Our internal body clock (also known as our circadian rhythms) is one of the three major things that influence how well we sleep. This article will teach you all about your circadian rhythms, why they matter, and how to change them if you want to sleep better. The other two underlying mechanisms that you need to learn about for consistently great sleep are your homeostatic pressure and stress levels. If you want to learn tips for changing these aspects, I recommend checking out those articles too.
What Are Circadian Rhythms?
The figure above shows normal circadian rhythms in a human. The word circadian simply means approximately one day, and many things fluctuate in line with these rhythms, including our appetite and how well we perform on cognitive and physical tasks.
Melatonin is closely related to sleep. It usually begins to increase about 2 hours before bedtime to help us fall asleep, and increases its release during the night to help us to remain asleep or get back to sleep when we wake up. Growth hormone spikes during the first half of the night to help promote growth, repair of cells, and restoration of energy for the next day. Body temperature decreases throughout the night, and this drop can help us to fall asleep more comfortably, which is why it can be hard to get to sleep on sweltering nights. Cortisol spikes just after waking in the morning to help increase our arousal levels and get moving for the day. It also tends to drop in the first half of the night to help us sleep more deeply.
How do circadian rhythms work?
We regulate our circadian rhythms through the suprachiasmatic nucleus (SCN) in our brains. We have light/dark receptors in our eyes alongside our cones and rods. The only role of light/dark receptors is to take in the light wavelengths from our environment, and then send these signals to our SCN about what time it probably is based on these light wavelengths. White, blue and green wavelengths have typically signalled the middle of the day, and orange and red wavelengths have indicated that it was either first thing in the morning (dawn and sunrise) or nearly night time (sunset, dusk and campfires).
The role between our light-dark receptors and our SCN worked really well for thousands of years, but then humans invented electricity and lightbulbs, and then TVs and now bright LED screens for smartphones, tablets and computers. Suddenly this super trusty relationship wasn’t so trustworthy anymore. The light/dark receptors began picking up blue wavelengths of light from all these devices first thing in the morning or last thing at night, and our poor SCN found it very difficult to know what time of the day it actually was. As shown in the graph above, the SCN would receive bright (and blue) light cues at night, and tell the pineal gland not to produce melatonin yet, because it must still be daytime.
Researchers have only relatively recently begun to understand the full negative impact that inappropriate exposure to bright light at night can have, especially blue wavelengths of light. In June 2019, the IARC (International Agency for Cancer) classified night shift work in Group 2A, which indicates that it is a probable carcinogen to humans. This is because of the negative impact of trying to sleep and work at different times to most people’s internal circadian rhythms. Remember, our SCN not only helps to regulate our sleep/wake cycle but also how we feel, how we think and how we behave. It influences our appetite, our hormones, our body temperature, our blood pressure, our blood glucose levels and more, so it’s not something that you want to mess around with if you can help it.
Light exposure, either too early in the morning or too late at night, can lead to two big problems. Our internal body clock begins to stop working as well (circadian disruption) or our body clock keeps working, but much later than we want it to (circadian delay).
How Can Knowing This Help Me To Sleep Better?
When all of our circadian rhythm variables are in-sync with our social and working routines, it becomes much easier to make the transition to sleep at night, to wake up in the morning, and to function well during the day.
The ideal time to sleep based on circadian rhythms varies for each person. Between 10:30 pm and 6:30 am is common in many countries. Problems arise when people disregard their circadian rhythms, and try to sleep at different times for social reasons, such as going out late at night with friends or staying up late with their partner. People may also have to sleep at different times for technical reasons, such as rotating shift workers and night-shift workers.
Individuals that are “morning people” tend to have an advanced circadian rhythm, and may sleep best when they go to bed early and wake up early. If they go to bed at 9:00 pm and wake up at 5:00 am every day they feel great, but they struggle to stay up late at night or sleep in later in the morning. Conversely, individuals that are “evening people” tend to have a delayed circadian rhythm, and may sleep best when they go to bed late and wake up late. If they go to bed at 1:00 am and wake up at 9:00 am, they feel great, but struggle to get to sleep earlier than that or wake up at earlier times in the morning. I was like this back when I was in my teens and 20s, and it is more common for people during their adolescence.
