Zeitgeber is German for ‘time giver’. It refers to time cues that your body receives and which it uses for certain processes, like controlling your energy levels and alertness, hunger or sleepiness.
Light is the strongest zeitgeber, as it tells the body when it’s morning (wake time) and night (sleep time). However, there are several more ways our body can use to ‘set up’ its own biological clock.
What is circadian rhythm and how do zeitgebers set it?
Circadian rhythm (daily rhythm), is the body’s internal clock. It controls many processes, like hormone release, productivity, and sleep-wake rhythm.
One part of the brain, called the hypothalamus, contains an area which is considered the ‘master circadian clock’. This master clock is called the suprachiasmatic nucleus (SCN) and it gets time information through neurons which lead to the eyes.
As light hits the eye, special melanopsin-containing neurons receive information about light (these cells are not related to vision) and send it to the SCN. From there, various processes – which make up circadian rhythms – begin. For example, if it gets dark, our brain gets the cue ‘it is late’, and increases melatonin, a hormone that makes us sleepy. The opposite happens in the morning.
If we change time zones, we may find ourselves experiencing jet lag. With light as a zeitgeber, our circadian rhythm will slowly change to adjust the day-night schedule of the new time zone we are in.
Our daily schedule and our routine can play a major role in our sleep schedule. If we read a book or have a glass of milk every night before sleeping, the body will soon adjust to that schedule, making us sleepy at the same time every night.
Irregularities in the schedule mess your circadian rhythm up. It is a good idea to stick to a schedule with as little changes as possible. This is especially important with children – a bedtime routine is a recipe for a good night’s rest.
The main time signals: zeitgebers
Light is the most important zeitgeber. It makes the most solid cue, as the sun rises and sets at about the same time every day. As mentioned before, a group of cells is specialized for giving light cues to our brain. Not being connected to vision, they are able to give light cues even to blind people, as long as they have eyes. After melanopsin and its role were discovered, doctors are less likely to opt for removing the eyeballs of totally blind patients.
However, artificial blue light from screens can trick our brain into thinking it’s daytime, so it behaves accordingly – promotes wakefulness and decreases melatonin. Rooms should be kept dark before bedtime.
In countries with low light intensity in winter, many people suffer from seasonal affective disorder. This is expressed as low energy, depression and delayed sleep onset. It can be treated with ‘light therapy’ in which special light boxes are used to mimic daylight.
Temperature drop speeds up the process of falling asleep. It is highly recommendable to sleep in a cool room (about 64.4°F). Scientists claim that having a warm shower before bed not only helps you fall asleep (because your body loses heat after a shower, preparing you for sleep), but also increases your deep sleep (also known as restorative sleep). So, if you want quality rest, have a nice relaxing shower before bed.
Loud music or noise increase alertness and arouse the brain. Silence is associated with peace and rest, so it is very easy for us to fall asleep when there’s no noise and very difficult when the neighbor is throwing a party.
When we are surrounded by tired people who are yawning and/or about to fall asleep, we may feel a strong urge for sleeping as well. It seems that our social environment can make us relaxed and sleepy.
Having a heavy meal just before bed is generally not recommendable as it can keep you awake and prevent you from having good sleep. Your meals can influence your sleep in a positive way, too. If you have a very light meal a two-three hours before bed every night, especially if coupled with calming tea like chamomile, you will give your body a cue that it’s soon time for bed.
Zeitgebers and age
Young healthy people may not feel the consequences of an untidy schedule, late-night meals or having lights on until late at night. However, children and older adults are more sensitive to zeitgebers. They are more likely to be unable to fall asleep after a heavy meal or if they haven’t had enough sunlight during the day.
- Stephan F. K. The “other” circadian system: food as a Zeitgeber. Journal of Biological Rhythms. https://www.ncbi.nlm.nih.gov/pubmed/12164245 Accessed March 7, 2019.
- Rawashdeh O. and Maronde E. The hormonal Zeitgeber melatonin: role as a circadian modulator in memory processing. Frontiers in Molecular Neuroscience. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3295223/ Accessed March 7, 2019.