On the last Sunday of March, at 2 a.m., it suddenly becomes 3 a.m. On paper, one hour less. On the wrists of 11,780 adults monitored in the United Kingdom and equipped with accelerometers, reality was somewhat heavier: that Sunday, they slept an average of 65 minutes less than the previous Sunday. And the internal clock doesn't reset with a gesture, while mornings become dark again.
This guide brings together studies identified via PubMed: the biological clock, the difference between spring and autumn, sleep, the road, the heart and mood, distinguished registries and trials, then what helps with adaptation, with a 7-day protocol.
What is observed : in spring, the clock must move forward one hour, a direction more difficult than the autumn setback. The night of Sunday shortens by approximately one hour on average, and adaptation generally takes a few days, more so in "night owls" and adolescents. Registries associate the following week with slightly more heart attacks (4 to 5% according to two meta-analyses) and fatal accidents in the morning: associations. Regarding mood and suicide, studies are conflicting.
What helps : moving bedtime, wake time, and meals forward in increments on the days before, seeking bright light immediately upon waking, dimming lights and screens in the evening, keeping caffeine for the morning, taking a short nap, and exercising extra caution while driving Monday morning. In trials, melatonin advances the clock when taken in the afternoon, at specific doses and times.
- What happens in the body on the last Sunday of March
- Why spring is more difficult than autumn
- Night owls and adolescents on the front lines
- Sleep: how long to adapt
- Vigilance, driving, work and errors
- Heart and stroke: what meta-analyses say
- Mood and mental health: conflicting results
- Morning light, the primary lever
- Melatonin: what phase advance trials show
- Exercise, caffeine, naps, meals and magnesium
- The 7-day protocol, children and seniors included
- Daylight saving time or standard time year-round: the debate among chronobiologists
- Frequently asked questions
What happens in the body on the last Sunday of March
A central clock in the brain regulates each day the time at which melatonin rises in the evening and alertness returns in the morning. It resets to a dominant signal: light, morning light that advances it, evening light that delays it.
On Monday, the alarm goes off at 7 o'clock; for a body still set to standard time, it is 6 o'clock. In a survey of 55,000 people, sleep time on free days followed the seasonal progression of dawn under standard time, but not under daylight saving time; in 50 people monitored for 8 weeks around each time change, sleep and activity adjusted easily in the fall, whereas in spring the activity time did not adjust, especially in "evening" people. The authors conclude that the human clock does not adjust to daylight saving time; their measurement focused on sleep and activity schedules, not on a biological marker of the clock.
Light also shifts: daylight saving time makes mornings darker and evenings brighter, as recalled by an analysis of American road traffic records. We wake up deprived of the signal that advances the clock, and we receive more light in the evening, which delays it.
In 11,780 adults aged 43 to 78, sleep duration on the daylight saving time Sunday was on average 65 minutes less than the previous Sunday, and 61 minutes less than the following Sunday. The authors note a slight recovery of sleep on the following weekdays. A comparison between individuals, not within the same individuals.
de Lange MA, Richmond RC, Birnie K, et al. J Sleep Res 2025;34(3):e14335. DOI: 10.1111/jsr.14335
We speak ofphase advance when the clock shifts earlier, of phase delay when it shifts later: spring requires a one-hour advance, fall a delay.
Why spring is more difficult than fall
Going to bed later, as in fall, is generally easier than going to bed earlier. A team of chronobiologists summarizes this in a trial on eastbound flights: humans generally take longer to readjust after a phase advance than after a delay.
The transition to daylight saving time imposes this one-day advance, with a shortened night. That said: fall is not without effect.
| What is measured | In spring | In fall |
|---|---|---|
| Sunday sleep, 11,780 adults | 65 minutes less than the previous Sunday | 33 minutes more than the previous Sunday |
| Sleep symptoms the following week, 30,097 people aged 45 to 85 | 9 minutes less sleep, no other difference | More sleep onset insomnia (7.1% versus 3.3%) and dissatisfaction |
In this Canadian cohort, autumn was associated with a transient increase in several disorders: spring is harsher for the clock and the first night, not on all indicators.
