32+ Zeitgebers (Biological Cues) And How To Enhance Your Circadian Rhythm
Right now as I write this, I am watching the morning sun, sitting on a bench in Dolores Park with my shirt off (in 50ºF weather), and typing on my laptop.
Last night, I had no sleep as I just traveled from FL to CA and helping my brother pack until 4am… and I woke up around 5am (8am my normal time… thanks jetlag).
That’s why I believe today’s topic of discussion should be circadian rhythm cues, also called Zeitgebers.
Zeitgebers (the German word for “time givers”) are signals that help synchronize the body's circadian clock with the environment.
In this post, we will discuss the most common zeitgebers, how they affect our circadian rhythm, and how we can use them to enhance our sleep, stress, weight, social life, and more.
What Are Zeitgebers?
Circadian rhythms are necessary for multiple aspects of your daily routine. R
They are driven by internal processes, which are self-sustaining, but highly rely upon circadian time cues (called zeitgebers) to remain appropriately attuned to your environment and desired routine. R
Zeitbergers are environmental cues that help your body sync with Earth’s 24hr light/dark cycle (and 12-month cycle). R
A study at Harvard was able to determine our bodies prefer around a 24 hour day (24 hours and 11 minutes ± 16 minutes), so using zeitbergers are important for chronobiology (biological rhythms). R
Biggest Takeaways (TLDR)
Too Long, Didn’t Read (TLDR) - The 3 biggest takeaways from this post are:
Be consistent in your daily routines
Be active and eat during the daylight hours
When it’s dark outside go to sleep and don’t eat
More takeaways are discussed in the section below about Ways To Hack Zeitbeger Circadian Cues.
Benefits Of Keeping A Circadian Rhythm
Other benefits include:
Higher social activity (more energy) R
Improved Cognitive Performance - serial search, verbal reasoning, working memory tasks, suppressing wrong answers, and manual dexterity R
IMPORTANT - If your circadian cues are not synced between organs, disease can happen. R
List Of Zeitgebers And Circadian Cues
1. Light Intensity
Light is the most powerful zeitberger and it essentially tells us when to go to sleep and when wake. R
An example of this is sleeping in the dark and being active during light hours. R
Light is able to activate the Suprachiasmatic Nucleus (SCN), which is our brain’s internal pacemaker, thus starting our day. R
Lack of light can decrease your mood and energy levels, as seen in patients with Seasonal Affective Disorder (SAD) during winter months up north. R
On the opposite spectrum, too much light may keep you awake and disrupt your natural signals to go to sleep. R
For example, in animal models, constant light has shown to affect lactation and cause dysregulation of hormones - VIP, AVP, and PER1 in the SCN. R
It’s important to note that light also works without the need of photoreceptors, as blind can still have their circadian rhythm affected by light. R
TLDR - Get bright light during the morning/day and reduce light intensity in the evening.
2. Sunlight And Moonlight
TLDR - Follow sunlight patterns in your area to keep a proper circadian rhythm.
3. Light Spectrum (Artificial And Blue Light vs Red/Purple Light)
TLDR - Get all wavelengths of light during the day, lots of red light in the evening and block out blue at night.
Exercise sessions can induce phase shifts in circadian rhythm as exercise is a strong zeigeber (independent of light). R
Depending on the time of day, exercise can enhance certain biological functions. R
For example, treadmill exercise (rodent model) in the day or in the evening vs dawn has shown to enhance memory function and synaptic plasticity. R
TLDR - Exercise at the same time every day.
5. Water, Drinks, And Fluid Amount
Another common zeitgeber is water intake, which is dependent on the amount of fluid (more discussed in vasopressin below). R
TLDR - Drink water during the day and make sure to have proper amount of sodium/magnesium in the evening before bed.
6. Food Type And Timing
Food intake is a zeitgeber (talks to the brain via ghrelin, leptin, glucose, insulin, etc) and depending on the time of day you eat, food can affects different pathways and metabolic funcitons. R
For example, mice that were delayed in their eating patterns for 2 days had changes in their liver circadian rhythmicity. R
TLDR - Eat during the day (when it’s light out) and fast at night. R
7. Latitude And Geomagnetism
Moonlight may act as a zeitgeber by it’s gravitational pull and light-dark cycle. R
Your geographical location has an effect on circadian rhythm by latitude and geomagnetism. R
For example, bipolar patients in India had increased episodes of mania at certain latitudinal gradients. R
TLDR - Depending on your location on the globe, you may have different circadian patterns than other parts of the world.
