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  • Writer's pictureIsabel Hemmings

Do you need a regular bedtime?

Why should the time we go to sleep at night make a difference to our health? In what way could the timing and regularity of our meals effect our wellbeing? In recent years the science of circadian rhythms has shown us how the regularity and pattern of our daily lives affects how we feel and can even impact our risk of disease.  Here we outline the workings of our 24-hour body clock and provide our ten top tips on how to align your daily patterns with your internal body clock.



What are Circadian Rhythms?

 

A circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours:

 

  • Circadian rhythms regulate cycles of alertness and sleepiness by responding to light changes in our environment

  • These rhythms are driven by the body's internal biological clock, which is synchronised with external cues such as light and darkness

  • Circadian rhythms are found in most living organisms, including animals, plants, and even some bacteria

 

The SCN – the central pacemaker

 

The SCN, or the suprachiasmatic nucleus, is the body’s innate timing device. It is a small region located in the hypothalamus of the brain. It serves as the master pacemaker for circadian rhythms in all mammals, including humans. The SCN consists of around 20,000 neurons and is critical for coordinating the timing of various physiological processes and behaviours with the external light-dark cycle.

 

The SCN synchronises the body's internal circadian rhythms with the external light-dark cycle. The SCN responds to the outside world - light-sensitive cells in the retina of the eyes send signals to the SCN, so that the body knows it is daytime. The cells in the retina are particularly sensitive to blue light, which is found in natural light, particularly in sunshine during the day.

 

Light exposure during the day helps reset the SCN's internal clock, so that physiological processes are appropriately timed within the day-night cycle, e.g

 

  • the sleep-wake cycle

  • hormone secretion

  • body temperature regulation

We are grateful to the Oklahoma Otolaryngology Associates for the use of this image



The sleep-wake cycle

 

The SCN plays a crucial role in regulating the timing of the sleep-wake cycle and the hormones which govern our sleep-wake cycle. Many hormones fluctuate throughout the 24-hr circadian cycle - cortisol and melatonin are two hormones which are essential in the sleep-wake cycle, and overall in circadian balance.

 

The SCN promotes wakefulness during the day and signals the release of the hormone melatonin from the pineal gland during the evening and night, which helps facilitate sleep.

 

Cortisol – wakes us up

Cortisol is a stress hormone, and under healthy circumstances, cortisol levels peak in the morning, decline throughout the day, are lowest in the evening, and slowly rise overnight. A disruption in cortisol rhythm can lead to restless sleep, inadequate stress response, and increased pro-inflammatory proteins. 

 

Melatonin – promotes sleep

Melatonin and cortisol have an inverse relationship. Under normal circumstances, melatonin is lowest in the morning, increases throughout the day, is highest in the evening, and slowly declines overnight.Melatonin production is significantly impacted by light exposure

  • As the sun sets, the SCN signals to the pineal gland to produce more melatonin, promoting rest and sleep

  • When the sun comes up, the SCN signals to the pineal gland to slow down melatonin production, preparing the body for the day ahead


Beyond sleep, melatonin is an important antioxidant that has anti-inflammatory and neuroprotective benefits.

 

Blue light and our circadian rhythms


Blue light is found in natural light outdoors, particularly sunshine, and it affects the SCN and the hormones which govern our sleep-wake cycle. Ever since humans have been on the Earth, blue light from daylight has governed our sleep-wake cycle. Exposure to blue light in the morning helps to increase our alertness during the day, but it also helps to stimulate the release of melatonin 14-16 hours later, which helps us to sleep overnight.


But in our lives today, we also have artificial light as well as natural light, which helps us to live our lives during darker hours. Too much blue light from LED lights and digital equipment such as lap-tops and phone in the evenings can interfere with our circadian rhythms, causing disruption to sleep.




The SCN and peripheral clocks, and digestion

 

The body also has peripheral circadian clocks including clocks in the liver, pancreas, gut, fat cells and muscles.The SCN affects peripheral clocks in organs in the body so that these clocks also synchronise with the external environment.

 

For example, the clock in the gut determines:

  • when to produce gut hormones for hunger or satiety,

  • produce digestive juices,

  • absorb nutrients

  • move waste from the colon

 

The clock in the pancreas determines when to produce insulin and when to slow down. Other cues such as food, exercise, oxygen levels and pH also affect circadian rhythms in peripheral tissues.

 

 Regular food patterns are important for good health:

 

  • When food arrives regularly at the same time, all the clock processes in the digestive system work together for efficient digestion and elimination.

