The hazards of Daylight Saving Time: risks and tips

The switch to Daylight Saving Time (DST) has come and gone. If you’re like most Americans, you didn’t plan for it, and now you’re feeling sluggish and wonky.

Why time changes make us tired

What’s one lost hour? It doesn’t seem like much. In fact, for average Americans, the amount of sleep loss that correlates with the springtime change is about 40 minutes, according to the National Sleep Foundation (NSF).

You can expect to feel a little slow and sleepy until midweek following the time change, although the NSF points to a subset of Americans who may require an entire week to make the adjustment. There are two reasons why:

  1. Less light in the morning leads to body clock confusion. Morning sunlight cues your body to shut down melatonin release to encourage wakefulness. Waking up in the dark confuses the body clock, which wants you to keep sleeping.
  2. At night, later light can delay melatonin release, confusing the body clock into thinking that it’s not bedtime yet.

Gradually, of course, we adjust through a forced reset of our circadian rhythms, and the days naturally lengthen. Still, a confused body clock means we will need a few days to prompt our circadian rhythms to play along with the schedules we live our lives by. 

There are health and safety consequences caused by time changes that are not to be taken lightly. Research shows that the sleep deprivation that results means you run a temporarily higher risk for four major health and safety problems.

Four increased health risks related to DST



Finnish researchers have recently found a specific correlation between lost sleep due to DST and an increased risk for stroke. 

Sleep researcher Jori Ruuskanen MD, PhD analyzed stroke data from Finnish hospital registries between 2004 to 2013.

He confirmed an eight percent increase in stroke in those hospitalized during the week after [DST] compared with those who were hospitalized two weeks before or after the time change.

“Stroke risk is highest in the morning hours and we know from previous studies that DST change slightly shifts the timing pattern of stroke onset,” said Ruuskanen in a recent interview. “Previous studies have also shown that the disruption of the circadian clock due to other reasons—such as rotating shift work—and sleep fragmentation are associated with an increased risk of stroke.”


Heart Attack

Studies coming out of the University of Alabama at Birmingham (UAB) Division of Cardiovascular Disease suggest that for people with a history of heart problems, March’s “spring forward” can lead to an increased risk for heart attack.

Martin Young, PhD, researcher for the UAB study, said “Moving the clocks ahead one hour in March is associated with a 10 to 24 percent increase in the risk of having a heart attack the following Monday and to some degree Tuesday.”

He points out four factors that contribute to increased heart attack:

Other studies confirm these findings, including a Swedish one published in Sleep Medicine in 2012 which showed a distinct link between DST shifts and acute myocardial infarction (AMI).

Automobile Accidents

A 2001 study in Sleep Medicine showed that Monday mornings following DST resulted in increases in fatal automobile accidents.

The health consequences of DST shifts were shown to be both the result of physiological adjustments and changes in behavior caused by forced body clock adjustments.

A letter published in 1996 in the New England Journal of Medicine, from Stanley Coren, PhD at the University of British Columbia, spelled out public health and safety risks caused by lost sleep due to DST.

He wrote that it “might lead to an increased number of ‘microsleeps,’ or lapses of attention, during daily activities and thus might cause an increase in the probability of accidents, especially in traffic.”

Coren cited Canadian data on sleep deprivation and automobile collisions in his letter, writing that “the loss of merely one hour of sleep can increase the risk of traffic accidents” and that these accidents were “due to sleep loss rather than a nonspecific disruption in circadian rhythm.”

More recently, a Colorado University study showed ten years of research linked DST to fatal motor vehicle accidents (MVAs). The study, authored by Austin Smith, PhD illustrated that MVAs following the time change correlated with:

  • Disrupted sleep schedules that led to an increased risk for drowsy driving, and

  • Higher fatalities due to morning MVAs over the first six days following DST


Workplace Injuries

The Journal of Applied Psychology in 2009 reported research showing that sleep problems that come from recognizing the DST time shift, “intended to better align waking activity with daylight periods, have negative side effects on organizations.”

Their data showed that a loss of just 40 minutes of sleep led to a nearly six percent increase in workplace injuries following DST.

Employees who encountered workplace injuries lost nearly 70 percent more days from work because of it. The study's conclusion? “Schedule changes, such as those involved in switches to and from [DST], place employees in clear and present danger.”

Feeling sleepy?

Here are some tips for surviving the time shift.

What you can do now

If you were already sleep deprived going into DST, you will feel the effects more acutely.

What you can do later

Prepare for time shifts in advance by a few days. Time your bedtime and rise time for just 15 minutes earlier or later, depending upon whether it’s DST in the spring or Standard Time in the fall. In addition, avoid bright light one hour before bedtime and increase your exposure to bright light first thing in the morning.

Simple planning can help ease potential sleep loss so that the Monday morning following these time changes doesn’t result in a high-risk health day for you.

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