Sunlight, Red Light Therapy and ME/CFS, Long COVID & Fibromyalgia: Could Light Support Recovery?

For most of human history, we spent a great deal of time outdoors and were exposed to the full spectrum of natural daylight. Today, many of us spend most of our lives indoors, and this can be particularly true for people with ME/CFS, Long COVID or fibromyalgia, who may be limited by fatigue, pain, post-exertional malaise (PEM), dizziness or light sensitivity.

So could light itself have a role in supporting health?

There is increasing scientific interest in the biological effects of sunlight beyond vitamin D, as well as in photobiomodulation (PBM), the use of specific wavelengths of red and near-infrared light therapeutically. The evidence is still developing, particularly for ME/CFS and Long COVID, but there are some fascinating potential mechanisms involving circulation, mitochondria, inflammation and the nervous system.

Importantly, light therapy should currently be regarded as a potential supportive strategy rather than a proven treatment or cure.

Sunlight does much more than make vitamin D

For many years, the main health benefit attributed to sunlight was its ability to stimulate vitamin D production in the skin. Vitamin D is undoubtedly important, particularly for calcium metabolism and bone health, and severe deficiency can cause rickets or osteomalacia.

However, the relationship between sunlight and health appears to be considerably more complicated.

A 2024 review by dermatologist and researcher Richard Weller highlighted evidence that sunlight may influence health through pathways that are independent of vitamin D.

Epidemiological studies from the UK and Sweden have associated greater sunlight exposure with lower all-cause and cardiovascular mortality, although these studies cannot prove that sunlight itself caused the reduction in risk. (PubMed)

This is particularly interesting because large randomised trials of vitamin D supplementation have generally failed to reproduce many of the health benefits associated observationally with higher vitamin D levels. This suggests that vitamin D may sometimes be a marker of healthy sunlight exposure rather than the explanation for all of its effects.

Sunlight, nitric oxide and circulation

One of the most interesting mechanisms involves nitric oxide (NO).

Nitric oxide is a signalling molecule that helps blood vessels relax and widen. This can improve blood flow and reduce blood pressure. The skin contains stores of nitrogen-containing compounds, and research from Weller's group and others has shown that UVA exposure can mobilise nitric oxide from the skin into the circulation. This can produce vasodilation and lower blood pressure independently of vitamin D production.

Why might this matter in ME/CFS and Long COVID?

Research into both conditions has identified abnormalities involving blood vessels, endothelial function, autonomic regulation and circulation in at least some patients. Reduced cerebral blood flow and orthostatic intolerance are also areas of considerable interest.

It is therefore biologically plausible that improved vascular function could be helpful for some symptoms. However, this is not the same as demonstrating that sunlight treats ME/CFS, Long COVID or POTS. Clinical trials specifically testing sunlight exposure in these conditions are still lacking.

Sunlight and your body clock

There is another much more established reason to get outside: light is one of the most powerful regulators of the circadian rhythm.

Morning daylight reaches specialised light-sensitive cells in the retina, which communicate with the brain's central body clock. This helps regulate the timing of melatonin, cortisol, sleepiness and alertness.

People with ME/CFS and Long COVID commonly report disrupted or unrefreshing sleep, while some develop delayed sleep patterns. Regular exposure to outdoor light, particularly in the morning, can therefore be a simple way of strengthening the body's day-night signal.

This doesn't require sitting in intense sunshine. Daylight itself is the important stimulus, so a gentle morning sit in the garden, on a balcony or outside the front door may be worthwhile even when direct sunshine isn't available.

What about inflammation and immunity?

Sunlight also appears to influence the immune system. Research has identified seasonal changes in immune-related gene expression, inflammatory signalling and other physiological processes. UV exposure can alter molecules in the skin such as urocanic acid and can influence immune pathways.

This is potentially relevant because altered immune and inflammatory signalling has been reported in subsets of people with Long COVID and ME/CFS.

However, this is an area where it is particularly important not to overstate the evidence. We do not currently know that increasing sunlight exposure will reduce the chronic inflammation associated with either illness. These are interesting biological mechanisms that require much more clinical research.

Enter red and near-infrared light

Photobiomodulation (PBM), often called red light therapy or near-infrared light therapy, is different from simply sitting in the sun.