  • When food arrives at a time of day when the gut is not anticipating it, e.g the middle of the night food is not digested properly and the normal repair processes in the gut may be upset. This can damage to the gut, and over time cause disease.

  • If we eat three meals every day – e.g 8am, 1pm and 6pm our digestive systems learns to anticipate these meals and to release digestive enzymes and acids as needed to help digestion

  • Random eating patterns can cause problems e.g Acid reflux, heartburn, GORD, Indigestion, IBS, irregular bowel movements or constipation

  • Random eating patterns can change the composition of gut bacteria, which can lead to leaky gut – which may lead to inflammation and impact on the immune system

  • Research has shown a connection between disrupted circadian rhythm and melatonin production, and the onset of gastrointestinal diseases like GORD, peptic ulcer disease, and IBS (Konturek 2011)

 


What can disrupt our Circadian Rhythms?

 

There are many factors which can lead to circadian misalignment as shown below:



 

Types of Circadian Rhythm disorder

There are a number of different circadian rhythm disorders:



What happens when our body clock is out of alignment with circadian rhythms?

 

Disruption of the circadian rhythm increases risk for many health conditions including:

  • Sleep disorders like insomnia or sleep deprivation, which can negatively impact physical and mental health

  • Increased risk of metabolic health problems such as obesity, pre-diabetes and type 2 diabetes

  • Increased susceptibility to infections and inflammatory conditions

  • Increased risk of cardiovascular diseases, including hypertension, coronary artery disease and  stroke

  • Impaired cognitive function and increased risk of accidents and errors

  • Increased risk of mood disorders e.g depression and bipolar disorder

  • Increased risk of certain types of cancer, e.g breast cancer and colorectal cancer

 

Whilst metabolic conditions, such as cardiovascular disease, obesity and type 2 diabetes may take years to develop, research on people who work shifts, shows that over time, disrupted circadian rhythms increase risk for type 2 diabetes and obesity by 10-40% (Daniels, 2023).

 

Circadian misalignment such as disrupted sleep may increase cortisol secretion in the late afternoon and early evening, which may interfere with sleep later – a vicious circle. Higher cortisol in the afternoon has also been shown to induce insulin resistance. (O’Byrne, 2021)

 

Ten top tips to get in sync with your circadian rhythms

 

A)   SLEEP PATTERNS AND ROUTINE

 

If you have difficulty sleeping or have disrupted sleep patterns here are some steps you can do to try and bring your sleeping patterns into alignment with your circadian rhythms.

 

1. Maximise blue light first thing in the morning

 

Blue light in the morning is extremely helpful for our circadian rhythms.

Blue light is a type of light that comes from the sun, and being outside in natural light exposes you to blue light. This exposure to blue light increases alertness during the day, but also helps the body to produce melatonin in the evening 14-6 hours later.


2. Minimise blue light in the evening 


Blue light exposure in the evening is detrimental to our circadian rhythms and can lead to disrupted sleep. Blue light can be emitted from digital screens and LED lights

 

Blue light in the evening reduces the release of melatonin. Blue light can be reduced by:

•       Set phones and screens to night shift from 7pm to 7am

•       Switch lighting to lower level, softer lighting, and dim overhead lights

•       Avoid screens for 2 hours before bed.

 

3. Adopt routine sleeping habits

 

Routine is key – it helps us to establish strong circadian rhythms. If possible, try to have a regular time for going to bed every night and for getting up each morning. Try to keep to a regular bedtime and getting up time even at weekends. If your body clock has moved forward – i.e you go to sleep later and wake later,  try to gradually bring sleep forward by a few minutes each day

 

4.    Eat protein rich foods for tryptophan


Tryptophan is an amino acid which is found in protein-rich foods. It is used in the body to make the serotonin and melatonin. A diet low in tryptophan impairs sleep and several studies have shown that eating tryptophan-enriched foods improves sleep. In one study of older adults an increase in total sleep time, sleep efficiency, and immobile time was noted after regular intake of tryptophan. Another study found that a combination of bright light in the morning and a tryptophan rich diet increased melatonin production in the evening substantially more than a low tryptophan diet with dim light in the morning

 

5.    Wind down in the evenings


Try and prepare for bed by winding down in the evenings – do things that you find relaxing in the hours before bed such as reading, listening to music or relaxation exercises. Some people find meditation, such as mindfulness meditation, very helpful for reducing stress and increasing relaxation in the evenings before bed. (Guided meditations can be found online). A warm bath before bed can be very relaxing – and it can bring the body temperature to the right level for falling asleep.

