What Is Circadian Rhythm?

This is the physiological processes that take place during a 24 period in living organisms, including humans, animals, plants, fungi and cyanobacteria. Most of these “clocks” are internal, and all our organs have their own, individual clocks, but they are often affected by external stimuli from the environment. Patterns of brain activity, sleep, temperature control, hormone production, eating, cell regeneration and other biological processes are all regulated by our circadian rhythms.

This week I am taking a look at two opposing hormones that affect our sleep and waking pattern, cortisol and melatonin, and how we can help to maximise the benefits and minimise influences that may be detrimental to health.


Cortisol is a steroid hormone that is responsible for regulating the metabolism and immune system. It also plays an important part in our stress response.

It is made in the adrenal glands and transported around the body via the bloodstream. The hypothalamus and pituitary gland in the brain sense whether cortisol levels in the blood are correct and if they need adjusting, a signal is sent to the adrenal glands to release more. Every cell in the body has a receptor for cortisol, and the type of cell will determine what effect cortisol will exert on it.

The Many Roles Cortisol Plays Are:

  • Controlling blood sugar levels
  • Influencing stress levels
  • Regulating metabolism
  • Anti-inflammatory
  • Influencing memory formation
  • Regulating salt and water balance
  • Influencing blood pressure
  • Foetal development
  • Influencing circadian rhythm

The levels of cortisol fluctuate during the day but are typically highest first thing in the morning, elevating about 30 minutes to an hour before waking, which will initiate your waking process. They start to fall during the day and should be at their lowest at bedtime. When you experience stress your levels of cortisol rise to help you deal with the stressful situation. In our ancestors time this would have typically been the “fight or flight” response where they needed to react quickly to flee from, or fight against, an enemy or animal. This response puts everything else on the back-burner, sending blood to the muscles in order to be able to activate them to the maximum. Digestion gets put on hold and we are on high alert.

Too Little Cortisol:

This may be due to a functional problem within the pituitary or adrenal glands, which impairs the release of cortisol. This can be a gradual process and so may go un-noticed for a while. Symptoms can include:

  • Fatigue
  • Dizziness (especially when rising to standing)
  • Weight loss
  • Muscle weakness
  • Mood changes
  • Areas of skin darkening

A lack of cortisol can be life threatening and immediate attention should be sought. Addisons disease is a condition of little to no cortisol production and is fatal unless treatment is sought.

Too Much Cortisol:

Cushing’s syndrome is an issue where a nodule or tumour in the pituitary gland can cause the body to produce too much cortisol all the time. Symptoms include:

  • Rapid weight gain – particularly in the face, abdomen and chest
  • Easily bruised skin
  • Muscle weakness
  • Diabetes
  • Flushed skin – particularly the face
  • High blood pressure
  • Mood swings
  • Osteoporosis
  • Loss of libido
  • Menstrual problems such as loss of cycle

The Effects of Chronic Stress

As well as conditions such as Cushing’s syndrome, our modern world often presents us with chronic stress, as opposed to acute stress, and this can cause major problems with a continuous production of cortisol. Because cortisol has such a wide range of influences over the body high amounts can affect your digestive system, reproductive system, immune system and even growth processes. When we face acute stress (short lived) the levels of cortisol go up to help us deal with the problem, but after the episode is over levels go back down to normal and the body’s different systems resume their normal functions. However, chronic stress keeps cortisol levels high, meaning that your body stays in a constant state of alarm. This can create many health issues such as:

  • Anxiety
  • Depression
  • Weight gain
  • Headaches
  • Heart disease
  • Memory and concentration problems
  • Sleep disruption
  • Digestive problems
  • Susceptibility to infections

Obviously we need cortisol, it is part of our normal daily functioning, controlling our sleep/wake cycle and many other health functions. A dysregulated circadian rhythm, resulting in flatter diurnal cortisol levels has been linked to depression in women.

We need some stress in our lives as this helps with hormesis – a dose response reaction and adaptation by the body to an environmental stimulus which, when presented in a low dose stimulation can be beneficial or, conversely, a high dose stimulation can be toxic. Exercise, for example, provides a hormetic stimulation, whereupon the body adapts to the stress by becoming bigger, faster or stronger. Too much exercise, however, can create too much cortisol in the body and therefore impede adaptation rather than promote it.

