Have you ever noticed that you feel awake when it’s light outside but sleepy when it’s dark? Our body knows from our circadian rhythm that it needs to get up in the morning and go to bed at night. Circadian rhythms, also known as internal clocks, control important bodily processes, letting you know when you are hungry, thirsty, and sleepy.
These clocks are present in all living things (even bacteria!). You can cycle for a day, but also for a longer period. Maternity rhythms, for example, maintains a schedule that spans 365 days. These longer rhythms are most visible in spring and winter when you see tulips in bloom, bears hibernate, or birds migrating. Our genes and environmental cues such as light, temperature, food or stress influence our internal clock.
The way your body feels and behaves changes throughout the day and every year. Our daily changes are due to circadian rhythms. An internal 24-hour clock set by a combination of genes and environment that cycles through bodily processes daily. Our annual changes can be traced back to approximately annual rhythms.
A 365-day internal clock set by a combination of genes and environment that annually cycles through physical and behavioural processes such as hibernation. These rhythms, also known as our internal clocks, keep time by following changes in our environment. Changes include annual temperature changes or daily changes in light conditions. Thanks to these environmental signals, our internal clock can determine whether we are feeling awake, tired, hungry, or sad). If we didn’t have these internal clocks, we wouldn’t be feeling the right things at the right times.
For example, if you don’t feel tired at night, you probably wouldn’t go to bed. This would be bad for your health as your brain doesn’t get the rest it needs to function properly. Rhythms of life, internal clocks that run all year round also influence physical processes that we are not even aware of. This can include how we digest our meals and break down food into nutrients and energy.
WHAT ARE CIRCADIAN RHYTHMS?
Circadian Rhythms are physical, mental, and behavioural changes that follow a 24-hour cycle. These natural processes respond primarily to light and darkness and affect most living things, including animals, plants, and microbes. Chronobiology is the study of circadian rhythms. An example of a light-related circadian rhythm is sleeping at night and being awake during the day. The picture of the average adolescent circadian cycle shows the typical adolescent circadian rhythm cycle.
WHAT IS THE MASTER CLOCK?
A master clock in the brain coordinates all the biological clocks in a living being and keeps the clocks in sync. In vertebrates, including humans, the master clock is a group of approximately 20,000 nerve cells (neurons) that form a structure called the suprachiasmatic nucleus, or SCN. Located in a part of the brain called the hypothalamus, the SCN receives information directly from the eyes.
WHAT MAKES THE BODILY CLOCK UP?
Our daily internal clocks are controlled by genes passed from our parents. These genes contain the code for making proteins, molecules in the body that perform specific tasks. Some of the genes that control our internal clocks produce proteins called “activator proteins,” which bind to a gene to turn it on. Sometimes activators can only bind to a gene after they have bound to each other (as in our internal clocks).’ and others produce proteins called ‘suppressor proteins’ which serve to turn off a process, either by binding directly to a gene or by preventing activators from binding to the gene (as in our internal clocks).
Activators are proteins that turn on a gene while suppressors are proteins that turn off a gene. In our daily internal clock, we need two triggers that match to turn on a gene. This gene is normally activated in the morning. Once this gene is activated, many different proteins are made, including the two suppressors. When many of these suppressor proteins are being produced, we usually feel energized and optimistic! As the day progresses, the concentration of these suppressor proteins in our body increases. Enough suppressor proteins are produced at night to block the activators and turn off the gene. While you sleep, blood flow suppressors are broken down. During this breakdown, which occurs during the night, we feel tired and sleepy. Another protein is also produced at night, a protein called “melatonin,” that helps keep our circadian clocks on time. Once the suppressors are completely broken down, the activators are no longer prevented from binding to each other or to the gene, and the cycle repeats.
WHAT ROLE DO CIRCADIAN RHYTHMS PLAY IN HUMAN HEALTH?
Circadian rhythms are essential to human health, and problems can arise when environmental influences mistime our internal clocks. A frequent disturbance of the clock is the use of artificial light technology at night. For example, the light from a tablet or phone screen can mess up our daily clock. Melatonin, the protein that controls our clock genes, is affected by exposure to light. In the dark, our bodies are signalled to produce large amounts of melatonin, making us sleepy and preparing us for bed.
However, we don’t produce much melatonin when exposed to light. The light from our phones can trick our bodies into thinking it’s still daylight, making it harder to fall asleep and making us more tired in the morning. Interestingly, only certain colours of light act as signals to start melatonin production. Light waves with shorter wavelengths, such as violet or blue light, effectively stop melatonin production. By filtering out this blue light with blue-blocking glasses or apps on a phone or tablet, the brain doesn’t get the message to stop producing melatonin and we won’t experience the negative effects of artificial light at night.
Another way we can mess with our internal clock is by not getting enough sleep at night or sleeping during the day. Things like taking a plane to a new time zone or setting our alarm clock too early can throw off our circadian rhythm. Too little sleep leads to well-known problems such as poor concentration, learning difficulties and slower reaction times.
