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Daylight savings time ends this Sunday. Maskot/Getty Images
  • Daylight savings time impacts mental and physical health in various ways, including sleep, mood, alertness, and appetite.
  • The body’s circadian rhythm is strongly influenced by light. Seasonal changes can result in sleep disruption and mood changes.
  • To adjust to a new wake and sleep time, experts recommend maintaining a consistent sleep schedule and making the change gradually (5 to 10 minutes later each day until your body syncs up with the new time).

On Sunday, November 5, most Americans will have to turn their clocks back one hour as daylight saving time (DST) ends.

As a result, many people are thinking about how gaining an hour of sleep will affect their health.

Adapting to a new sleep schedule can be challenging, especially in the first week following the end of DST. Whether it’s falling asleep later or waking up earlier, this time change can make the mind and body feel out of sorts.

Changing the clocks not only impacts getting a good night’s rest, it can also influence mood, alertness and appetite.

The body’s internal clock is affected by environmental factors, including light.

“In mammals, including humans, the strongest time signal is light. The system that coordinates our sleep/wake rhythm is the suprachiasmatic nucleus which is in the anterior hypothalamus which is directly above the optic chiasm,” said Dr. Sara Benjamin, a clinical associate with Johns Hopkins School of Medicine, Department of Neurology and a part-time instructor in neurology.

Benjamin added: “This system receives light input from photosensitive retinal ganglion cells and then sends signals to other regions of the hypothalamus to regulate the timing of different body systems, including when different hormones are released, when we want to eat, and when to sleep or be awake. Light is one factor that influences our internal clocks, there is also a genetic factor that influences if we tend to be ‘night owls’ or ‘larks.’”

Human beings live in a 24-hour rhythm with alternating light and dark cycles.

We have a pacemaker (the suprachiasmatic nucleus) that regulates circadian rhythms in the brain and maintains a 24-hour cycle through a pathway involving the retina (back of eye) that is sensitive to light and dark, Dr. Nancy Foldvary-Schaefer, DO, MS, Director of the Sleep Disorders Center in Cleveland Clinic’s Neurological Institute, explained.

Light stimulates wakefulness and dark stimulates sleep pathways and the release of melatonin, which is an endogenous hormone that promotes sleep.

The change in seasons impacts mental and physical health.

“Seasons bring changes in light and temperature that affect activity levels and mood,” said Foldvary-Schaefer. “In the realm of sleep and brain function, shorter, darker and colder days tend to bring more sadness and can worsen depression.”

Physically, this also can lead to more daytime sleepiness and fatigue, major symptoms of sleep disorders. People with insomnia and hypersomnia feel better in the summer months. Sunlight also stimulates vitamin D production, which is important for immunity, Foldvary-Schaefer stated.

It’s also important to look at this from a circadian perspective. Circadian misalignment can cause changes in sleep, cognition, mood, metabolism, immune health, cardiac function, and muscle strength to name a few.

“Summer is a time of bright daytime light and outdoor activities; this increases exposure to daytime light and promotes robust circadian alignment,” said Dr. Melissa Knauert, associate professor of pulmonary medicine at Yale School of Medicine. “Winter is a time of more limited daytime light and indoor activities which exacerbate the loss of exposure to daytime light; this loss of light weakens the circadian system’s alignment and thus contributes to dysfunction at the organ level.”

When the clocks turn back, some people feel better and some people feel worse.

“Everyone has an individual sleep need and circadian predilection (normal phase vs. advanced – larks, vs. delayed – night owls),” said Foldvary-Schaefer. “Both factors as well as the state of a person’s sleep health will affect how we react to time changes.”

Nearly 50% of Americans are chronically sleep deprived.

When the time falls back, we gain an hour of sleep, which is helpful for most people and therefore not disruptive. We see more dysfunction in the spring when we add an hour of sleep loss to a chronically sleep-deprived state, Foldvary-Schaefer explained.

Interestingly, studies show that car accidents increase on the Monday after the spring change, but usually decrease on the Monday after the fall time change.

Shift workers face their own challenges, as their wake time is often against the human condition, making time shifts an added challenge, Foldvary-Schaefer noted.

“Most people adapt better to the ‘fall back’ to standard time than they do to daylight savings time, although they like having more daylight in the evening for evening activities,” said Benjamin. “They get an extra hour of sleep with this time change and there is lighter in the morning which is helpful for people to be more alert in the morning.”

Still, with either time change, there can be an uptick in sleep disruption and mood changes. Some people may be less inclined to go back out after work if it is dark, for example, and that may impact mood as they have changes in social interactions, Benjamin explained.

Standard time aligns with most people’s circadian rhythm much better than daylight savings time (agreement between clock/sun time and natural rhythms) so many people sleep less during daylight savings time. They may stay up later due to more hours of light and have more trouble waking up at the desired time for work and school, Benjamin added.

For those who are negatively affected by daylight savings, there are several ways to make the transition as smooth as possible.

When the days are shorter, some people leave for work in the dark and return in the dark. If that is the case, there can be mood-boosting benefits to exposure to natural light during the workday—sitting near a window at lunch or going outside for a short walk when possible, Benjamin stated.

“The spring transition to daylight savings time means it is darker in the morning, so they may need to allow extra time to make sure that they are alert in the morning before driving, for example exercising at home,” said Benjamin. “If people have trouble falling asleep in the evening, especially people who need an early bedtime due to an early wake time for work, we suggest wearing sunglasses when going outside in the evening.”

Promoting overall sleep health is one of the best ways to build resilience to the changes between standard and daylight savings time, according to Knauert.

This includes key strategies such as sleeping at least 7 hours per night and maintaining a consistent sleep schedule throughout the week (e.g., on work days and non-work days). To feel better when making switches from one time to another, the key is to make the switch gradually.

During the fall switch you are asking your body to adjust later, Knauert explained. Therefore, in the week leading up to the switch going to sleep 5 to 10 minutes later each day will gradually accomplish the one hour change that your body clock needs to make.

For example, if your normal bedtime is 10:00PM, you would gradually move your bedtime to 11:00PM in the week leading up to the fallback switch. When fallback occurs, 11:00PM (your body’s new bedtime) becomes 10:00PM and you are back to your normal bedtime. Similarly, in the spring, going to bed 5 to 10 minutes earlier each day is beneficial, Knauert added.

The end of daylight saving time can result in numerous health changes, most notably disruptions in sleep and mood.

Humans have a circadian rhythm that is directly impacted by light. When the seasons change, it can take time for the body to adjust.

To adapt to changing the clocks, experts suggest a regular sleep schedule and going to sleep a few minutes later each night to compensate for the hour difference.