The distinction between the two options is not merely a matter of preference on the clock face. Permanent daylight saving time keeps evenings lighter, which may support recreation, social activity, commuting, and certain forms of economic activity. But it also pushes sunrise an hour later, leaving more people waking up, travelling to school, and commuting to work in darkness during the winter months. Permanent standard time, by contrast, preserves more morning light and better aligns clock time with the internal biological rhythms that govern sleep, mood, and alertness. The trade-off is that evenings become darker earlier, a shift that many people find unappealing but that the authors argue carries fewer health costs than the alternative.

At the heart of the argument lies circadian science. The human body maintains an internal clock of roughly 24 hours, and this clock depends on environmental cues, particularly light, to remain synchronized with the external day. Morning light advances and stabilizes the circadian system, while evening light delays it. Under permanent daylight saving time, the clock is shifted an hour relative to solar time, which means that during winter, people receive less light in the morning and more in the evening. This combination works directly against circadian alignment. Dr. Ralph Mistlberger, professor of psychology at Simon Fraser University in Vancouver, explains the mechanism plainly: our biological clocks need morning light to stay synchronized with the 24-hour day, and permanent daylight saving time moves that light an hour later just when winter mornings are already darkest.

The consequences of circadian misalignment are not abstract. The analysis highlights effects on mood and sleep as potentially the most significant. An estimated 1 to 3 percent of people in Canada experience seasonal affective disorder, a form of depression linked to reduced light exposure in winter, while as many as 15 percent experience milder seasonal changes in mood, sleep, appetite, and energy. Because permanent daylight saving time delays sunrise, it shortens the natural morning light exposure that helps regulate these seasonal patterns. Geographic studies cited by the authors add a further layer of evidence: people living farther west within a time zone, where solar events occur later by the clock, experience several adverse health outcomes, a natural experiment that mirrors what permanent daylight saving time would impose on the entire population.

Certain groups may be especially vulnerable to the effects of later sunrise. Children and adolescents are of particular concern because puberty naturally shifts sleep timing later, while school start times remain early; delaying sunrise by an hour compounds an existing tension between biology and schedules. The authors also identify shift workers and early-start workers, public transit users, pedestrians and cyclists, and people living in rural or lower-income communities with poorer lighting and transportation infrastructure as potentially affected populations. For these groups, dark winter mornings are not simply an inconvenience but a matter of safety, sleep quality, and daily functioning.

Yet the analysis does not dismiss the appeal of permanent daylight saving time. Longer evening light genuinely makes it easier to exercise, socialize, or shop after work and school, and these benefits are real. Dr. Patrick Baylis, associate professor at the Vancouver School of Economics at the University of British Columbia, notes that the attraction is easy to understand because people like more light after work and school. But he cautions that those evening benefits must be weighed against evidence linking later solar time with less sleep, lower productivity, and worse educational outcomes. In economic terms, the question becomes whether the measurable gains in evening activity outweigh the documented costs to sleep, learning, and health.

International experience offers cautionary lessons for policymakers considering the change. The United States adopted permanent daylight saving time during the 1974 energy crisis but reversed the policy within a year amid public opposition to dark winter mornings and concerns about children travelling to school before sunrise. Russia adopted permanent daylight saving time in 2011 and reversed it in 2014 following public dissatisfaction. Chile similarly reversed a national move to permanent daylight saving time after its 2015 experiment. These reversals suggest that the political durability of permanent daylight saving time may be tested most severely in the first winter, when the consequences of late sunrises become impossible to ignore.

The authors emphasize that whichever policy governments ultimately choose, its effects should be actively monitored rather than assumed away. If permanent daylight saving time is adopted, possible mitigation measures include safer roads and pedestrian infrastructure, later or more flexible school and work start times, increased morning light exposure in schools and workplaces, and systematic monitoring of sleep, mood, injuries, and other health outcomes. Permanent standard time, by contrast, would require fewer compensatory measures, mainly addressing earlier evening darkness in winter and earlier dawn in summer. This asymmetry in required interventions is itself informative: the option that demands less remediation is also the option better aligned with human physiology.

Dr. Alexandra Choi, medical health officer with Vancouver Coastal Health, frames the issue in explicitly public health terms, arguing that time policy is public health policy. Her message to governments is that if they choose permanent daylight saving time, they should plan for the consequences before the first winter arrives, from safer morning travel and flexible start times to monitoring of sleep, mental health, and injuries. This preventive framing shifts the debate from a question of convenience to one of population health management, placing time policy alongside other structural determinants of health that governments routinely regulate.