Night owls and adolescents on the front line
Chronotype refers to the time at which each person is naturally inclined to sleep. A systematic review of 27 studies (participants aged 6 to 85 years) associates the shift to daylight saving time with shorter, lower quality sleep and increased drowsiness, especially among evening chronotypes, while highlighting the heterogeneity of the studies.
Adolescents combine a naturally late-shifted clock and fixed class schedules. In German students, drowsiness remained higher until the third week after the change, more so in older students and evening types.
In 35 American high school students monitored by actigraphy on school days before and after the shift to daylight saving time, sleep decreased by an average of 32 minutes per night during the week, or 2 hours 42 minutes of lost sleep over the week compared to the reference week. Reaction time, attention errors, and drowsiness increased.
Medina D, Ebben M, Milrad S, et al. J Clin Sleep Med 2015;11(8):879-884. DOI: 10.5664/jcsm.4938
At work, among 155 employees surveyed three Mondays around the change, engagement was lower the next day and one week later, partly due to lower quality sleep, and more so in "evening type" people on the first day. A signal, on a small sample.
Sleep: how long to adapt
A consistent pattern from one study to another: a shortened first night, a few slightly shorter nights, then a gradual return, slower in evening types.
Recent work adds a clue: in 37 students aged 18 to 22, 85% of those who ate low-fat had shifted their sleep by one hour by Monday, versus 57% of those whose more than 40% of calories came from fats; 29% of the latter (a group of 7 people) had not done so by Friday. An observational study on a small sample, which does not prove that diet is the cause.
| Study | Population | What is observed after the spring shift |
|---|---|---|
| Accelerometer, de Lange, 2025 | 11,780 adults aged 43 to 78, United Kingdom | 65 minutes less sleep on Sunday, slight recovery afterwards |
| Actigraphy, Medina, 2015 | 35 high school students, United States | 32 minutes less per weeknight, degraded vigilance |
| Actigraphy and melatonin, McHill, 2024 | 37 students, United States | Readjustment within 4 days maximum with a low-fat diet, slower with a high-fat diet |
For most adults, discomfort is concentrated in the first few days. The idea of never complete adaptation is based mainly on the 8-week follow-up mentioned above: plausible, but still debated.
Alertness, driving, work and errors
In an American registry of 732,835 fatal accidents from 1996 to 2017, the shift to daylight saving time was associated with a 6% increase in risk, more pronounced in the morning and in the western time zones. The increase diminished over the week, and nothing appeared after the shift back to standard time.
Among 375,658 fatal accidents in the United States from 2012 to 2022, comparing states that change the clocks to two states that do not, the total number of fatal accidents did not vary after the spring time change (+0.2%, not significant). Conversely, fatal accidents between 6 and 10 a.m. increased by 25.9% in the two weeks following the change, compared to the two weeks before and to control states.
Lei D, Du Y, Peng S, et al. Accid Anal Prev 2026;237:108719. DOI: 10.1016/j.aap.2026.108719
The only study cited here comparing states that do not change the clocks, it suggests that part of the increase is due to the season, but that an excess of morning accidents persists, without separating sleep deprivation, shifted circadian rhythm, darkness and traffic. In practice: exercise caution while driving on weekday mornings of the following week, especially on Monday.
For workplace accidents, results diverge. In American mines, from 1983 to 2006, the Monday following the spring time change saw more workplace accidents, and more serious ones, than other days; time-use data indicated 40 minutes less sleep that Monday, and nothing similar appeared after the return to standard time. A more recent analysis of 738,828 workplace accidents reported in 2023 by large American companies (100 or more employees) found no significant increase after the spring time change, but an increase after the fall change, while a review of 157 studies published in 2026 associates the fall change with fewer workplace accidents. Sectors, periods and methods differ: for work, the effect of the spring change remains uncertain. On the healthcare side, among 288,432 medical malpractice complaints in the United States, the spring time change was associated with higher indemnities, but not with more serious incidents: a modest and indirect signal.
