Gut health benefits of Sun exposure

Despite evidence of gut health benefits of Sun exposure, we’re told to avoid Sun exposure. Ultraviolet rays from the Sun are a carcinogen they say, so it’s best to stay away as much as possible. But there’s more to it than that.

We’ve known for years that less Sun exposure on the skin increases IBD prevalence and severity. Studies also show that greater exposure to sunlight reduces the risk of surgery for people with Crohn’s disease.

Now, I know what you’re thinking, vitamin D, right? Well, it turns out exposing your skin to the Sun has benefits caused by vitamin D, and some that are not. So, it’s not just about vitamin D.

But do you know the worst part about all of this? Sunscreens don’t appear to reduce your risk of Skin Cancer either.

Sunscreen and Skin Cancer Risk

A Cochrane Review in 2016 found that daily sunscreen use does not protect against basal cell or squamous cell carcinoma. The only quality study found no benefit to sunscreen use for the 2 most common types of Skin Cancer.

A more recent review conducted in 2018 found that sunscreen use neither protected against Melanoma nor non-Melanoma Skin Cancer. Neither of these studies show that it’s perfectly safe to be out in the Sun willy-nilly. Skin Cancer is a real concern and does kill people.

But, it’s estimated that 7,230 people will die of Skin Cancer in 2019. To put that into perspective, 840,768 people died of cardiovascular disease in 2016. In a recent review, greater Sun exposure decreased blood pressure in 3 out of 4 studies in the short term. There was also a decrease in cardiovascular disease mortality in 5 out of 6 studies.

This is not only problem for cardiovascular disease but it may be problematic for gut health. As it turns out, broad spectrum sunscreens block 2 of the most important types of light for setting the skins circadian rhythm. I’m talking about ultraviolet A and ultraviolet B radiation.

Sun exposure and dying early

Several recent studies have also looked at a person’s Sun exposure and dying early. The most recent found that women with the greatest Sun exposure tended to live 1-2 years longer than those with the least. And this is the same general trend for all of the most recent data.

I don’t want to downplay the risk of Skin Cancer, but the data seems to be very clear. Completely avoiding the Sun seems to be worse for you than actively exposing yourself to the Sun. But we know ultraviolet light exposure is a human carcinogen, so doing it safely is important.

However, while being in the Sun increases your Skin Cancer risk, it decreases your risk for Breast Cancer, Prostate Cancer, non-Hodgkins Lymphoma, and Colorectal Cancer. The association of Sun exposure with IBD and Colorectal Cancer begs the questions: are there gut health benefits to Sun exposure?

Gut health benefits of Sun exposure

Given the relationship between Sun exposure, IBD, and Colorectal Cancer, are there benefits of Sun exposure to the gut? Vitamin D seems to be one of the drivers of the protective effect. But is supplementing with vitamin D the same thing as making it from the Sun?

Vitamin D obtained from dietary supplementation affects the gut differently than vitamin D from Sun exposure. In a study in mice, vitamin D from ultraviolet radiation decreased inflammatory markers(IL-1b & IL-17) and yielded a different microbiome than mice given vitamin D in their diet.

The study also found beneficial effects of Sun exposure independent of vitamin D. This primarily lowered inflammation, decreasing IL-1b by 5-fold. Thus, there may be significant drawbacks to avoiding exposure to the Sun that supplemental vitamin D can’t fix.

Other evidence shows exposing mice to ultraviolet B(UVB) radiation induces the aryl hydrocarbon receptor(AhR) in the skin, blood, and gut. AhR is important for detoxification and inhibiting inflammation. It has also been shown to prevent leaky gut and act as a communication hub between the microbiome and gut.

One final study found that irradiating the eye of mice increased IL-10 and immunoglobulin A(IgA) in the intestine. IL_10 is an anti-inflammatory cytokine and IgA helps protect the gut. These effects were caused by activation of the HPA axis and cortisol release.

Circadian rhythms, gut health, and Sun exposure

The benefits of Sun exposure to the gut are undoubtedly related to circadian rhythms. Being exposed to the Sun is one of the important ways we set our circadian rhythms. While we focus on Sun exposure to the eye, exposing the skin to the Sun also helps set our circadian rhythms.

We tend to focus on visible light exposure to the eye as it pertains to circadian rhythms, but the skin is important too. I covered this lesser known aspect of circadian rhythms in a video titled Health Benefits of Exposing your Skin to Sunlight. In it I cover:

  • The best times to get Sun exposure
  • How to safely get adequate Sun exposure
  • The benefits of different types of solar radiation
  • How Sun exposure to the skin fits in to circadian rhythms

There’s a lot of data out there detailing how circadian rhythms improve gut health. But most articles on circadian rhythms focus on blue light and time-restricted eating. And while these 2 factors are important, there’s a lot more to circadian rhythms.


Health authorities have done a good job of scaring us away from Sun exposure. Until the last decade or so, no one thought to ask if there are any negative effects to completely avoiding the Sun. Now, data is showing that there may be some negative effects to inadequate Sun exposure.

Granted, a lot of this data is epidemiological or in mice. But when the epidemiological data jibes with the data in mice, it’s time to begin paying attention. Some of the strongest data links Sun avoidance with a greater risk of IBD and Colorectal Cancer.

Inflammation is a driver of both diseases and Sun exposure appears to lower inflammation in mice. So maybe it’s time to revisit the Sun exposure guidelines. It appears that there may be significant benefits of Sun exposure to gut health that need attention.

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