The analysis closes with a reframing of the entire debate. Dr. Raymond Lam, professor of psychiatry at the University of British Columbia and lead author, observes that researchers and policymakers have focused for years on whether to stop changing the clocks, but that the more important question now is what happens the morning after they stop. As Canadian jurisdictions prepare to legislate the end of clock changes, the scientific consensus emerging from sleep and chronobiology research, echoed by major professional organizations that recommend permanent standard time, suggests that the morning after matters most. Aligning civil time with solar time in winter would preserve the morning light on which circadian health, sleep, and mood depend, even at the cost of darker evenings. The decision, the authors argue, should be made with eyes open to the evidence rather than to the calendar alone.

Subject of Research: Health impacts of adopting permanent standard time versus permanent daylight saving time

Article Title: When the clocks stop changing: What time is best for health?

Article References: When the clocks stop changing: What time is best for health?. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: standard time, daylight saving time, circadian rhythm, seasonal affective disorder, sleep, public health, clock changes, morning light, Canada, chronobiology, time policy, CMAJ

The epidemiological backbone of the review comes from large longitudinal cohorts. In a meta-analysis pooling more than 474,000 participants across eight countries with follow-up periods of 7 to 25 years, Cappuccio and colleagues found that habitual sleep of less than six hours per night was associated with a 48 percent higher risk of developing or dying from coronary heart disease and a 15 percent increase in the risk of fatal or nonfatal stroke. Other analyses reported that people sleeping under six hours were roughly twice as likely to experience myocardial infarction or stroke as those sleeping seven to eight hours, an effect most pronounced in middle-aged adults, precisely the stage of life when work and family demands most often erode sleep. The relationship follows a U-shaped curve: both short and unusually long sleep durations outside the six-to-nine-hour range carry elevated cardiovascular risk, complicating any simple prescription to simply sleep more.

Blood pressure provides one of the clearest mechanistic windows. In a cohort of 4,810 adults followed for a decade, those habitually sleeping five hours or less had an adjusted hazard ratio of 2.10 for developing hypertension, and the Sleep Heart Health Study, spanning nearly 6,000 men and women, found adjusted odds ratios of 1.66 for people sleeping under six hours compared with seven to eight. The physiological consequences of even acute restriction are measurable in young, healthy volunteers: a single night of sleep deprivation raised 24-hour systolic blood pressure by 5.2 mmHg and heart rate by 3.8 beats per minute, while total sleep deprivation produced persistent tachycardia in response to acute stress. Over twenty years, researchers tracking 495 healthy adults found that each hour of reduced sleep was associated with a 33 percent higher risk of coronary artery calcification, a direct structural footprint of chronic sleep debt inside the vessel wall.

The review details the neuroendocrine machinery behind these numbers. Sleep restriction activates the sympathetic nervous system, sustaining a pre-hypertensive, pro-atherogenic state of vasoconstriction, endothelial dysfunction, and impaired vascular repair. Simultaneously, the hypothalamic-pituitary-adrenal axis is perturbed: after just two nights of four-hour sleep, healthy young men showed ACTH and cortisol levels elevated by 19 and 21 percent respectively, and sleep-restricted women lost the normal daytime decline in cortisol, prolonging exposure to a hormone that drives vasoconstriction and hypertension. Sleep loss also suppresses growth hormone, which is secreted predominantly during deep N3 slow-wave sleep and is essential for maintaining the arterial endothelium and myocardial mass; growth hormone deficiency is linked to accelerated atherosclerosis and heightened heart failure risk. During intact N3 sleep, parasympathetic tone rises and blood pressure and heart rate fall, making deep sleep a nightly window of cardiovascular recovery that curtailed sleep systematically erodes.

Perhaps the most vivid natural experiment cited is the annual daylight saving time transition, which acutely deprives more than 1.5 billion people of roughly one hour of sleep. Analyzing hospital records, Sadhu and colleagues found a 24 percent increase in myocardial infarctions the day after the spring clock change, and a 21 percent decrease the day after the fall change when people gain an hour. Yet the authors urge caution: the effects are transient, derived from observational data, and recent large-scale studies in Ireland and the United States found no significant difference in heart attack incidence during transition weeks. The divergence illustrates a broader theme of the review, that circadian effects on cardiovascular outcomes are real in controlled settings but often modest, context-dependent, and easily obscured by comorbidities, activity patterns, and healthcare system factors in the messy real world.