Heart and stroke: what meta-analyses say
The most recent meta-analysis brings together 12 studies conducted in 10 countries : the relative risk of heart attack in the weeks following the spring time change was 1.04, or 4% higher, versus 1.02, not significant, after the fall time change; after exclusion of one inconsistent study, 1.04 in spring and 1.00 in fall. The authors speak of a possibly increased risk, with moderate to marked heterogeneity.
Among more than 115,000 people, the risk of heart attack increased slightly after the spring time change (odds ratio of 1.05, or approximately 5%), but not the week following the fall time change (1.01). The two changes analyzed together yielded 1.03 over the following two weeks. Results did not differ by age or sex.
Manfredini R, Fabbian F, Cappadona R, et al. J Clin Med 2019;8(3):404. DOI: 10.3390/jcm8030404
Forischemic stroke, a Finnish registry from 2004 to 2013 found 8% more hospitalizations in the first two days following a time change, but not over the entire week; age over 65 was associated with increased risk on those first two days (relative risk of 1.20). These figures cover both time changes combined : they do not allow isolation of spring.
An English study found almost nothing: among 683,809 people who consulted for one of the studied conditions from 2008 to 2019, the spring time change was barely associated with variation in acute cardiovascular disease, anxiety disorders, depression or sleep disorders, or road accidents. Individual risk remains low.
These data compare the week of the change to control weeks without being able to rule out all other factors (weather, season, holidays). These are associations : the proposed mechanism, shortened night and shifted circadian rhythm, is plausible but not proven.
Mood and mental health: discordant results
In a Danish registry from 1995 to 2012 (185,419 hospital contacts for depression), the shift to daylight saving time was not associated with any variation; it was the shift back to standard time that was associated with an 11% increase.
For suicide, data are discordant. A pre-registered study on Austria, Switzerland and Sweden from 1980 to 2022 (13,362 suicides around the spring time change) found no increase (rate ratio of 0.98). An econometric analysis of American data from 1979 to 1988 estimated instead an increase of 6.25% shortly after the spring change. A systematic review of 157 studies in 36 countries, published in 2026, found no clear and consistent effect on psychiatric disorders.
| Effect | After the spring time change | Evidence level |
|---|---|---|
| Sleep | Shortened Sunday night, shorter week for some people | Objective measures, consistent across studies |
| Fatal road accidents | Increases in the morning; overall effect uncertain once the season is taken into account | Registries, associations |
| Workplace accidents | Increase in mines (1983 to 2006), no significant increase in 2023 | Discordant registries |
| Heart attack | 4 to 5% higher risk (1.04 to 1.05) | Two meta-analyses of registries, heterogeneity |
| Ischemic stroke | Not isolated: +8% the first two days, two confounded changes | One national registry |
| Depression | No variation (Danish registry) | Registry, associations |
| Suicide | No increase in three European countries, estimated increase in the United States in the 1980s | Discordant registries |
If you know you are sensitive to short nights, protect your sleep during the week of the time change (practical advice). Saffron is studied for sleep: in 165 adults suffering from moderate insomnia, 20 or 30 mg per day of a standardized extract, taken in the evening approximately one hour before bedtime for 4 weeks, reduced insomnia symptoms slightly more than placebo (approximately one point on a 24-point scale). It is the same extract as that in our Saffron, 30 mg per capsule to be taken in the morning with a meal; two co-authors are affiliated with the company that manufactures the extract, the timing of administration in the trial (evening) differs from that of our capsule (morning), and the trial was not conducted on time change or seasonal depression (see our article saffron and sleep). Saffron is not recommended during pregnancy, breastfeeding, or before age 12, and requires medical advice when taking antidepressants, anxiolytics, or anticoagulants.