PBM uses LEDs or lasers to deliver specific wavelengths of light, commonly in the red and near-infrared regions. Unlike sunlight, therapeutic PBM devices do not need to expose the skin to UV radiation.

Red light is generally in the region of approximately 630–670 nm, while near-infrared devices commonly use wavelengths around 810–850 nm.

These wavelengths can penetrate tissues to different depths and interact with cellular processes. One of the main proposed targets is the mitochondria.

Could red light support the mitochondria?

Mitochondria are often described as the cell's energy-producing structures. They convert nutrients into ATP, the energy currency used by cells.

Photobiomodulation appears to interact with mitochondrial signalling, including pathways involving cytochrome c oxidase, nitric oxide, reactive oxygen species and cellular signalling.

Experimental research suggests PBM can influence ATP production, oxidative stress, inflammation and mitochondrial function.

This is particularly interesting in ME/CFS because abnormalities in energy metabolism and mitochondrial function have been extensively investigated in the condition. But there is an important distinction:

A biological mechanism is not proof of a clinical treatment.

We cannot currently say that red light therapy corrects the underlying energy abnormalities of ME/CFS or Long COVID. More clinical research is needed.

What does the research show for Long COVID?

The evidence is beginning to move beyond theory.

A recent randomised, double-blind, sham-controlled pilot trial investigated home-based transcranial and intranasal photobiomodulation for cognitive dysfunction ("brain fog") in people with post-COVID-19 condition. This is particularly interesting because cognitive dysfunction is one of the most disabling symptoms reported by many people with Long COVID. (PubMed)

There have also been smaller studies investigating PBM for specific Long COVID symptoms, including taste dysfunction. (PubMed)

These early findings are encouraging, but they are not yet sufficient to establish PBM as an effective treatment for Long COVID overall.

What about fibromyalgia?

Here the evidence is somewhat more developed.

A 2025 umbrella review covering 204 randomised controlled trials of PBM across multiple conditions found moderate-certainty evidence for improvement in several outcomes, including fatigue in fibromyalgia, although the quality and consistency of evidence varied substantially between conditions. (PubMed)

Even more recently, a 2026 systematic review identified seven randomised controlled trials of PBM in fibromyalgia. Overall, the studies suggested short-term improvements in pain and quality of life, with some evidence for sleep and psychological outcomes. However, the researchers emphasised substantial differences between treatment protocols and called for larger, better-standardised trials. (PubMed)

So fibromyalgia currently has a more substantial clinical evidence base for PBM than ME/CFS.

That doesn't mean that everyone with fibromyalgia will benefit – but it does make PBM a particularly interesting area for further research.

How could you try sunlight safely?

For someone with ME/CFS or Long COVID, the key principle is little and often.

You don't need to go for a long walk to benefit from being outdoors.

Try:

• Spending 10–20 minutes outdoors in the morning, if tolerated.

• Sitting in a garden, on a balcony or outside your front door.

• Getting daylight soon after waking.

• Increasing exposure gradually rather than having occasional prolonged exposure.

• Choosing cooler times of day if heat worsens your symptoms.

• Staying hydrated, particularly if you have orthostatic intolerance or POTS.

• Avoiding sunburn and excessive UV exposure.

  
  

Most importantly, don't turn sunlight exposure into an exercise programme. Sitting quietly outside can be just as useful for obtaining daylight as walking around the garden.

For people with severe ME/CFS, even a few minutes may be enough to start with.

What about red light therapy?

If you are considering a PBM device, remember that more is not necessarily better. PBM appears to have a dose-response relationship in which insufficient light may have little effect, while excessive exposure may reduce the benefit. Treatment protocols used in research vary considerably in wavelength, power, dose, treatment time and treatment location.

For someone with ME/CFS or Long COVID, a cautious approach would therefore be sensible.

For example, you might start with a short exposure for just a few minutes, a couple of times per week, rather than immediately following the treatment schedule used in a commercial product.

Monitor:

• fatigue

• sleep

• headaches

• dizziness

• pain

• cognitive symptoms

• and, crucially, whether symptoms deteriorate over the following 24–72 hours.

  
  

If treatment appears to trigger PEM, reduce the dose or stop.

