, P.-S. (2024). Association between social jetlag and components of metabolic syndrome: A systematic review and meta-analysis. Journal of Nursing Research, 32(5), e354. https://doi.org/10.1097/jnr.0000000000000628

Why it matters: This newer review provides an interesting counterpoint to Bouman. It included 16 studies of adults and reported that social jet lag of two hours or more, compared with less than one hour, was associated with greater odds of metabolic syndrome (pooled OR = 1.52). Greater social jet lag was also associated with greater waist circumference.
Importance to this article: It shows that evidence published after the Bouman search continues to raise concern about metabolic health and circadian misalignment. Its metabolic-syndrome finding makes it useful when assessing how the evidence is developing rather than simply selecting studies that support our argument.
Important limitation: Although 16 studies were included in the systematic review, the individual meta-analyses contained only two or three studies for each outcome. That is a thin evidence base. It is useful supplementary evidence, but Bouman's (the first paper in this section) included a much larger review and remains the better anchor for the observational metabolic literature.

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What These Studies Actually Say…

The evidence supports saying that social jet lag is associated with several measures of adiposity and some cardiometabolic risk markers, particularly BMI and waist circumference. The adult adiposity evidence is reasonably consistent in direction, although much of it is cross-sectional and several pooled estimates have very high heterogeneity. But one can not explicitly claim that Alberta's one-hour shift to permanent DST will absolutely cause obesity, prediabetes or diabetes. But there are strong signals pointing in this direction. The strongest metabolic argument comes from lining up the observational reviews beside the controlled human experiments that clearly show that experimentally imposed circadian misalignment ("imposed" kind-of-what is happening in Alberta) can impair glucose tolerance and insulin sensitivity. These controlled human experiments establish biological plausibility and direct physiological effects under "imposed" controlled conditions. These population studies then tell us that habitual circadian and sleep-timing differences are associated with some of the same broader cardiometabolic characteristics in everyday life.

Time-Zone Geography: A Natural Experiment

Giuntella, O., & Mazzonna, F. (2019). Sunset time and the economic effects of social jetlag: Evidence from US time zone borders. Journal of Health Economics, 65, 210–226. https://doi.org/10.1016/j.jhealeco.2019.03.007

Why it matters: Exceptionally relevant natural experiment. Researchers compared populations living on opposite sides of U.S. time-zone boundaries, where the social clock changes abruptly but geography and many other characteristics change much more gradually. People exposed to approximately one additional hour of natural evening light slept about 19 minutes less per night on average and were more likely to report insufficient sleep. The study also found differences in obesity, diabetes, cardiovascular disease and other health outcomes.
Important limitation: The disease outcomes are observational. The study does not prove that later sunset caused those diseases.

Relevance to DST in Alberta: Permanent DST effectively shifts government imposed one social-clock hour toward later solar time without moving their homes geographically west. We should not predict that Albertans will lose exactly 19 minutes of sleep, but the study provides strong reason to investigate whether sleep changes after the clock shift.

Seasonal Light, Circadian Biology and Depression

Tonini, E., Crouse, J. J., Shin, M., et al. (2026). Clinical and genetic correlates of a circadian subtype of depression in the Australian Genetics of Depression Study. The British Journal of Psychiatry. https://doi.org/10.1192/bjp.2026.10798

Why it matters: Important new research examining a proposed circadian subtype of depression. Approximately 23% of the depression sample met the proposed circadian-subtype criteria, which included features such as social jet lag, delayed sleep timing, evening chronotype, morning tiredness, hypersomnia and seasonal patterns. The circadian group also showed genetic relationships with later sleep timing and several metabolic and inflammatory characteristics, including BMI, triglycerides, inflammation and insulin resistance.
Important limitation: This is emerging science, epigenetics, etc. The authors call for independent replication. It does not demonstrate that circadian disruption causes approximately one quarter of depression, nor does it establish “circadian depression” as a settled clinical diagnosis.

Lam, R. W., Mistlberger, R. E., Baylis, P., & Choi, A. (2026). Analysis of health impacts associated with adopting permanent standard time or permanent daylight saving time to inform policy in Canada. CMAJ, 198, E1335–E1340. https://doi.org/10.1503/cmaj.261089

Why it matters here as well: The Canadian analysis discusses seasonal mood, sleep, energy and concentration in relation to winter light and specifically considers the importance of Canada's northern latitude.

Historical Context

United States, 1974. The United States introduced year-round daylight saving time during the energy crisis in January 1974. The experiment had been intended to continue longer but was reversed during the same year, restoring standard time during winter.

United Kingdom, 1968–1971. Britain maintained clocks one hour ahead throughout the year during the British Standard Time experiment before returning to seasonal clock changes.

Russia, 2011–2014. Russia adopted permanent DST in 2011 and abandoned it in 2014, moving to permanent standard or winter time following widespread dissatisfaction, including concerns about very dark winter mornings.

Thoughts: These social experiments do show that permanent DST has been tried at scale before and that dark winter mornings repeatedly became an important enough of a practical and political concern that the politicians reverted back.

Evidence Summary

There is strong experimental and systematic-review evidence that:

Light is a major environmental regulator of human circadian timing.
Light has acute alerting effects independent of its longer-term circadian effects.
Bright light after awakening can modify the cortisol awakening response.
Adolescents are biologically shifted toward later circadian timing.
Experimental sleep restriction increases adolescent sleepiness and inattention and impairs classroom learning.
Later school starts increase sleep duration and are associated with better youth outcomes.
Controlled circadian misalignment impairs glucose tolerance and insulin sensitivity.
Severe experimental circadian misalignment can rapidly produce adverse metabolic and cardiovascular changes.

There is substantial observational and quasi-experimental evidence that:

Later solar timing relative to social schedules is associated with shorter sleep.
Social jet lag is associated with adiposity and several cardiometabolic risk markers.
Morning solar timing is associated with differences in student academic performance.
Teacher sleep and daytime functioning respond to school timing.
Circadian disruption is associated with important aspects of mood and mental health.

The available evidence does not establish that permanent DST will cause obesity, diabetes, cardiovascular disease, depression or poorer academic achievement but clearly it will contribute to those outcomes. The evidence establishes that morning light, sleep timing and circadian alignment influence alertness, learning readiness, metabolic regulation and health, and that later solar timing relative to fixed social schedules has measurable consequences. Alberta has now shifted that relationship by one hour across an entire population. That is a strong scientific reason to not take this course.