8. Social Interaction
Social interaction can act as a zeitgeber and is strongly enhanced if kept to a regular routine (ie work, school, family dinner, listening to music, etc). R
Low amounts of social interaction have been linked to a bipolar disorder (circadian mismatch is a common phenomenon in BD). R
TLDR - Keep social interaction during the day and keep it routine.
9. Sex And Orgasms
As a social stimuli, routine sex and orgasms (as studied with rodents ejaculating) may act as a zeitgeber. R
TLDR - Have sex around the same time every day.
10. Heat And Cold
Core body temperature changes throughout the day (independent of light cues). R
Exposing yourself to cold during the day can raise your internal body temperature, thus increasing metabolic rate and fat oxidation (increased Brown Adipose Tissue, BAT). R
TLDR - Start your day off with a cold shower, then keep (relatively) warmer during the day and colder at night.
11. Gender And Age
Gender and age may play an important role in how zeitgeber’s affect us individually. R
For example, being a night-owl vs morning-person may be influence not only by genetics but also by age and sex. R
TLDR - You may be more susceptible to circadian changes if you are a young woman.
12. Cognitive Performance
TLDR - Learn during the day and don’t stimulate your brain cognitively in the evening.
13. Fear And Stress
Fear and stress can act as a zeitgeber (independent of light). R
Emotional states, such as fear, anxiety, and depression, can disrupt circadian rhythms. R
These stressors can affect ACTH and cause phase shifts the adrenal clock as well as the HPA axis. R
TLDR - Use destress techniques to protect against circadian rhythm disruptions.
Cortisol acts as a zeitgeber-hormone that entrains activities such as metabolism, immune function, and cardiovascular activity. R
Taking steroids or having inflammation may throw cortisol’s cue out of line. R
Being under constant stress can also mess up your circadian rhythm. R
In animal models, having high hypothalamic glucocorticoid levels (incl cortisol and AGRP) has shown to cause obesity. R
TLDR - Stress yourself (with exercise and sunlight) in the morning and day and refrain from stress in the evening.
TLDR - Refrain from alcohol intake.
Nicotinic alpha-9 acetylcholine receptor subunit (alpha-9 nAChR) participate in retinal signaling processes responsible of the positive masking of sleep by light. R
TLDR - As a stimulant, nicotine can program your circadian rhythm.
TLDR - The metabolite KYNA changes throughout the day and affects memory formation.
TLDR - Use coffee to wake yourself up a few hours after getting up.
Leptin may act as a zeitgeber by affecting energy levels (via hypothalamus). R
TLDR - Leptin as a satiety hormone should be kept at healthy levels to help you maintain a proper circadian rhythm.
21. Insulin And Glucose
Insulin and glucose are controlled by the SCN and act as zeitgeber cues. R
TLDR - Refrain from insulin resistance by not eating after dark.
Vasopressin (ADH) is expressed in the brain, blood, and retinal cells and is reactive to light cues by the SCN. R
ADH controls multiple mechanisms such as water intake, fluid retention, and memory. R
The changes in ADH throughout the day give you the feeling of needing to drink water before bed. R
TLDR - Get light in your eyes in the morning, but not at night.
23. Nitric Oxide
TLDR - Do things such as eat greens or go into the sun during the day, and refrain from it in the evening.
24. Insulin-Like Growth Factor-1 (IGF-1)
Insulin-Like Growth Factor-1 (IGF-1) functions as a zeitgeber for cellular hypothalamic circadian clocks (via GSK-3β/BMAL-1). R
If IGF-1 get off it’s circadian rhythm, cancer can occur. R
TLDR - Exercise in the day and eat carbs in the evening.
25. Activation And Detoxification
For example, Peroxisome Proliferator-Activated Receptor gamma (Ppar-γ) acts as a circadian rhythm of Cytochrome P450 2a6 (CYP2A6). R
TLDR - Remove toxins from your routine as they can mess up your circadian rhythm (read biotoxin accumulation post).