Can nutrition enhance the effects?

There is an interesting nutritional connection with one of sunlight's mechanisms: nitric oxide.

Dietary nitrate can be converted through the nitrate → nitrite → nitric oxide pathway. Good food sources include:

• beetroot

• rocket

• spinach

• lettuce

• celery

• watercress.

  
  

Studies of beetroot juice and dietary nitrate have found reductions in blood pressure in some populations, although the size and consistency of the effect varies between studies. (PubMed)

It is tempting to suggest that combining nitrate-rich foods with sunlight would produce a synergistic effect, but this has not been demonstrated in ME/CFS or Long COVID, so it should be regarded as a hypothesis rather than a proven treatment combination.

Other nutrients are relevant to mitochondrial function, including magnesium, riboflavin (vitamin B2), CoQ10 and adequate protein. CoQ10 is a component of the mitochondrial electron transport chain, and a meta-analysis of 13 randomised trials found a modest reduction in fatigue with CoQ10 supplementation across mixed populations. However, a 2025 systematic review of supplements specifically in ME/CFS concluded that evidence remains too heterogeneous and methodologically limited to draw firm conclusions. (PubMed)

So rather than looking for a "light therapy supplement", the sensible approach is to ensure that the diet provides the nutrients required for normal mitochondrial and vascular function.

Don't forget the most important treatment: pacing

For people with ME/CFS, there is one particularly important caveat.

Light therapy should never be used as a reason to push through symptoms.

If sitting outside for 20 minutes is fine but walking for 20 minutes causes PEM, sit outside. If five minutes of red light feels fine but ten minutes causes a delayed flare, five minutes may be your current limit – or the treatment may simply not suit you.

The objective is not to "train" the body by progressively increasing exposure regardless of symptoms. It is to find an amount that your individual system tolerates.

The bottom line

Sunlight and red/near-infrared light are fascinating areas of research for ME/CFS, Long COVID and fibromyalgia. Sunlight influences much more than vitamin D, with potential effects on nitric oxide, circulation, circadian rhythms and immune signalling. Photobiomodulation may influence mitochondrial and cellular signalling and has produced promising results in conditions including fibromyalgia, while early research in Long COVID is beginning to investigate brain fog and other symptoms.

But there is still a large gap between promising biology and proven clinical treatment.

For now, sensible exposure to natural daylight is a relatively simple lifestyle strategy, provided it is adapted to your symptoms, skin type, climate and tolerance. Red and near-infrared light therapy is more experimental and should be approached cautiously, particularly by people who experience PEM.

The most useful way to think about light is perhaps not as a miracle treatment, but as another environmental signal that interacts with our biology. Combined with appropriate pacing, nourishing food, good sleep and management of individual symptoms and comorbidities, it may eventually prove to be an important part of the picture.

Key references

• Weller RB. Sunlight: Time for a Rethink? Journal of Investigative Dermatology. 2024;144:1724–1732. doi:10.1016/j.jid.2023.12.027. (PubMed)

• Effects of photobiomodulation on multiple health outcomes: an umbrella review of randomized clinical trials. 2025. (PubMed)

• Swathi G, et al. Effect of photobiomodulation on pain and quality of life in fibromyalgia syndrome: a systematic review. Lasers in Medical Science. 2026;41:125. (PubMed)

• Navarro-Ledesma S, et al. Short-Term Effects of Whole-Body Photobiomodulation on Pain, Quality of Life and Psychological Factors in a Population Suffering from Fibromyalgia. Pain and Therapy. 2023;12:225–239. (PubMed)

• Photobiomodulation for cognitive dysfunction (Brain Fog) in post-COVID-19 condition: a randomized double-blind sham-controlled pilot trial. eClinicalMedicine. 2026. (PubMed)

• Bonilla Ocampo DA, et al. Dietary Nitrate from Beetroot Juice for Hypertension: A Systematic Review. Biomolecules. 2018;8:134. (PubMed)

• Tsai I-C, et al. Effectiveness of Coenzyme Q10 Supplementation for Reducing Fatigue: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Frontiers in Pharmacology. 2022. (PubMed)

• Dietary Supplementation for Fatigue Symptoms in ME/CFS—A Systematic Review. 2025. (PubMed)