Light is good for the microbes on our skin and in our gut

Paper reviewHuman microbiomeMicrobiotaSunlight
Written By Michael Butler

"Photobiomics": Can Light, Including Photobiomodulation, Alter the Microbiome? (2019)

 

In a nutshell

  • UV and IR light are both good for the beneficial microbes on our skin and in our gut

  • The way this works is still not understood

  • Mounting evidence points to the benefits of sunlight for human health

 
 

Context

This summer (2024) I’ve actively tried to get as much safe exposure to sunlight as possible. I’ve felt the positive effects of this, done some research into the subject of the human health effects of natural sunlight, and recently described what I’ve found. Shortly after publishing that article, I ran across this review paper which addresses, at least to some extent, the deficit of information I’d been able to find about the effects of light on the human microbiome.


Objective and results of the investigation

The review contains the following sections:

  • Introduction to Light Therapy and the Microbiome

  • Photobiomodulation (PBM)

  • Human Microbiome

  • Microbiome and Human Disease

  • PBM Alters the Microbiome

  • Mechanisms of Action of PBM on the Microbiome

  • Potential Application to Human Disease

  • Conclusions

The authors clearly are not well versed in the nature of the human microbiome, human diet and human diseases, and I describe my reservations below. Nevertheless, I believe this review is still useful for someone, like me, who is new to the field of PBM.


The review of the literature found the following effects:

  • Treatment of mice by shining light on their bellies

    • Affected the types of bacteria present in a way described as healthy

    • Near infrared (NIR) light was more effective than visible red light

  • Preliminary treatment of humans showed apparently beneficial changes to gut bacteria

  • Healthy effect of UV on blood

  • Unhealthy effects of UV on skin microbiome

To their great credit, the authors describe any discussion of possible mechanisms of action as “highly speculative”, and state:

 
“The key question that must be addressed by further research is whether the light is primarily absorbed by the microbial cells themselves that make up the human microbiome, by the host cells that surround the microbes (or indeed cells that are distant from them), or by a combination of both microbes and host cells”
 

The authors also provide a very useful review of the types of things within microbial and human cells that may be responsible for harvesting natural sunlight or light provided as therapy.

Why is the paper interesting?

I enjoyed this paper because it provides an overview of an area that I am not familiar with, namely light therapy, its effects on the microbiome, and potential applications to treating human ill-health. The paper provides many citations for its observations and claims which I can follow up with to understand more.

Access to the background literature is important because I did note that some of the claims they make in relation to the human microbiome (an area I am reasonably familiar with) are not well supported. Either that or their manuscript review and edit process was poor. I came to this conclusion from the following mistakes in the paper:

  • Human Microbiome – conflate microbiome and microbiota

  • Human Microbiome – omit fungi from a list of microbiota that included only bacteria, archaea, protists, and viruses (debatably not microorganisms)

  • Human Microbiome - give credence to the (erroneous, in my opinion) belief that the gut microbiome is an organ

  • Microbiome and Human Disease – describe trimethylamine oxide (TMAO) as being causal in the development and progression of heart disease (atherosclerosis). This is (in my opinion) unproven, contentious, and it is often used by vegan and vegetarian diet proponents to label animal-based diets as unhealthy

  • Microbiome and Human Disease - use the acronym TMOA rather than TMAO, which points to poor review and editing

  • Potential Applications to Human Disease – describe irritable bowel disease as an area of research. The two bowel-related pathologies typically described are irritable bowel syndrome (IBS) and Inflammatory bowel disease (IBD)

 

How does the paper help me to understand health and longevity?

Since 2017 I’ve been focused on the effect of diet on my health and have summarized what I’ve learned in my blog Eating Myself Healthy. I eliminated seed oils from my diet and found that I did not develop sunburns the way I had when I was younger. That discovery led me to seek more natural sun exposure and to investigate the potential benefits I might experience if I managed my exposure properly. However, until I found this paper, I was still pretty unclear about the effects of light on the human microbiome.

This paper begins to fill the gaps in my knowledge of the impact that light (natural or artificial) can have on my microbiome and how that might come about. It also introduces me to the new term “photobiomics” which describes the combined effects of light therapy on microbiota, microbial metabolites and their interaction.


Study outline

This is a review publication. It summarises what the authors discovered about effects of light on the microbiome after conducting a search of the published literature.

References

  1. Liebert A, Bicknell B, Johnstone DM, Gordon LC, Kiat H, Hamblin MR. "Photobiomics": Can Light, Including Photobiomodulation, Alter the Microbiome? Photobiomodul Photomed Laser Surg. 2019 Nov;37(11):681-693. doi: 10.1089/photob.2019.4628. Epub 2019 Oct 9. PMID: 31596658; PMCID: PMC6859693

Michael Butler
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