How Zeitgeber Time Signals Reset Sleep, Internal Clock

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.

Woman yawning in bed
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Defining 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.


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. These are called melanopsin-containing retinal ganglion cells. They are separate sensors from those that contribute to vision, meaning that they may be preserved among the blind. 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. It is also believed that food intake may affect insulin resistance, and this may have an impact on sleep.

Exercise Schedule

Like your meal schedule, when you exercise can also affect your sleep cycle. It is 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. Sleep may affect body temperature and cortisol levels, which may impact sleep. It may be important to avoid aerobic exercise immediately preceding your normal bedtime.


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 a.m.), which may in part preserve heat loss that would occur with a greater difference between the body and the natural environment. When temperature is controlled and kept constant, such as when a house is kept constantly at 72 degrees regardless of season or time of day, this signal may be lost.

Many people sleep better by keeping the windows open at night. Cooling may also help the transition to sleep and relieve insomnia. A hot shower or bath before bed may aid falling asleep because these bring blood to the surface of the skin, which allows heat to radiate out.

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 get morning sunlight could help get you back on track if your sleep quality if suffering. It is recommended that 15 to 30 minutes of sunlight exposure occur immediately upon awakening to optimize the circadian pattern. In some regions, a lightbox may be necessary in the winter months to stabilize sleep.

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 (especially among night owls)
  • 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
  • Becoming sleepy earlier than desired in the evening or earlier than a conventional bedtime
  • Experiencing functional impairment in the workplace, home, or school

Circadian problems often contribute to insomnia and daytime sleepiness. Shift workers may have enhanced risks associated with these issues, including a higher incidence of colon or breast cancer, weight gain, and other problems.

A Word From Verywell

Talk to your healthcare provider 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. If it does not, further guidance and testing may be necessary to optimize sleep health.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  • 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.
  • Division of Sleep Medicine at Harvard Medical School. (2007, December 18). External Factors that Influence Sleep.

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.