How Daylight Saving Time Worsens Insomnia and Circadian Rhythm Disorders

Why Does Daylight Saving Time Disrupt Sleep and Circadian Rhythms?

The human circadian system is anchored primarily by morning light exposure, which entrains the suprachiasmatic nucleus to the 24-hour solar day. When daylight saving time begins in spring, clocks move forward by one hour while the body's internal pacemaker remains tied to environmental light. The result is delayed melatonin onset, later sleep timing, and reduced morning light exposure—conditions that lab studies and field research have linked to fragmented sleep and impaired daytime alertness.

Patients with pre-existing insomnia or circadian rhythm sleep-wake disorders such as delayed sleep-wake phase disorder are particularly vulnerable. For these individuals, even small phase shifts can amplify difficulty initiating sleep, increase nocturnal awakenings, and worsen morning grogginess. Sleep medicine experts note that the misalignment persists for weeks—some research suggests months—because most people do not get sufficient morning sunlight to fully re-entrain.

What Are the Health Risks of the Spring Forward Time Change?

The Monday following the spring time change has been associated with measurable increases in acute myocardial infarction admissions in several observational analyses, alongside upticks in ischemic stroke and motor vehicle crashes. While the absolute risk increase is modest at the individual level, the population-wide impact is meaningful given that hundreds of millions of people are affected simultaneously. The fall transition appears less hazardous on average but still produces sleep disruption and mood effects in vulnerable populations.

For patients with mood disorders, the abrupt shift can precipitate depressive episodes, particularly in those with seasonal affective disorder or bipolar illness, where circadian stability is therapeutically important. Clinicians often advise gradual sleep schedule adjustments in the days before the transition, prioritizing morning bright light exposure and avoiding evening screens to support faster realignment.

Should Daylight Saving Time Be Abolished?

The American Academy of Sleep Medicine, the Sleep Research Society, and the European Biological Rhythms Society have published position statements calling for the elimination of seasonal clock changes. Their consensus favors permanent standard time rather than permanent daylight saving time, because standard time more closely matches local solar noon, supporting healthier morning light exposure and earlier sleep onset—both of which are protective for cardiometabolic and mental health.

Legislative debates in the United States and Europe have at times leaned toward making DST permanent, a move that sleep scientists warn would worsen chronic circadian misalignment, especially during winter months when sunrise would occur very late. Public health advocates argue that any policy change should be guided by circadian biology rather than commercial or recreational preferences.