Circadian Rhythms and Sleep

Sleep and Circadian Rhythm disruption are very common in ME/CFS, Long Covid and Fibromyalgia.  Circadian rhythms — the body's internal 24-hour clock — play a vital role in regulating sleep, metabolism, hormone release, and digestion. When disrupted, they can significantly affect health, particularly people with ME/CFS, Long Covid and Fibromyalgia, where sleep disturbances and fatigue are common.

Disrupted circadian rhythms impair not only sleep but also affect mood, immunity, cognition, and physical recovery. This blog explores how circadian rhythms influence physical and mental wellbeing, the specific ways they are disrupted in ME/CFS, Long Covid, and Fibromyalgia, and how consistent sleep and eating patterns can help improve well-being and symptoms.

1. WHAT ARE CIRCADIAN RHYTHMS?

Circadian rhythms are 24-hour cycles in the physiological processes of living beings, governed by the body’s internal clock and strongly influenced by environmental light. In humans, these rhythms regulate sleep-wake cycles, hormone release, digestion, metabolism, and even immune function.

At the centre of this system is the suprachiasmatic nucleus (SCN) in the hypothalamus — our "master clock". The SCN responds primarily to light and orchestrates daily fluctuations in hormones like cortisol (which promotes wakefulness) and melatonin (which promotes sleep).

Disruptions to circadian rhythms have been linked to:

• Insomnia and other sleep disorders

• Metabolic syndrome and obesity

• Depression and mood disorders

• Immune dysregulation

• Neurodegenerative diseases

Factors such as shift work, jet lag, irregular bedtimes, artificial blue light exposure, and certain medical conditions (including ME/CFS, Long Covid and Fibromyalgia) can disturb these rhythms and lead to widespread health impacts.

Some of the factors which can disrupt circadian rhythms are shown below:

2. CIRCADIAN RHYTHM & SLEEP DISRUPTION IN ME/CFS, LONG COVID AND FIBROMYALGIA

Circadian rhythm disruption in ME/CFS

Sleep disturbance is a hallmark symptom of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), often described as "unrefreshing sleep".

Research shows that:

• 91.9% of people with ME/CFS report sleep issues (De Becker et al., 2001)

• 96.8% report non-restorative sleep (Davidson et al., 2017)

• These sleep issues often persist over time and vary in presentation

Circadian rhythm disruption in Long Covid

In Long Covid, up to 40% of individuals report poor sleep quality, insomnia, fragmented sleep, or hypersomnia. Both conditions are believed to involve disrupted circadian regulation — not only in the brain (central clock) but also in peripheral organs.

Emerging evidence (McCarthy, 2022) suggests:

• Inflammation  increase levels of TGFB peptides which may disrupt the alignment of circadian rhythms

• Other factors, such as insufficient oxygen and poor light exposure may worsen this alignment and weaken central rhythms

• This misalignment can explain symptoms common in both ME/CFS and Long Covid: fatigue, brain fog, autonomic instability, cold intolerance, and mood disturbances.

Diagram showing how inflammation may increase TGFB peptides and disturb circadian rhythms leading to symptoms of ME/CFS and Long Covid (McCarthy, 2022)

Circadian rhythm disruption in Fibromyalgia (FM)

Sleep is often disturbed in FM and research suggests disrupted circadian regulation of hormones and body functions in FM, including:

• Cortisol dysregulation - blunted diurnal variation, with lower morning cortisol and elevated evening levels are found in FM, and these characteristics are associated with fatigue and pain

• Melatonin deficiency - some studies report reduced nocturnal melatonin secretion in FM, which may contribute to insomnia, increased pain perception, and altered thermoregulation

• Core body temperature rhythm - altered thermoregulation may contribute to circadian rhythm disruption in FM

3.   SUPPORTING CIRCADIAN RHYTHMS TO IMPROVE SLEEP

What do we mean by healthy sleep?

Healthy sleep is timed, restorative, and rhythmic. It should follow a predictable pattern across the night, cycling through:

• Non-REM stages (light to deep sleep)

• REM sleep (important for memory and emotional processing)

Key features of healthy sleep:

• Duration -  7+ hours/night

• Quality - adequate time in deep and REM sleep

• Consistency - same sleep/wake times every day

• Alignment - sleep matches natural light-dark cycles

Hormones and sleep

There are two hormones that have a particular impact on our sleep-wake cycle, and these are Cortisol and melatonin. These two hormones follow opposite rhythms:

• Cortisol peaks in the morning to promote alertness

• Melatonin peaks at night to support sleep

Blue light and hormones

Blue light is a type of light that comes from the sun, and being outside exposes you to it. Blue light also comes from digital screens and LED lights in the home.