So how do we help to control our cortisol levels?

  • Sleep – the length, quality and timing of your sleep all affect cortisol levels. Shift workers tend to have an increase in cortisol levels because their circadian rhythm is erratic. Sleep deprivation increases cortisol levels. Exposure to bright lights in the evenings inhibits the release of melatonin, which is required for the brain to start winding down and preparing for sleep and keeps cortisol levels high because the brain is under the impression that it is still daytime. Wearing blue blocking glasses can help by cutting out blue light emitted from screens and light bulbs during the evening. Waking up regularly during the night, or suffering from insomnia, can cause issues with cortisol, particularly if you switch lights on when you get out of bed as the blue light enters through the retina, tricking the brain into thinking it is time to get up, raising the levels of cortisol accordingly.
  • Exercise – exercising during the day as opposed to the evening can help to keep cortisol in balance. Intense exercise increases cortisol immediately after the bout, but levels decrease at night. This increase helps the body to adapt to the stimulus of intense training, promoting muscle growth. Regular training also lessens the amount of cortisol typically released. Mild, or moderate exercise, however, does not increase levels after the workout, but still helps to lower levels at night.
  • Caffeine – avoiding caffeine in the evening can be very helpful as caffeine is an excitatory stimulus that raises cortisol. Many athletes use caffeine as a stimulus to encourage more efficient, and stronger, training sessions.
  • Stress reduction – recognising triggers of stress are important because stressful thoughts release cortisol. Practising mindfulness as a stress reduction technique can help mitigate the effects of cortisol release and pre-empt the feelings of negativity, anxiety and worry. Being aware of what provokes your stress, and practising techniques to accept them and observe them puts you in the driving seat of your thoughts, worries and fears, as opposed to being carried away as a passenger with them, feeling out of control.
  • Relax – relaxation therapies are very helpful to combat stress. Techniques such as deep breathing, body scans, massage, long hot baths, restful music, tai chi have all been shown to reduce stress and decrease cortisol.
  • Pets – taking care of an animal can have a very beneficial effect on stress and cortisol. Therapy dogs are now being used to help reduce stress and anxiety with patients before minor medical procedures or in rehabilitation. It is believed that this is also a two-way relationship as studies have indicated that the pet also benefits from the companionship.
  • Fun – this may sound obvious, but often life gets in the way and we forget to let our hair down and simply enjoy ourselves. Positivity, in and of itself, can help to promote better health, lowering cortisol, reducing cardiovascular disease risk and improving immune function, increasing resistance to infection. Activities and hobbies help to develop life satisfaction and wellbeing. Being outside in nature, spending time with family and friends and finding a hobby that you really love are all great ways of reducing stress and lowering cortisol.
  • Nutrition – food can have a positive or negative effect on the body. Sugar, for instance, triggers cortisol release, with a high intake keeping levels elevated. Higher cortisol and increased visceral adipose tissue in young overweight individuals has been linked to high sugar consumption. However, because “comfort foods” are typically sweet, this can also lead to a temporary decrease in cortisol levels as the individual experiences a brief respite from the stressful feelings. But this is short-lived because the stressful feelings return – and often bring a feeling of guilt or remorse for having “indulged” in the comfort foods.
  • Water – dehydration can lead to an increase in cortisol levels. Whilst this does not mean drinking umpteen glasses of water per day, it simply means being sensible and maintaining hydration according to your needs. If you are exercising heavily you are more likely to need extra water due to sweating, for example, or if you live in a hot country then you will likely need to drink more water than someone who lives in a cold country.
  • Walking – taking a walk first thing in the morning, or even just stepping outside into the morning light, helps to up-regulate cortisol and reaffirm that it is time to be alert and ready to take on the day.


As with the other hormones I have written about this month, one hormone usually works in opposition to another and this is the case with these two. As with cortisol, melatonin is connected to our circadian rhythm, only it rises in the evening and falls in the morning. This means that it is directly connected to our sleep. If we put obstacles in the pathway of melatonin production, or the release of it, then our sleep – and ultimately our health – will be affected. Sleep deprivation is linked to a myriad of health issues – and is actually fatal. Yes – you can die from not sleeping!