Most people’s internal body clocks do shift forward a little bit as they get older, and you would benefit from adjusting your sleep schedule to these new ideal times if this has happened to you. I now generally sleep between 10:30 pm and 6:30 am, but 11:00 pm to 7:00 am is probably suitable for me. I need to get up a bit earlier for work, however, so I use some of the tips below to help bring my internal body clock forward a bit.
If you are a morning person that goes out until 1:00 am, remember that your circadian rhythms will still be trying to wake you up at your usual rise time of 5:00 am. Any sleep that you get after this time will be inferior quality than usual. Likewise, if you are an evening person that wakes up at 6:00 am for work, your body is still going to want you to sleep until 9:00 am, so there’s a good chance that you’ll be quite tired and perform at a lower level until after 9:00 am.
Individuals with chronic insomnia are often not aware of what their natural circadian rhythm is. They tend to make their problem worse by trying to sleep when their body is trying to keep them awake and trying to stay awake when their body is trying to help them to sleep.
If you want to sleep well, try to tune into when your body is feeling sleepy rather than just tired. If your homeostatic sleep pressure is high, you will feel tired and not feel like doing too much. However, this does not mean that you are necessarily ready for sleep. If you feel sleepy, this is a better predictor that you are prepared for sleep and are likely to fall asleep quickly once you go to bed.
Good indicators of sleepiness include regular yawning, your eyes feeling heavier or blinking more slowly, your body feeling heavier and sinking more into your chair, or missing parts of a TV show that you are watching. If you are driving and you notice these signs, you need a power nap, so pull over as quickly as you can, as long as it is safe, and have a short nap before continuing to drive. If it is happening around your usual bedtime, do not try to fight it, get up, and go to bed. It will make it easier for you to fall asleep quickly once you are in bed.
How can you figure out your ideal sleep times?
If you are not sure what your ideal bedtime is, or you tend to feel sleepy at different times from day to day, ask yourself the following question:
If you were on holidays for two weeks and had no commitments that would force you to go to bed or wake up at a particular time, what 8-hour period in a 24-hour cycle would lead to the best sleep for you?
- 8:00 pm to 4:00 am?
- 9:00 pm to 5:00 am?
- 10:00 pm to 6:00 am?
- 11:00 pm to 7:00 am?
- 12:00 midnight to 8:00 am?
- 1:00 am to 9:00 am?
- 2:00 am to 10:00 am?
- 3:00 am to 11:00 am?
Your answer to this question is likely to be your current best bedtime and rise-time based on your circadian rhythms or internal body clock. If you are still not sure, find and complete the morningness-eveningness questionnaire (MEQ) online. It can help you to identify if you have an advanced circadian phase (colloquially known as a “lark”) and should aim to go to bed and wake up earlier than most people. If this is you, try to go to bed to begin between 9:00 pm and 10:00 pm as long as you feel sleepy and set your alarm to get up 8 hours later.
The morningness-eveningness questionnaire can also help you to identify if you have a delayed circadian phase (colloquially known as a “night owl”) and should aim to go to bed and wake up later than most people. If this is you, try to go to bed between midnight and 1:00 am initially as long as you feel sleepy and set your alarm to wake up 8 hours later.
If you are neither a lark nor a night owl, aim to go to bed around 10:30-11:00 pm as long as you feel sleepy and set your alarm to get up 8 hours later. By tuning into signs of sleepiness around these times, you should find where your natural circadian rhythm is, and this will help you to fall asleep faster, stay asleep longer, and have better quality sleep.
There are a few other ways that we can determine what the optimal times are for us to go to bed based on our internal body clock. We can monitor our sleep for 1-2 weeks using a sleep diary or sleep-tracking device and then look at your average to-bed time and average rise time across this period. Then aim to go to stick to these bedtimes and wake times as closely as possible over the next two weeks, and continue to monitor your sleep. If it helps you to get to sleep more quickly, improves your sleep quality, and you feel better and function better during the day, you are definitely on the right track.