 

6.    Make sure your bedroom is right for sleep


Make sure you have a comfortable environment in which to sleep at night, paying particular attention to  noise, temperature and darkness as shown below:

 



B)   REGULARISE EATING PATTERNS

 

7.    Adopt regular eating patterns

Eat breakfast, lunch and dinner at approximately the same time each day. Adopting a regular eating pattern supports a good circadian rhythm which helps with sleep. Breakfast and dinner are the most important meals to align with your circadian rhythm as they signal the start and the end of your eating day.

 

8.    Avoid grazing throughout the day


Eating snacks during the day leaves no downtime between meals. The stomach and intestinal lining are unable to repair themselves properly between meals, potentially leading to ulcers or leaky gut. Blood sugars can go on a roller-coaster ride if we constantly snack.

 

9.    Avoid eating late in the evening or at night


Food eaten in the evening stimulates five times more acid production than food eaten in the morning. Saliva production decreases at night by 9/10ths –  this helps us to sleep. Daytime saliva neutralises stomach acid that may reflux into oesophagus but there is insufficient saliva to neutralise night-time acid. Late night eating is therefore more likely to trigger acid reflux/heartburn, which, over time, can damage the oesophageal lining. Since the intestinal phase of digestion slows down over night, food eaten late in the evening may stay in the stomach bathed in acid to prevent bacterial growth, with increased risk of constipation.

 

10.    Consider Time Restricted Eating (TRE)


There is good evidence that TRE helps to regularise the digestive clock and helps to align your eating schedule with your circadian rhythm.  TRE is a dietary approach that restricts the time window during which food is eaten during the day. The most common form of time-restricted eating involves fasting for a certain number of hours overnight, such as fasting for 12 - 16 hours and consuming all meals within an 8 - 12hour window. Start by eating within a 12- hour eating window, with no food or drinks outside these hours – other than water, herb tea, black tea or cofffee. Then gradually reduce your eating window down to 10 or 11 hours.

 


Summary - how to get back in sync with your circadian rhythms 

 

In summary, here are our top tips for getting back in sync with your internal body clock:




References

 

Daniels LJ, Kay D, Marjot T, Hodson L, Ray DW. Circadian regulaƟon of liver metabolism: experimental approaches in human, rodent, and cellular models. Am J Physiol Cell Physiol. 2023 Nov 1;325(5):C1158-C1177. doi: 10.1152/ajpcell.00551.2022. Epub 2023 Aug 29. PMID: 37642240.

 

Dos Santos A, Galiè S. The Microbiota-Gut-Brain Axis in Metabolic Syndrome and Sleep Disorders: A Systematic Review. Nutrients. 2024 Jan 29;16(3):390. doi: 10.3390/nu16030390. PMID: 38337675; PMCID: PMC10857497. https://pubmed.ncbi.nlm.nih.gov/38337675/#:~:text=Results%3A%20This%20systematic%20review%20highlights,on%20MetS%20or%20sleep%20disturbances.

 

Fukushige, H., Fukuda, Y., Tanaka, M. et al. Effects of tryptophan-rich breakfast and light exposure during the daytime on melatonin secretion at night. J Physiol Anthropol 33, 33 (2014). https://doi.org/10.1186/1880-6805-33-33

 

Diana E. Gutierrez Lopez, et al . Circadian rhythms and the gut microbiome synchronize the host’s metabolic response to diet, Cell Metabolism, Vol 33, Issue 5, 2021, https://doi.org/10.1016/j.cmet.2021.03.015.

 

Konturek PC, et al Gut clock: implication of circadian rhythms in the gastrointestinal tract. J Physiol Pharmacol. 2011 Apr;62(2):139-50. PMID: 21673361

 

O'Byrne NA, et al (2021) Sleep and Circadian Regulation of Cortisol: A Short Review. Curr Opin Endocr Metab Res. 2021 Jun;18:178-186. doi: 10.1016/j.coemr.2021.03.011. Epub 2021 May 5. PMID: 35128146; PMCID: PMC8813037.

 

Panda,S  2018 The Circadian Code. Vermilion, London. https://bit.ly/3VR1u33

 

Tahara, Y., et al, (2018). Gut Microbiota-Derived Short Chain Fatty Acids Induce Circadian Clock Entrainment in Mouse Peripheral Tissue. Scientific reports, 8(1), 1395. hƩps://doi.org/10.1038/s41598-018- 19836-7

 

 


 

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