Morning light, the primary lever
The best-studied clock advancement protocols, designed to prepare for eastward travel, are based on light.
In 28 healthy young adults, sleep time was advanced by one hour per day for 3 days. Based on the light received during the 3.5 hours following waking, the melatonin rise time advanced by 0.6 hours in weak interior light (less than 60 lux), by 1.5 hours in intermittent bright light, and by 2.1 hours in continuous bright light (more than 3,000 lux).
Burgess HJ, Crowley SJ, Gazda CJ, et al. J Biol Rhythms 2003;18(4):318-328. DOI: 10.1177/0748730403253585
Advancing faster is not better: in 26 adults receiving bright light of approximately 5,000 lux in the morning, advancing sleep by 2 hours per day did not perform significantly better than one hour per day (median advances of 1.9 and 1.4 hours), and the rapid group had difficulty falling asleep by the third day.
In the evening, the challenge is reversed: in 116 young adults, ordinary room light (less than 200 lux) received within 8 hours before bedtime delayed melatonin rise in 99% of them and shortened its secretion by approximately 90 minutes, compared to dimmed light.
Shutters open upon waking, breakfast near a window, 20 to 30 minutes outdoors in the morning; in the evening, low and warm lamps (practical guidelines drawn from the trials).
At the end of March, winter has left its traces. Vitamin D is primarily produced in skin exposed to sunlight: in a standardized analysis of 55,844 Europeans, 17.7% of those sampled from October to March had a level below 30 nmol/L, compared to 8.3% in summer, and 40.4% overall were below 50 nmol/L. This is a logical time to review your intake, regardless of the time change; see our guide when and how to take vitamin D.
Regarding mood, let's be measured: a meta-analysis of 31 trials (24,189 participants) associates each 1,000 IU per day increment with a small reduction in depressive symptoms (effect size of −0.32, moderate certainty), but the effect is no longer significant in trials lasting more than 24 weeks, and a review of 11 studies on seasonal depression, including 5 on nutritional interventions, finds no benefit from vitamin D or B12 supplementation. Results are discordant; we identified no trials on daylight saving time adaptation, and we attribute no effect to it on sleep. Pregnancy or breastfeeding: consult a practitioner.
Melatonin: what phase advance trials show
Melatonin shifts the clock in one direction or the other depending on the time of intake. To advance it, as in spring, trials administer it in the afternoon or early evening, several hours before the rise of natural melatonin.
In 34 adults aged 18 to 42, 0.5 mg of melatonin taken daily for 3 days produced the greatest phase advances when taken in the afternoon, 2 to 4 hours before the rise of natural melatonin, or 9 to 11 hours before midnight. Taken shortly after waking, it instead delayed the clock. Each at its optimal time, later for 0.5 mg, doses of 0.5 and 3 mg produced comparable shifts.
Burgess HJ, Revell VL, Molina TA, et al. J Clin Endocrinol Metab 2010;95(7):3325-3331. DOI: 10.1210/jc.2009-2590
Combined with light, it adds a little: in 44 adults aged 19 to 45, three days of waking advanced by one hour daily with bright morning light advanced the clock by 1.7 hours under placebo, 2.5 hours with 0.5 mg, and 2.6 hours with 3 mg of melatonin taken in the afternoon. In sleep phase delay, a meta-analysis of 9 trials (91 adults, 226 children; doses and timings varying across trials) shows an advance of approximately 1.2 hours in natural melatonin and faster sleep onset of approximately 23 minutes.
In jet lag, a review of 10 trials identified another approach: 0.5 to 5 mg taken at the intended bedtime, between 10 p.m. and midnight, at the destination, after flights crossing at least five time zones. One hour of adjustment and five time zones are two very different situations.