The most accurate and scientific way to determine your natural circadian rhythm timing and optimal sleep times are by analysing your dim light melatonin onset (DLMO). Your DLMO can be collected at specific sleep laboratories and in sleep research looking at the impact of light exposure or melatonin tablets. You get your saliva taken at several periods across a night as you sit in a very dimly lit room. The researchers put saliva into test tubes and then sent away for analysis. Your melatonin onset is then determined. The only problem is that you cannot obtain the results immediately, and our circadian rhythms are sensitive to certain factors in the environment, especially light. Therefore, by the time you get your results back in a few weeks, your DLMO may have already shifted, and your ideal bedtimes may have moved too. I, therefore, wouldn’t recommend doing a DLMO test until doctors or researchers can give us our results within 24 hours.
How do we deliberately shift our internal body clock or circadian rhythms if they are different to when we would ideally like to wake and sleep?
Circadian rhythms do tend to stay relatively constant from day-to-day. Still, things that can shift the timing of our internal body clock include light exposure, melatonin supplements or medication, and to a lesser degree, what we eat and when we eat. If your ideal sleep times based on your circadian rhythms are different to your usual sleep times based on your current work schedule and lifestyle, there are specific things that you can do to change it.
If you want to advance your circadian phase and go to sleep earlier at night or get out of bed earlier in the morning, try the following:
- Get as much light exposure as you can shortly after waking in the morning.
- Even 20-30 minutes of being outside in natural light in the morning can make a big difference in helping you to feel alert during the day, as it signals to your brain that the day has begun and helps to switch off melatonin production and release.
- If you combine sunlight exposure with some exercise each morning, your mood is likely to improve too, as regular exercise can be as effective as an antidepressant for depressive symptoms.
- Morning light exposure shortly after you awaken also helps to bring forward the timing of your melatonin onset the following night. It will help you to feel sleepy earlier, as long as you do not get too much light exposure in the evening and before bed.
- Inside light doesn’t have as much lux as natural light, but looking at computer screens, tablets or phones or sitting by a window in the morning may give you some benefit if it is too cold outside or not possible to get outside each day.
- If you have delayed sleep phase disorder, seasonal affective disorder or cannot spare the time to get regular morning sunlight, it may be worth buying Re-timer glasses. They cost a little bit, but you can just put them on as soon as you wake up and wear them for 30 minutes while you get ready for your day and eat some breakfast. The blue-light from this will help you to feel more alert during the day, may improve your mood and should bring your circadian rhythms forward a bit for the following night.
- Minimise light exposure after sunset.
- Our melatonin onset is usually two hours before we typically fall asleep. Light exposure to our eyes, especially blue wavelengths around or after this time suppresses our melatonin production. This can lead to a later sleep onset time, reduced sleep quality and less total sleep time.
- Smartphones, tablets and computers all emit a lot of blue light from their screens, and they are often pretty close to our eyes, which means they can suppress melatonin quite a lot. If you can stay off them in the last two hours before bed and do not use them in bed, this is ideal.
- If you want to use bright screens in the last two hours before bed or in bed, try to change the light that they emit so that it is dimmer and warmer. If you have done this successfully, it will make the screen look orange or red in comparison to usual. On the iPhone, it is called night shift and can be turned on through going to Settings > Display and Brightness and clicking on Night Shift. Mine changes from Sunset to Sunrise. On the computer, there is a free plugin that you can download called f.lux. It also makes the screen a warmer colour from sunrise to sunset or for whichever hours you choose.
- If you like to watch TV at night, this can suppress melatonin onset. The bigger the screen is and the closer it is to you, the more it will affect your circadian rhythms and sleep. To offset this, wear blue-light blocking glasses if you want to watch TV in the two hours before bed. Optometrists can make fancy personalised glasses for you, or you can buy cheaper ones as I did, which block out all of the blue wavelengths of light. UVEX is the brand that I purchased online, and they are inexpensive and effective.
- Recent research coming out of the Monash Sleep & Chronobiology Research Team even suggests that the lights we have in our house can delay our melatonin onset and suppress how much our brain releases. Phillips Hue Smart Lights aim to solve this problem by also changing to warmer colours after sunset, potentially making it easier to feel sleepier earlier and sleep better and longer at night. I have not tried these yet. Wearing blue light blocking glasses around the house would also have a similar effect for a lower price.
- Take melatonin tablets at least two hours before you go to bed.
- Most young, healthy people produce enough melatonin internally, so taking more melatonin will not necessarily help you sleep better, especially if you are minimising your evening light exposure.
