What is a Zeitgeber?

The Definition of Zeitgeber and How it Relates to Sleep

Woman yawning in bed
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From the German for “time giver,” Zeitgeber refers to any external cue that can rest the time-keeping system of organisms. In humans, the circadian system, or biological clock, is controlled by zeitgebers.

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


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 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 late 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.

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 a.m. 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 see morning light 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 and check out these resources for more information about things that could be messing with your sleep:

Causes of Sleep Disorders

Can Vitamin Deficiency Cause Insomnia?

Pupil Size Can Objectively Identify Sleepiness, Sleep Deprivation

Should You Ban the TV From Your Bedroom to Relieve Insomnia?

What Is Insomnia? The Features, Symptoms, and Causes


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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