You may also have noticed that after a bad night, you get in a bad mood, feel sadder, or have trouble communicating with the people around you. Disrupting the natural rhythm of our internal clocks can even lead to poor digestion, heart problems, weight gain and a weakened immune system. For example, scientists found that people who didn’t get enough sleep at night had an immune system that produced infection-fighting proteins at the wrong time of day, meaning those proteins weren’t available during actual infection times. However, the scientists also found that their immune systems returned to normal after at least 5 days of 8 hours of continuous sleep.
WHAT ABOUT THE CIRCANNUAL RHYTHMS?
As we have already mentioned, circannual rhythms are like circadian rhythms in that they rhythmically control our bodily processes, but instead of keeping time on a daily scale, circannual clocks operate on a yearly scale. We see evidence of functioning circannual clocks in humans.
As the seasons change, we see a change in our mood and how our bodies digest the food we eat. These changes are believed to be due to melatonin, the same protein that helps us sleep at night. Our bodies produce melatonin when it’s dark outside, so we produce more melatonin in winter when the days are shorter. When it builds up in high levels in the blood, melatonin sends our body at least two different messages: it’s time for bed and to stop breaking down sugar. So, increased melatonin means we feel more tired in the winter and our appetite increases because we can’t convert sugar into energy as easily.
We see many more amazing examples of circannual clocks in nature. For example, when tulips sense spring and start growing through the earth, or when bears sense winter and hibernate. Without annual clocks, a tulip could flower in winter, or a bear wouldn’t hibernate. This would freeze the tulip and starve the bear. How do semi-annual clocks work? Organisms use cues like temperature and daylight to tell the season. For example, tulips (as well as other seasonal flowering plants) use cold exposure and length of daylight to estimate the best time to bloom. After a bulb has been exposed to the cold of winter and recognizes the increase in temperature or length of daylight that spring brings, it knows that this is the best time to bloom. Brown bears use temperature as a hibernation signal: when the temperature drops below 0 °C (32 °F), a bear will enter its den. When the temperature rises above 0°C, bear wakes up and comes out of his den.What if those external cues change over time, which is what may happen with climate change?
Rising temperatures associated with rapid climate change can throw off the circa-annual rhythms of organisms, preventing them from properly timing processes such as hibernation or flowering. Bears can wake up too early or never hibernate! Bird migration is another process that may be affected by rapid climate change. Many bird species use a combination of changes in daylight length, temperature, and precipitation to determine when to begin their migration.
Migratory birds leave behind a breeding ground for warmer climates, allowing them to escape the harsh winter weather and associated scarce food supplies. They then return to the breeding grounds the following spring when the weather improves, and food becomes available again. Unfortunately, warmer temperatures can lead to a mismatch between food abundance or weather conditions and bird movement. For example, if spring comes earlier and the birds cannot adjust their migration, they will come at the wrong time and there will be less food available.
HOW DOES THE CIRCADIAN RHYTHM AFFECT HEALTH?
Circadian rhythms can affect important functions in our body, such as:
- Hormone secretion
- Eating habits and digestion
- Body temperature
However, most people notice the effects of circadian rhythms on their sleep patterns. The SCN controls the production of melatonin, a hormone that causes sleep. It receives information about incoming light from the optic nerves, which carry information from the eyes to the brain. When there’s less light, for example at night, the SCN tells the brain to produce more melatonin to make you feel sleepy.
WHAT FACTORS CAN CHANGE THE CIRCADIAN RHYTHM?
Changes in our bodies and environmental factors can cause our circadian rhythms and natural cycle of light and dark to become out of sync. For example:
- Mutations or changes in certain genes can affect our biological clock.
- Jet lag or shift work causes changes in the light-dark cycle.
Light from electronic devices at night can confuse our biological clocks. These changes can cause trouble sleeping and lead to other chronic health conditions like obesity, diabetes, depression, bipolar disorder, and seasonal affective disorder.
HOW ARE CIRCADIAN RHYTHMS RELATED TO JET LAG?
When you cross different time zones, your biological clock differs from local time. For example, if you fly east from California to New York, you “lose” 3 hours. If you wake up at 7am. On the east coast, your biological clock still runs on west coast time, hence it feels like 4:00 am. m. Your biological clock will be reset, but at a different rate. It usually takes a few days for your biological clock to adjust to a new time zone. Adjusting after “gaining” time can be a little easier than after “losing” time because the brain adapts differently in both situations.
Taken together, the findings indicate that thermoregulatory changes manifested at different phases of the CBT rhythm determine sleep expression. Activating heat loss and suppressing heat production that occurs during the falling phase of the temperature rhythm promotes falling asleep, staying asleep, and deeper sleep. The increased heat production and heat retention that accompanies the rise in temperature promotes arousal.
Our internal clocks are vital to ensure our bodies function normally. These clocks are present in all animals to help them stay alive. Internal clocks help our body control behaviours and bodily processes more efficiently. The next time you feel sleepy, hungry or thirsty; Remember that these feelings are not due to chance, but to your circadian and circannual rhythm.