Our Optimal Sleep provides 1.9 mg of melatonin with lemon balm 100 mg, hops 100 mg, passionflower 50 mg, and valerian extract 50 mg, to be taken 45 minutes before bedtime with a large glass of water. No trial has tested this formula, and its dose and timing of intake differ from those in phase advance trials, which used 0.5 or 3 mg in the afternoon. It fits rather into an evening ritual, to discover what may help better prepare you for sleep. Not recommended for children under 12 years old.
Taking it at the wrong time, early in the day, can cause drowsiness and delay adaptation, according to the jet lag review, which also reports cases in people with epilepsy and patients on warfarin, an anticoagulant: in these situations, consult your doctor. A review of 37 trials (0.15 to 12 mg, most often 4 weeks or less) notes mainly daytime drowsiness (1.66%), headaches and dizziness (0.74% each), most often transient, and deems data insufficient on prolonged use and in potentially vulnerable people, such as children before adolescence and people with epilepsy or asthma.
Exercise, caffeine, naps, meals, and magnesium
Exercise. In 51 adults aged 59 to 75 and 48 aged 18 to 30, one hour of moderate treadmill exercise, three days in a row, advanced the clock when performed at 7 a.m. or between 1 and 4 p.m., and delayed it between 7 and 10 p.m., with no difference by age. In spring, move rather in the morning or early afternoon, outdoors if possible.
Caffeine. In a controlled trial in 5 adults, the equivalent of a double espresso 3 hours before bed delayed the clock by approximately 40 minutes, nearly half the effect of 3 hours of bright light at bedtime: the opposite of what we want in March. Keep coffee for the morning (see our article caffeine, dosage, timing and sleep).
Naps. After a shortened night of 5 hours, in 24 young adults, a 10-minute nap at 3 p.m. immediately improved alertness and performance; a 30-minute nap first caused a period of grogginess.
Meals. In 10 young men, delaying meals by 5 hours over 6 days did not change melatonin or cortisol, markers of the central clock, but shifted blood glucose rhythm by 5.69 hours. Advancing meals before the time change transposes this principle, tested in the opposite direction. Evening alcohol should also be limited that week (practical advice).
Magnesium. A meta-analysis of 3 trials in 151 older adults with insomnia found faster sleep onset of approximately 17 minutes, with no significant gain in sleep duration, with low to very low quality evidence; forms and doses varied, and no trial addressed the time change. Our Magnesium+ combines microencapsulated magnesium oxide, magnesium malate, taurine and vitamin B6, at a rate of 4 capsules per day; it was not tested in these trials.
The 7-day protocol, including children and seniors
Practical advice, not a protocol tested as such: the trials advanced sleep by one hour per day in the laboratory, with bright light; at home, smaller increments are easier to maintain.
Children and babies. We identified no study dedicated to babies and young children; for practical purposes, shift bedtime, naps and meals by 10 to 15 minutes per day on the preceding days, provide light in the morning and keep the bedroom dark in the evening. No melatonin for a child without medical advice; our Optimal Sleep is not recommended for children under 12.
Seniors. Among 45 to 85 year-olds in the Canadian cohort, spring was associated with only 9 minutes less sleep; exercise shifted their clock as it did for young adults. In the Finnish registry, two changes combined, an age over 65 was associated with increased stroke risk in the first two days: know the warning signs and call 15 or 112 if they occur.
Consult if insomnia persists beyond a few weeks, if drowsiness persists or bothers you while driving, if sadness or loss of interest lasts more than two weeks, or if you live with a mood disorder whose balance depends on sleep. Dark thoughts: 3114, day and night. Signs of heart attack or stroke: 15 or 112.
Daylight saving time or standard time year-round: the debate among chronobiologists
If time changes stopped, which time to keep? With permanent daylight saving time, clearer evenings and very dark winter mornings; with standard time, brighter mornings.
An international society of circadian rhythm researchers concludes, based on comparisons of large populations, that the benefits of a Permanent standard time outweigh the annual change and permanent daylight saving time. An American sleep medicine society supports the same option. A British sleep society, in 2025, judges sleep to be negatively affected by imposed time changes, especially the spring shift, and positively affected by morning light, and recommends standard time year-round.