Melatonin is made by the pineal gland, which is situated just above the middle of the brain. Exposure to light and dark is a key factor in sleep. A nerve pathway through the retina in the eye leads to the hypothalamus in the brain, where a special signalling centre called the suprachiasmatic nucleus (SCN) sends messages to areas of the brain responsible for controlling hormones, body temperature and other factors that determine whether we are sleepy or not.

Light entering the eye in the morning signals the release of cortisol, as we have seen above, but it also delays the release of melatonin until darkness arrives. The retina in the eye contains a pigment called melanopsin, which changes shape in response to blue light. This then triggers a chemical response that informs the brain about the external environment and causes increases or decreases in cortisol or melatonin, depending on whether the body is perceiving that it is daytime or night-time. You can see, therefore, how artificial light plays a big role in tricking the brain into thinking it is still daytime and thus suppressing the release of melatonin, resulting in sleeping problems.

Melatonin is typically released between 8 and 9pm, making us start to feel tired and less alert, and we naturally want to go to bed. Melatonin stays elevated for about 12 hours, while we are sleeping, or resting, and then lowers between 8 and 9am. During the time that melatonin levels are high our body temperature is reduced and there is some evidence that melatonin stabilises and strengthens circadian rhythms within the body. All our other organs also have their own circadian rhythms and these are dependent on the signal received from melatonin so, for example, homeostasis, glucose regulation, immune function, anti-oxidant defences are all reliant on this message being received. Disruption of melatonin production can result in these pathways being affected and subsequent predisposition to diseases.

A review looked at the effects of disruption of melatonin on health and discovered elevated rates of cancers, diabetes, cardiovascular risks, obesity, mood disorders and age-related macular degeneration. One study that was included in the review looked at nurses working shiftwork and particularly night work, with an association found between sustained nightwork and a 50-100% higher incidence of breast cancer.

Out Of Synch

Unfortunately it is now all too common to be exposed routinely to artificial light at night (ALAN) either at home, at work, or out and about socially. Coupled with this is the reduced exposure to daytime light and sunlight. Vitamin D insufficiency and deficiency are now becoming widespread in both adults and children, particularly in countries where it is colder and darker for much of the year, and with adults spending much of their time indoors working, and children spending more time indoors in front of computer screens and tablets instead of playing outside, this is becoming an epidemic, leading to poor health outcomes in relation to various cancers and psychiatric, hypertensive, cardiac, and vascular diseases of modern civilisation.

Our actions during the hours of daylight also affect our levels of cortisol and melatonin. How many of us don sunglasses in the summer time without batting an eyelid (pun intended!). But are we doing more harm than good? Sure, we want to protect our eyes from the glaring rays of the sun (and maybe look cool at the same time!) but sunglasses prevent the light from entering our eyes during the critical hours that we need to be exposed to UVA and UVB light, as these are the precursors to melatonin production, and therefore this interferes with the signalling that is crucial to telling our body that it is still daytime and to up-regulate cortisol and down-regulate melatonin.

Technology and Melatonin

Studies have shown that women who have a family history of breast cancer, or carry the mutated BRCA1 or BRCA2 gene, should avoid using their smartphones, laptops and tablets at night and/or use blue-blocking glasses with amber lenses to decrease the exposure to blue light before sleep. This is due to the fact that disruption to the circadian rhythm because of suppressed melatonin increases the risk of breast cancer. Similarly, students were monitored using their smartphones at night before bed with, and without, amber blue blocking filtering glasses and the effect on their sleep quality. The authors concluded that “blocking the short-wave component of the light emitted by the smartphones screens improves human sleep”

And, whilst I am not trying to turn this blog into an anti-electronic-devices blog, another study looked at the link between the exposure of human skin cells to the light emitted from electronic devices and the production of reactive oxygen species (ROS), apoptosis and necrosis. And in this age of constant imagery, due to online platforms such as Instagram, frequent exposure to the flashes emitted whilst taking selfies have also been associated with skin damage and accelerated skin ageing.

The take-home message here, I think, is to use your devices with caution, especially at night, using blue blocking glasses and/or the functions within the device to lower the blue light emissions at night-time. I wear my blue blockers every evening to minimise the effect of light emissions from household lightbulbs, the television and when using my computer, phone or iPad – which I try to restrict in the last couple of hours before bed. If you think about it, it makes complete sense; the effect physiologically of melatonin is to lower core body temperature and induce sleepiness, but the effect of light is to raise core temperature and increase alertness and performance – so you can see how this can create issues with both sleep quantity and quality!!