Orexin (hypocretin) acts as a zeitgeber affecting sleep, feeding, stress, anxiety, energy levels, reward, and motivation. R
Histamine is a master neurotransmitter that has a circadian rhythm and acts as a zeitgeber. R
Higher levels of histamine in the morning and day can improve cognition and wakefulness, while reducing histamine in the evening (in the brain) can help you sleep. R
While having high levels of histamine acting on H1 and H2 receptors may cause immune responses (such as Histamine Intolerance), having higher histamine on the H3 receptor may be key to improving cognition. R
TLDR - Increase histamine in the brain during the day and reduce it at night.
By acting on the SCN, Serotonin (5-HT) may act as a zeitgeber in response to light. R
This may be why 5-HT is useful in treating sleep and circadian disorders. R
TLDR - Serotonin modulators affect your circadian rhythm.
29. Melanin-Concentrating hormone (MCH)
Melanin-concentrating hormone (MCH) acts as neuromodulator in the lateral hypothalamus and incerto-hypothalamic area. R
MCH fluctuations may help entrain normal circadian rhythms. R
Those who are sleep deprived are may have significantly higher levels of MCH is cerebrospinal fluid (as seen in animal models). R
TLDR - Sleep at the same time everyday.
30. Vagal Stimulations
Apart from proper food timing, the vagus nerve may play a role as a circadian cue. R
For example, chronic intake of a high fat diet without day-specific cues can impair vagal tone. R
TLDR - Keep a healthy vagus nerve (meditation, proper food timing, singing in cold showers, etc).
The neurotransmitter adenosine acts as a zeitgeber. R
Adenosine builds up though-out the day and enough of it can make us feel sleepy. R
Reverb-a is haem (iron-containing compound in blood) and thus iron may act as a zeitgeber. R
For example, Rev-erb-a and ROR form a secondary circadian loop that interacts with the primary negative feedback loop of CLOCK/ARNTL and PERs/CRYs in which Rev-erb-a represses the expression of ARNTL, whereas ROR stimulates expression. R
TLDR - Healthy iron blood levels are necessary for a good circadian rhythm.
What Can Disrupt Your Circadian Rhythm?
What Happens If You Ignore Zeitgebers?
Some possible downsides to ignoring zeitgebers/your circadian rhythm may include (from acute or chronic ignorance):
Hormone Imbalances - cortisol flip-flop, insulin resistance, leptin resistance, etc R
Immune Dysfunction R
Increased susceptibility to viral infections R
Intestinal Permeability (Leaky Gut) R
Mitochondrial Dysfunction R
Seasonal Affective Disorder R
Sleeping With A Partner
Biohacks And Supplements To Enhance Your Circadian Rhythm
It is important that you keep a consistent daily routine so your zeitbegers are rock solid.
Take a cold shower right after waking up to increase your metabolic rate.
Use a bright light device in the morning
Eat protein and fats in the morning
Exercise (cardio) in the morning 2-4 hours after waking in sunlight
Eat high protein and fats during the day
Be socially active during the day
Exercise (strength) in the afternoon (4-7pm) in sunlight
Eat higher amount of carb-rich foods (low glycemic, such as resistant starches) for dinner (3-4hrs before bed)
Watch the sunset
Do not eat after sunset
Sauna (if available)
Wear red glasses
Do not do anything cognitively stimulating
Take hot shower before bed (body temperature)
Take glycine after shower (body temperature)
Participate in intimacy (or orgasm) before sleep (as routine)
Take sublingual melatonin
Sleep in cold room (below 76º)
Other Things To Note:
If you choose to use hormetic tools, do your regular amounts in the morning/noon but if you want to use it in the evening, do a little bit extra as the oxidative stress can make you tired - for example HBOT or sauna.
Some stimulants may be okay for some in the morning - ie Modafinil, H3R antagonists, amphetamines, etc, but for others depending on their metabolism may do poorly with them.
Sleep drugs aren’t really recommended although suvorexant or agomelatine may be useful for some, but alcohol really isn’t recommended for sleep.
Supplements That Help With Zeitgebers And Circadian Rhythms
Mechanism Of Action
Carbon monoxide may help with preserving circadian genes in brain. R