The review of 157 studies published in 2026 provides nuance: the spring transition appears associated with more heart attacks and fatal accidents, but living on daylight saving time in summer appears associated with fewer deaths and accidents during that season, and standard time could be associated with slightly shorter nights in winter. Its authors judge the evidence limited and heterogeneous, and advocate for a balanced approach.
1.9 mg of melatonin, lemon balm, hops, passionflower and valerian, in a vegetable capsule to take with a large glass of water, 45 minutes before bedtime: an evening ritual for the week when the clocks spring forward.
See Optimal SleepAt the end of winter, our Vegetable Vitamin D3 in drops provides 1,000 IU per drop, derived from lichen.
Frequently asked questions
Why does daylight saving time cause so much fatigue?
Because it combines a shortened night and an advance of the internal clock, which is more difficult than a setback. In 11,780 adults, sleep on the Sunday of the change was 65 minutes shorter than the previous Sunday; in high school students, it decreased by 32 minutes per school night.
How long does it take to adapt to the March time change?
Usually a few days. In a study of students, those who ate low-fat diets had all shifted their sleep within 4 days, 85% by Monday. In adolescents, sleepiness remained elevated until the third week, and evening-type people adapt more slowly.
Is the spring time change worse than the fall one?
For the clock and the first night, yes, and registries link spring to a slight increase in heart attacks and fatal morning accidents. But fall also has its effects, on reported insomnia and depressive episodes in certain registries.
Does the transition to daylight saving time increase the risk of heart attack?
Two meta-analyses of registries find a relative risk or odds ratio of 1.04 to 1.05 in the days and weeks that follow, or 4 to 5% more, with no increase after the fall transition. These are associations, with heterogeneity between studies, and individual risk remains low.
Are there more road accidents after the time change?
An American registry associates the spring transition with 6% more fatal accidents, especially in the morning. An analysis with control states does not find an overall increase, but 25.9% more fatal accidents between 6 and 10 a.m. Drive carefully in the mornings that follow.
How do you prepare your body for the transition to daylight saving time?
By advancing bedtime, wake time and meals in 15 to 20 minute increments over the three days before, by getting daylight as soon as you wake up, by dimming lights and screens in the evening, by keeping coffee for the morning and by exercising in the morning or early afternoon (practical advice; advancing meals has not been tested for time changes).
Should you take melatonin for the time change?
It's not essential. In a trial of 44 adults, taken in the afternoon at 0.5 or 3 mg, it added nearly an hour of advancement over morning light within 3 days. Taking it too early in the day can cause drowsiness. Medical advice recommended in case of epilepsy or treatment with warfarin.
How do you help a baby or child transition to daylight saving time?
No studies dedicated to babies were identified; as a practical matter, shift bedtime, naps and meals by 10 to 15 minutes per day over a few days, give light in the morning and keep the bedroom dark in the evening. No melatonin without medical advice.
Does the March time change cause low mood?
The data do not show this clearly: no variation in depressive episodes in spring in a Danish registry, no increase in suicides in three European countries, an estimated increase in American data from the 1980s, and no clear psychiatric effect in a review of 157 studies.
Do scientists prefer daylight saving time or standard time year-round?
The three scientific societies cited here prefer permanent standard time, closer to the sun in the morning. However, a review of 157 studies calls for a balanced approach, daylight saving time in summer being also associated with certain benefits.
Sources
The studies cited below were identified via PubMed.
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- Revell VL, Burgess HJ, Gazda CJ, et al. Advancing human circadian rhythms with afternoon melatonin and morning bright intermittent light. Journal of Clinical Endocrinology and Metabolism, 2006;91(1):54-59. DOI
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- Roenneberg T, Wirz-Justice A, Skene DJ, et al. Why should we abolish daylight saving time? Journal of Biological Rhythms, 2019;34(3):227-230. DOI
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