What Is a Zeitgeber? Time Signals Reset Internal Clock, Sleep Patterns

Definition of Zeitgeber and How it Relates to Sleep's Circadian Rhythms

Zeitgebers are time signals that can naturally enhance sleep via the circadian rhythms and biologic clock
Zeitgebers are time signals that can naturally enhance sleep via the circadian rhythms and biologic clock. Peter Dazeley/Photographer's Choice/Getty Images

It is possible to reset the body's internal clock by exposure to certain time signals from the environment. What are these zeitgeber time signals and how do these influences reset the internal clock that controls sleep, hormone release, and other processes? Discover how light, temperature, meals, and exercise may play a role and what happens if these signals for the circadian rhythm are lost.

What Is the Definition of Zeitgeber?

From the German for “time giver,” Zeitgeber refers to any external cue that can reset the time-keeping system of organisms.

In humans, the circadian system, or biological clock, is controlled by zeitgebers. The central pacemaker lies in the suprachiasmatic nucleus of the brain's anterior hypothalamus.

Here are a few zeitgebers and how they affect your sleep:

  • Daylight

Light is one of the most important zeitgebers that affects sleep. Light influences your internal clock through light sensitive cells in the retina of the eyes. The cells tell your body when it is nighttime and when it's daytime, which helps to regulate your sleep cycle. Before the invention of the lightbulb, people went to sleep when the sun set and woke up as it rose. But now, exposure to unnatural light late into the night (especially from screens) and a lack of access to natural sunlight if you work in an office, could contribute to difficulty sleeping.

  • Meal Schedule

When you eat at night can also affect how well you sleep. Eating later at night is OK, as long as you eat around the same time every night.

Otherwise, you could have different energy levels at a time when you're normally trying to fall asleep, which could throw off your circadian rhythm.

  • Exercise Schedule

Like your meal schedule, when you exercise can also affect your sleep cycle. It's not so much about when you exercise, but more if your timing is consistent.

If your body is used to exercising every night, but then you change it up and go to an early-morning workout one day, you can expect to notice a change in your sleep.

  • Temperature

There is evidence that a drop in temperature helps to transition the body to sleep. The body temperature also naturally dips towards morning (around 4 AM), which may in part preserve heat loss that would occur with a greater difference between the body and the natural environment. Many people sleep better by keeping the windows open at night. Cooling may also help the transition to sleep and relieve insomnia. When temperature is controlled and kept constant, this signal may be lost.

How Zeitgebers Change Over Time

As you age, your circadian rhythm's sensitivity to time cues may change. That could explain why eating pizza at 2 AM before bed in college didn't seem to affect your quality of sleep, while now even simple changes to your routine seem to have a detrimental effect on your sleep patterns. Regulating your meal and exercise schedule and finding ways to get morning sunlight could help get you back on track if your sleep quality if suffering.

Signs of a Sleep Disorder

If you're constantly tired and your sleep quality is poor all the time, you could have a circadian rhythm sleep disorder. Signs of a sleep disorder include:

  • Having a hard time initiating sleep
  • Struggling to maintain sleep, waking up frequently during the night.
  • Tendency to wake up too early and being unable to go back to sleep.
  • Sleep is nonrestorative or of poor quality.

Talk to your doctor if you suspect you have a sleep disorder. Simple changes that enhance your connection to the natural environment, such as exposure to morning sunlight, may be helpful to regulate your biologic clock and sleep patterns.

Sources:

Adam K. (1980). Dietary Habits And Sleep After Bedtime Food Drinks.SLEEP, 3(1), 47-58.

American Academy of Sleep Medicine. (2008). Circadian Rhythm Sleep Disorders. Retrieved January 22, 2016.

Division of Sleep Medicine at Harvard Medical School. (2007, December 18). External Factors that Influence Sleep. Retrieved January 22, 2016

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