- If you have a delayed circadian phase, taking melatonin earlier in the evening can help you to bring your body clock forward and go to bed sooner so that you can wake up earlier the next day.
- Melatonin is available over the counter in the US, but you need a prescription from your GP in Australia, so talk to your doctor about if this is a suitable medication for you and the best times for you to take it.
- If you are sleeping at 1:00 am, but want to sleep at 11:00 pm, first try taking your melatonin at 10:45 pm. By consuming melatonin at this time, it may help you to get to sleep by 12:45 am. Get up no later than 8:45 am the next morning. After a few (2-3) days, take your melatonin tablets at 10:30 pm. It may help you to get to sleep by 12:30 am. Get up no later than 8:30 am the next morning. Keep taking the melatonin tablets 15 minutes earlier every few days and getting up 15 minutes earlier in the morning every few days until you consume melatonin at 9:00 pm, sleep by 11:00 pm, and arise from bed at 7:00 am.
- If you have jet lag and are not feeling sleepy until too late at night, taking melatonin and getting light exposure at the right time can help shift your body clock forward by about 1 hour every night. The phone app ‘Jetlag Genie’ can tell you the best times to do this depending on where you are travelling.
- Deliberately get up at your desired wake-time, seven days a week, no matter what.
- This strategy is hard, as it is fighting against your natural circadian rhythm instead of working with it, but if you are naturally waking up at 9:00 am but want to wake up at 7:00 am, set your alarm for 7:00 am and keep this wake time every day. Because you will not be getting enough sleep, your homeostatic sleep pressure will increase over the subsequent days and help make it easier to fall asleep before what is natural for your circadian rhythms. However, if you do this alongside getting morning sunlight and minimising light exposure after sunset, it is likely to bring your body clock forward too. You might feel tired and struggle to function during the day until your internal body clock shifts forward to your new routine.
- Eat breakfast, lunch and especially dinner earlier than you usually do.
- Our circadian rhythms do respond a little bit to the timing of when we eat. If you eat earlier than usual, it may help you to feel sleepy before you usually do. Some foods are also natural sources of melatonin, such as cherries. However, do not overly focus on what you eat if you want to bring your body clock forward, and try not to overeat too close to your usual bedtime.
It is generally easier to delay our body clock than advance it, especially if you have travelled around the world and have jet lag, which is when your circadian rhythms are out-of-sync with the time in your new environment. While we can realistically advance our body clock by an hour each night with appropriately timed light exposure and melatonin administration, we can delay it up to two hours each night. This means that it is harder to fall asleep earlier than you usually do, and easier to go to sleep later than usual.
If you want to delay your circadian phase and go to sleep (at night) and get out of bed (in the morning) later than you usually do, try the following:
- Seek less sunlight in the morning.
- If you have to go outside before noon, wear sunglasses. If you use your phone, tablet or computer before noon, put on f.lux or night shift to change the colour of your screens to orange or red. If watching TV in the morning, put on blue-light blocking glasses, and use blinds to reduce the light coming into the house.
- Seek more sunlight or blue-light exposure in the afternoon, early evening, and before bed.
- Go outside without sunglasses on in the afternoon. Or turn on plenty of lights in your house in the afternoon and evening. Lastly, watch TV, or play on your phone, tablet or computer before bed. It will help you to stay up later but may lead to less sleep and worse sleep quality.
- Force yourself to stay up later each night.
- The increased sleep pressure when you go to bed may help you to sleep in later the next morning.
- If you do have jetlag, follow the advice of when to get light exposure from apps such as ‘Jetlag Genie’ or ‘Jetlag Rooster’.
- If you have Re-timer glasses, putting these on at the designated times that you need to seek light exposure can help.
- Take melatonin at a specified time.
- I cannot recommend a time for when to have melatonin if you want to delay your circadian rhythms. Please seek advice from a qualified Sleep Physician about when is the best time for you to take it.
- Eat breakfast, lunch and dinner later than you usually do.
- It may or may not help, but try this if you have tried all the other items already.
I’d love to hear if reading this has taught you anything or helped you to see just how important it is to understand your circadian rhythms if you want to have a consistently good night’s sleep. I’m also interested to hear if you will make any changes to your sleep schedule after reading this, and how much it helps if you do!