How Does Food Affect Melatonin?

There are foods that contain certain vitamins and minerals that can help the body make melatonin. And there are a few foods that actually contain melatonin – however the supposition that eating melatonin-containing foods will help you sleep is likely unfounded since measurements of plasma melatonin after consuming such foods showed that the increase in melatonin was not consistent with the amount of melatonin ingested. Interestingly, there was increased excretion of melatonin metabolite after consuming melatonin rich foods. The authors of a particular review stated “it is concluded that studies reporting the appearance of melatonin in blood and its metabolites in urine following ingestion of melatonin-rich foods are flawed”.

But the following four vitamins and minerals found naturally in food can help your body produce melatonin, and therefore promote better sleep:

  • Tryptophan – this is an amino acid which is turned into serotonin, a neurotransmitter, after which it is then converted into melatonin. Foods that contain tryptophan are red meat, poultry, fish, eggs, dairy products, seafood, nuts and seeds, avocados, seaweed, spinach, broccoli, asparagus.
  • Magnesium – this is a natural muscle relaxant and is commonly used in baths as Epsom salts or magnesium flakes to help relax sore muscles after a workout. It helps to deactivate adrenaline and is useful in and of itself as a natural sleep aid. Foods that contain magnesium are nuts, shellfish, sardines, salmon, liver, steak, heart, dark leafy greens, seaweed.
  • Calcium – this mineral helps in the production of melatonin in the brain. A diet rich in calcium has been shown to help those suffering with insomnia. Natural food sources include milk, cheese, yogurt, sardines, pilchards, bone broth, broccoli, cabbage, seeds.
  • Vitamin B6 – this is required to help convert tryptophan into melatonin, so even if you are taking in enough tryptophan it is important to also make sure your B6 intake is also adequate. Foods that contain this important vitamin are beef liver, organ meats, tuna, salmon, chicken, nuts, spinach, chickpeas.

To Supplement Or Not?

The use of exogenous melatonin has recently been studied, as it appears that it can influence the body’s own secretion of melatonin. This is being used as a treatment for disorders of circadian rhythms such as rapid time-zone change syndrome, insomnia, delayed sleep phase syndrome and de-synchronisation of biological rhythms in the blind or shift workers. Exogenous melatonin was first introduced as a treatment for sleep disorders twenty-one years ago, and was developed by neuroscientist Dr Richard Wurtman. In Canada and the USA it is freely available over the counter, but in the UK it is a prescription only medication. It is not FDA approved, and in Australia and Europe it is approved only for those over the age of 54 with sleeping issues. Many of the products that are available contain dosages that are much higher than the body naturally produces – and a typical dose may elevate blood levels from between 1-20 times higher than normal! Studies show that melatonin supplementation is only appropriate for certain types of sleep problems such as shift work issues, jet lag/rapid time-zone changes, blind persons and children with developmental disorders, and it only works if taken at the appropriate time of day, otherwise it may actually reset the circadian rhythm to the wrong time of day. Whilst there is currently no evidence that exogenous melatonin is addictive it can still cause side effects such as:

  • Nausea
  • Headaches
  • Dizziness
  • Irritability
  • Mild tremors
  • Low blood pressure
  • Stomach cramps
  • Short term depression

If taken as a long-term medication melatonin has been shown to disrupt natural hormone levels and even sabotage sleep. Because melatonin naturally lowers core body temperature, excess levels in the blood can cause hypothermia to occur and stimulate over production of prolactin (the hormone that women produce when breastfeeding), which can result in hormonal problems and even liver and kidney issues in men. Dr Wurtman himself stated “With some hormones, if you take too much you can really put your body in danger. With melatonin, you’re not in danger, but you’re also not very comfortable. It won’t kill you, but it’ll make your life pretty miserable”. Taken over an extended period of time can result in the body producing less of its own, making the situation worse, and ultimately a vicious cycle.

So, the bottom line is to do everything you can to help your body to produce melatonin naturally. Sleep hygiene techniques, as discussed above, along with eating foods that can help your brain make melatonin, and implementing relaxation strategies as mentioned in the cortisol section, should be all that you need to get a good night’s sleep.


And on that note, I wish you all sweet dreams as I am off to relax for a couple of hours before bed!