On the metabolic side, the evidence is equally convergent. In a landmark experiment by Van Cauter’s group, eleven healthy young men restricted to four hours of sleep for six nights showed a 40 percent drop in glucose clearance and a 30 percent lower insulin response, a profile the authors described as comparable to a prediabetic state, which partially reversed after recovery sleep. A six-week study in 38 women found increased insulin resistance during short sleep independent of adiposity, and population studies across cultures consistently tie habitual short sleep to type 2 diabetes, with short sleepers showing higher HbA1c levels. The economic stakes are enormous: the American Diabetes Association estimated diabetes-related health costs at 300 billion dollars annually, with obesity-associated costs reaching two trillion.

Appetite regulation offers a second metabolic pathway. Sleep loss raises ghrelin, the stomach-derived hunger signal, and lowers leptin, the adipose-derived satiety signal; short sleepers showed ghrelin levels 14 percent higher than normal sleepers. Sleep restriction also elevates endocannabinoids such as 2-arachidonoylglycerol, which decline more slowly in the evening and sustain cravings for palatable food, a hormonal profile functionally reminiscent of cannabis-induced munchies. The behavioral consequences are quantifiable: a meta-analysis of 17 trials found partial sleep deprivation increased daily intake by roughly 253 calories, with cravings for salty, sugary, and starchy foods rising 30 to 40 percent while protein, fruit, and vegetable intake rose only modestly. Neuroimaging explains the shift: after total sleep deprivation, the amygdala over-responds to images of energy-dense food while prefrontal executive control weakens, and participants desired roughly 600 additional calories. Crucially, energy expenditure barely changes, rising by only about 134 kilocalories even under total sleep deprivation, so the extra intake lands as a net surplus, producing measurable weight gain and visceral fat accumulation in controlled trials.

The review extends the picture to the gut microbiome and circadian misalignment. Sleep disruption shifts the balance of intestinal bacteria, decreasing Bacteroidetes and increasing Firmicutes, a ratio associated with obesity and insulin resistance, while elevated cortisol promotes pathogenic bacterial growth. Shift workers show elevated tumor necrosis factor alpha and interleukin 6 alongside reduced adiponectin, an anti-inflammatory, insulin-sensitizing protein, providing an inflammatory route from circadian disruption to metabolic syndrome. Social jet lag, the mismatch between biological chronotype and socially imposed sleep timing, tracks with body mass index, waist circumference, C-reactive protein, and HbA1c in community cohorts, and even in adolescents, greater social jet lag and morning circadian misalignment correlate with reduced insulin sensitivity. In children, short sleep is associated with a 35 to 41 percent higher likelihood of obesity, and sleep restriction during dieting redirects weight loss away from fat and toward lean tissue, undermining the metabolic benefits of caloric restriction.

Encouragingly, the review highlights early interventional evidence that the damage is partly reversible. Extending sleep from 6.5 to 8.5 hours per night for two weeks reduced appetite by 14 percent and cravings for unhealthy snacks by 65 percent in overweight adults. A four-week sleep extension trial cut daily sugar intake by 9.6 grams, another study improved blood pressure with a 35-minute nightly sleep increase, and six weeks of one extra hour of sleep significantly improved insulin sensitivity in habitually short sleepers. The authors caution that much of the literature remains observational, that mechanistic studies have skewed toward male participants, and that causal inference is limited by possible reverse causality. They call for longitudinal designs combining sleep phenotyping with multi-omics profiling, and for trials testing whether sleep extension, cognitive behavioral therapy for insomnia, or treatment of sleep-disordered breathing can restore hormonal homeostasis. As modern life continues to compress sleep, the message is that a good night’s rest is not a luxury but a measurable pillar of cardiovascular and metabolic prevention.

Subject of Research: The effects of sleep deprivation and circadian misalignment on cardiovascular and metabolic disease risk

Article Title: Sleep loss as a cardiometabolic risk factor: a narrative review of clinical and public health implications

Article References: Ghanem, F. K., Attarian, H., Al-Khalil, Z., & Kabrita, C. S. (2026). Sleep loss as a cardiometabolic risk factor: a narrative review of clinical and public health implications. Journal of Clinical Sleep Medicine, 22(1), Article 129. https://doi.org/10.1007/s44470-026-00144-1

Image Credits: AI Generated

DOI: 10.1007/s44470-026-00144-1

Keywords: sleep deprivation, cardiometabolic disease, circadian misalignment, hypertension, insulin resistance, obesity, leptin, ghrelin, endocannabinoids, metabolic syndrome, slow-wave sleep, daylight saving time