Blue light in the morning - blue light in the morning is very helpful to our circadian rhythms Getting outside first thing in the day and getting exposure to blue light at that time of day increases our alertness during the day. It also helps to stimulate the production of melatonin in the evening, helping us to sleep better at night

Blue light in the evening - however, exposure to blue light in the evening can delay the onset of sleep as it reduces the production of melatonin. Switching off screens or using blue light filters in the evening will help support the release of melatonin in the evening, as shown below:

Routine to support your circadian rhythms and sleep patterns

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. This may be difficult for some people with M.E/CFS who may have fluctuating energy levels – but it is worth trying

• Try to keep to a regular bed-time 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

Winding down before bed

• Reduce blue light 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 e.g reading, listening to music, relaxation exercises

• Meditation can be very helpful – e.g mindfulness, can help with relaxation and reducing stress  Guided meditations can be found on-line

Some people find a warm bath before bed is relaxing - it can bring the body temperature to the right level for falling asleep. However, not everyone with M.E. can tolerate warm baths.

How to make your bedroom sleep-friendly

You can also take action to make sure that your bedroom provides a suitable environment in which to sleep, as shown below. We generally sleep better in a slightly cooler room, and one which is quiet and without light. Some suggestions on how to make your bedroom suited to good sleep are shown below:

4.  PRACTICAL TIPS FOR EATING IN LINE WITH YOUR BODY CLOCK

Our digestive system also follows a circadian rhythm, coordinated by the SCN and peripheral “clocks” in the gut, liver, pancreas, and microbiome.

Ways to align eating habits with your biological clock

a) Avoid Irregular or late-night eating as this can:

• Disrupt hormone rhythms (e.g. insulin, ghrelin, cortisol) and reduce melatonin

• Interfere with gut repair and digestion

• Contribute to reflux, constipation, or inflammatory responses

• Alter the gut microbiota, which itself influences circadian regulation and sleep quality

b) Eat your meals at the same time each day and avoid random eating patterns - consistent mealtimes help support biological clocks. When food arrives regularly at the same time, all the clock processes in the digestive system work together for efficient digestion and elimination.

c) Breakfast and dinner are the most important meals to align with with your circadian rhythm as they signal the start and the end of your eating

d) Consider Time-Restricted Eating (TRE) — eating within a 10–12-hour daytime window — supports autophagy, reduces inflammation, and enhances metabolic health

e) Avoid grazing all day  as htis prevents digestive rest, and may lead to risk of a “leaky gut” and microbiome imbalance

f) Avoid eating within 3-4 hours of bed-time

REFERENCES

Davidson, Sean L.; Gotts, Zoe M.; Ellis, Jason G.; Newton, Julia L. (March 2017), "Two year follow-up of sleep diaries and polysomnography in chronic fatigue syndrome: a cohort study", Fatigue: Biomedicine, Health & Behaviour, https://doi.org/10.1080%2F21641846.2017.1297280

 "Proposed Diagnostic Criteria for ME/CFS". nationalacademies.org. 2015

 De Becker, Pascale, et al 2001A definition‐based analysis of symptoms in a large cohort of patients with chronic fatigue syndrome". Journal of Internal Medicine. 250 (3): 234–240. doi:10.1046/j.1365-2796.2001.00890.x.

Maksoud R, et al. Systematic Review of Sleep Characteristics in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Healthcare (Basel). 2021 May 11;9(5):568. doi: 10.3390/healthcare9050568. PMID: 34065013; PMCID: PMC8150292. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8150292/

Mohamed AZ, et al. Objective sleep measures in chronic fatigue syndrome patients: A systematic review and meta-analysis. Sleep Med Rev. 2023 Jun;69:101771. doi: 10.1016/j.smrv.2023.101771. Epub 2023 Mar 9. PMID: 36948138; PMCID: PMC10281648.

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

Froy, Oren. (2012). Circadian Rhythms and Obesity in Mammals. ISRN obesity. 2012. 437198. 10.5402/2012/437198.

McCarthy MJ. Circadian rhythm disruption in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Implications for the post-acute sequelae of COVID-19. Brain Behav Immun Health. 2022 Jan 10;20:100412. doi: 10.1016/j.bbih.2022.100412. PMID: 35465246; PMCID: PMC9019698. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9019698/