Where it is observed, Daylight Saving Time begins this year on Sunday, March 13, 2022. This transition from Standard Time was first enacted to conserve energy and shift the timing of our activities to match more daylight during evening hours.

The days grow longer and the nights get shorter as we head towards the summer solstice, which has been described as the longest day of the year. The extra sunshine and boost of Vitamin D may be a relief from the dark winter days and a sign of warmer weather ahead.

The extra daylight hours may allow for more fun in the sun, but we may want to consider how these changes in light and time can influence our circadian system and disrupt our sleep.

How does the circadian system detect the light/dark cycles?

The circadian system is a complex coordination of biological rhythms which help our body function. Derived from the Latin terms “circa” meaning “around” and “diem” meaning “day,” the human circadian system cycles a little longer than 24-hours and is influenced by external environmental cues. The strongest cue is light exposure, such as sunrise and sunset, which keeps the circadian system regulated within our 24-hour day. Light entering the eyes is detected by the master circadian clock in the brain, which coordinates many bodily functions, including the functions that prepare the body for sleep and wake. For example, the hormone melatonin is released by the pineal gland at night and has been associated with control of the sleep–wake cycle. The detection of light brightness and wavelength allows the master clock to distinguish between the appropriate times for wakefulness and sleep (1).  This is how morning light exposure can help us wake up in preparation for the day. Conversely, darkness signals it is time to sleep and is why we can feel sleepy when in a darker environment. These external cues can be powerful, in that light exposure at different times of the day can shift the circadian system timing and alter sleep patterns (1). While this is helpful for feeling awake during daylight hours, falling asleep can be more of a challenge when the amount of daylight extends into evening hours.

How does DST change our lighting exposure and why does it matter?

With the sudden time change, we experience less light in the mornings. Waking up in the dark can be challenging because our brain will think it is nighttime and signal our bodies to continue sleeping. This could result in feeling groggy and not completely alert when we start our day. Shifting our clock times forward by one hour also means extending daylight into evening hours. When we obtain more exposure to evening light, our brain and circadian system may delay sleep causing us to have more difficulty falling asleep at our normal time. This sudden shift to darker mornings and later evening light exposure may have negative health and safety effects (2). This can include shortened sleep duration, mood disturbances and up to a 30% increased risk for heart attacks (3-7). Fatal traffic accidents have been shown to increase with the transition to DST by 6% in the US, with highest risk in the morning (8). Work-related safety critical events (e.g. near-misses, human-related errors) have also been reported to increase with the time change (9).

What about the slower seasonal change in light availability that occurs naturally?

While DST creates an abrupt change in light and dark exposure, for those of us in the Northern Hemisphere, the march of time towards the summer solstice results in longer daylight hours. With the longer daylight hours, sunlight may shine into a bedroom window earlier than normal, resulting in an earlier wake time. Sunlight extending into the evening hours may make it more difficult to fall asleep in the evening. While the increase in daylight length is gradual, occurring over several months, disruption to sleep can still occur. A recent study of seasonal effects on sleep disruption in the US found that sleep duration decreased with increasing daylight length, and shortest sleep times and earliest wake times occurred during spring (10). Depending on where we are in the US, the number of extra hours of sunshine can vary. Those further north, such as in Alaska, may have close to 24 hours of sunlight on or around the summer solstice. This lack of darkness can make it difficult for the brain to recognize when it is time to sleep. While Alaska may seem like an extreme example, these effects occur to some degree in the lower 48 states as well.

What can we do?

The Centers for Disease Control and Prevention recommends that adults get at least 7 hours of sleep for optimal health and wellbeing (11). However, evidence of disrupted and shortened sleep and adverse health and safety effects following the transition to DST has prompted the call to eliminate seasonal time changes and remain permanently in Standard Time (4, 12). Until that occurs, there are strategies workers and employers can adopt to improve sleep and work safely during DST.

Tips for employers:

• Raise awareness among workers about the health and safety risks associated with the time change and emphasize the need for obtaining adequate sleep.
• Consider reducing any critical or physically/mentally demanding tasks to allow workers time to adjust to the time change, since it can take one week for the body to adapt.

Tips for workers:

• Minimize the effect of DST by adjusting your sleep cycle a few days prior to the time change. The American Academy of Sleep Medicine suggests the following (13):
  • Try to go to bed 15 or 20 minutes earlier each night before the time change. This will give your body a chance to adjust.
  • Begin to transition the timing of other daily routines that are “time cues” for your body.  For example, start eating dinner a little earlier each night or exercising slightly earlier in the morning.
  • On Saturday night, set your clocks ahead one hour in the early evening. Then go to sleep at your normal bedtime.
  • Try to go outside for some early morning sunlight on Sunday.  The bright light will help set your “body clock,” which regulates sleep and alertness.
  • Be mindful of how DST may be affecting your body and be careful when driving or operating machinery if you feel drowsy on Sunday.
  • Stick to your bedtime on Sunday night to get plenty of sleep before the workweek begins on Monday.
• Once you have adapted to DST, try to keep a daily routine time for sleep and waking up to improve sleep and health.
• Keep your sleep environment quiet, comfortable, and cool. Especially during the period of earlier sunrise and later sunsets, using light blocking window coverings can keep sleeping areas dark.

With longer days, comes warmer weather and time to enjoy the sun, but getting enough sleep is also important to ensure worker health and safety.

Imelda Wong, PhD, is an Occupational Hygienist and Epidemiologist with the Division of Science Integration at the National Institute for Occupational Safety and Health. She is also the Coordinator of the Center for Work and Fatigue Research.

Beverly Hittle, PhD, RN, is a post-doctoral fellow with the Division of Science Integration at the National Institute for Occupational Safety and Health. She also is on faculty at the College of Nursing, University of Cincinnati, with expertise in nurse health and safety.

References

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11. Centers for Disease Control and Prevention. How Much Sleep Do I Need? 2017 [Available from: https://www.cdc.gov/sleep/about_sleep/how_much_sleep.html.
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