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Increased heart attack risk among disruptive side effects of daylight-saving time

KITE-UHN sleep scientist Azadeh Yadollahi weighs in on the impacts of the time change

When we set clocks forward on March 14 and lose an hour of sleep in the switch to daylight saving time (DST), our routines are disrupted literally overnight. While most grudgingly accept this trade-off of sleep for more sun, others will find it damaging to their health. Research shows the reduced rest associated with the transition to DST can cause serious, lasting impacts on those with certain pre-existing medical conditions.

Working to uncover the many ties between sleep patterns and overall health is Dr. Azadeh Yadollahi. As lead scientist at SleepdB, Canada’s first soundproof sleep lab located within the KITE Research Institute, Yadollahi studies the physiological changes that occur during sleep. The innovations and technologies SleepdB develop enhance treatment for those with chronic disorders like sleep apnea and nocturnal asthma, and aim to reduce their risk of hospitalization.

A sudden change in body rhythm

Many biological processes are regulated by the body’s sleep-wake cycle, called the circadian rhythm. This cycle, in turn, is driven by natural cues in the environment like the length of sunlight in the day. According to Yadollahi, when clocks are changed for DST and a shortened sleep time is imposed on the body, it causes a sudden disruption to the flow of its internal rhythm.

“Vital biological systems and processes are finely tuned to work in a certain order, and daylight saving immediately interrupts this,” she says. “When we lose one hour of sleep, we push the body to do all the things that it’s used to doing over the night in a shorter span of time.”

Many people experience fatigue as a side effect from the time change as their bodies work to compensate for the lost hour of sleep and adjust to a new cycle. This is sometimes manifested through increased accident rates or a reduced ability to concentrate. Others may experience more acute side effects.

DST affects heart health

Although the connection between sleep and heart health may not seem obvious, it is known that when clocks move forward in the spring, heart attack rates go up. This risk is particularly high for those with underlying conditions, like a previous history of heart disease.

“The onset of daylight saving time results in an asynchrony between the heart’s normal routine and a new routine that’s being imposed on it,” explains Yadollahi. “This puts extra pressure on the heart, and if it’s compromised it might be harder for it to cope with this adjustment.”

The impact of DST on mood stability

Individuals who suffer from depression may also experience negative side effects when we spring forward to DST. Sleep is a time for the brain to learn from its daily experiences and to rest; these processes are interfered with when sleep patterns are disrupted.

“Switching over to daylight saving time interrupts the circadian rhythm and usually induces fatigue,” says Yadollahi. “If a person is already prone to depressive episodes, this could potentially increase the severity of their symptoms in the days that follow.”

The ripple effect of DST

Resetting the clock has a more profound effect than the simple loss of an hour’s sleep: When shifting to DST, the synchronization of social and biological routines is broken. 

“The body takes days to adapt to its new routine, creating a ripple effect after the time change occurs,” says Yadollahi. “The number of days needed for the internal clock to resynchronize varies from person to person, similar to the way we all differ in our ability to recover from jet lag.”

How to prevent the side effects of DST

Fortunately, there are things people can do that will lessen the impact of the sudden switch to DST. As with most health advice, it involves maintaining good habits and some advance planning.

“One week before the time change, it helps to go to bed and wake up slightly earlier than usual each day; when the time change eventually happens, the body will have had a chance to gradually acclimate to it,” says Yadollahi. “After the time change, getting out into the sunlight and exercising helps the body clock readjust, and so does eating a healthy breakfast first thing in the morning.”

Quick facts: COVID-19 and sleep

Although people report they are sleeping more during the pandemic, increased stress is thought to be responsible for these changes to sleep patterns:

  • More frequent dreaming
  • More frequent waking in the middle of the night