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Evidence Based

This article is based on scientific evidence, written by experts and fact checked by experts.

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This article contains scientific references. The numbers in the parentheses (1, 2, 3) are clickable links to peer-reviewed scientific papers.

How to Use the Power of Sun Exposure for Gut Health

Written by Dr. Ruscio on August 22, 2023

Written by Dr. Ruscio on August 22, 2023 — Reviewed by Aimee Gallo

Don’t Fear the Sun, Use it to Your Advantage

• Consistent Moderate Sun Exposure is Good for You|
• Sun Exposure Benefits|
• Sun Exposure and Your Gut|
• Sun-Gut-Immune Connection|
• Vitamin D for Gut Health|
• Healthy Sun Exposure Routine|
• Respect, Don’t Fear, the Sun|

Do you notice that you feel better during the summer when you have more consistent sun exposure? Turns out that’s not just a coincidence: the sun is good for your health, specifically your gut health. This connection might come as a surprise, but there’s good research to show the benefit of sun exposure for gut health, whether you have a chronic GI condition or are looking for more general gut support. 

In this article, I’ll look at the various ways that sun exposure can benefit your gut health, how to get safe, moderate sun exposure, and a few tips to keep in mind as you start to make regular sunshine a more consistent part of your daily routine. 

Consistent Moderate Sun Exposure is Good for You

Let’s debunk one of the biggest myths in modern health history: the sun is not inherently bad for your health. Yes, overexposure to the sun and burning your skin is associated with an increased risk of skin cancer, but research shows that regular, moderate, healthy sun exposure is actually associated with a decreased risk of skin cancer (melanoma) or had no effect at all [1]. 

Chronic sun exposure is also associated with a reduced risk of colorectal, breast, and prostate cancer and non-hodgkin’s lymphoma, partially related to vitamin D production, but also due to other pathways including immune system modulation and circadian rhythm regulation [2]. 

Other research identifies insufficient sun exposure as a “significant public health problem,” citing increased incidences of cancer, metabolic disease, multiple sclerosis, Alzheimer’s disease, type 1 diabetes, and asthma as possible effects [1]. 

Ultimately, humans are creatures of the sun. Long before we were building homes and cities and living largely indoors, we lived outdoors and were exposed to the sun every single day. While it pays to be mindful of how much sun we expose ourselves to, there’s no denying that it plays a key role in our mental and physical health. 

Sun Exposure Benefits

The main benefit of sun exposure is getting enough vitamin D, which is actually synthesized in our skin when our skin is exposed to sunlight. Although we have vitamin D supplements these days, obtaining vitamin D from regular, healthy (non-burning) doses of sunshine may be the optimal way to get most of our vitamin D requirements. Unlike oral vitamin D supplements, vitamin D made from sunlight cannot reach toxic levels in the body (although you’d have to be taking a lot of vitamin D for a long time for that to happen) [3].

One meta-analysis found that exposing about 10% of the body to moderate doses (depending on skin phototype) of sunlight is enough to keep your vitamin D levels healthy and stable [4]. However, the amount of time each person should expose their skin varies depending on skin color, time of year, time of day, and location. People with darker skin require more time than those with lighter skin to get the vitamin D they need [5].

Why do we need vitamin D? Vitamin D regulates calcium and phosphorus absorption in the gut and helps the kidneys reabsorb these minerals to maintain healthy bones and muscles. Vitamin D also helps with insulin production, heart contractions, immune system function, and preventing inflammatory bowel diseases [6]. We’ll expand on the benefits of vitamin D for your gut a little later.

Although vitamin D production is the most established benefit of exposing the skin to UV light, other potential benefits of sun exposure include:

• Nitric oxide production, which may improve cardiovascular health [7]
• Prostaglandin E2 formation, which may improve immune function [7]
• Suppression of the immune system, which may be helpful in autoimmunity but may inhibit acute immune responses [7]
• Reduction of high blood pressure [8]
• Circadian rhythm regulation [9, 10]
• Improved sleep quality [10]
• Decreased depression and anxiety [10, 11, 12]
• Improved cognitive function [11, 12]

Though we can’t draw a causal relationship from them, systematic reviews of observational data have found that sun exposure is associated with a lower risk of cardiovascular disease [8], all-cause death [8], type 2 diabetes [13], and Parkinson’s disease [14].

As long as you’re aware of your time in the sun, there are many health benefits to sun exposure on a daily basis, even if you’re only outside for a short time. 

Sun Exposure for Gut Health: How It Helps

There are a few different ways healthy sun exposure can support your gut health. One is by improving the composition of your gut microbiome [15, 16, 17]. 

In a small observational study, women with low vitamin D who were exposed to UVB light three times in one week had both significant improvements in vitamin D levels and changes to their gut microbiota [15]. Their microbial changes were reminiscent of microbial compositions in hunter-gatherers who are regularly exposed to sunlight, supporting the notion that sun exposure can affect the microbiota [16]. 

Another literature review illustrated the connections between skin conditions, the immune system, and the gut microbiome. They found that exposing the skin to UVB to increase vitamin D levels can increase the diversity of the gut microbiota, and in psoriasis patients can change the skin microbiota as well [17]. 

We need more research on the effects of sunlight on the microbiome, but it’s worth being intentional about your sun exposure if you’re trying to improve your gut health. 

Alongside improving the microbiome composition, sunlight affects serotonin production, a neurotransmitter that is primarily made in the gut and modulates proper gut function and motility [18]. If low serotonin levels are contributing to poor gut function, it’s likely that sun exposure would be helpful. 

The Sun-Gut-Immune Connection

Sunlight exposure can also modulate the immune system. Both UVB exposure and UVA radiation from sunlight can suppress the immune system, which may benefit those with autoimmunity, including inflammatory bowel disease [7].  

Yet sun exposure may also increase immune activity by increasing vitamin D levels [19, 20]. So there is likely some balance struck here between these immunosuppressive and immune-boosting effects that help the immune system regulate itself. 

Vitamin D for Gut Health

Vitamin D has huge benefits for gut health, and while we can supplement vitamin D for this purpose, there are certain added benefits to getting your vitamin D the all-natural way, from sunlight on your skin. 

Vitamin D: 

• Supports a healthy immune system and modulates autoimmunity [21, 22]
• Supports a healthy gut barrier [21]
• Modulates the gut microbiome [21, 23]
• Improves symptoms of IBS [24]
• Lowers inflammation and may improve the progression of inflammatory diseases [25]

All of these effects make vitamin D a powerful therapeutic tool for gut conditions of all kinds [26]. While supplementation may be warranted in some cases such as ulcerative colitis or severe leaky gut, sun exposure can provide healthy vitamin D synthesis while ensuring that toxicity never becomes an issue [27]. 

Making Healthy Sun Exposure Part of Your Routine

So you’re ready to make healthy sun exposure a consistent part of your daily life. How should you start? 

This depends on a few factors, including where you live (closer or further from the equator), your skin tone, and the season. But here are some general tips:

• Start out by exposing yourself to early morning or late afternoon sun for just 5–10 minutes at a time. (These times are also ideal for using the sun to regulate your circadian rhythm!)
• If you have a darker skin tone, you may be able to handle more sun exposure at first, but still build up your sun tolerance over time.
• Use protective clothing and hats so that only some of your skin is exposed to the sun, as opposed to a bathing suit where nearly all of your skin is exposed.
• If you’re planning on being out in the sun longer than 15 minutes, wear protective clothing or apply mineral sunscreen.
• Remember that any skin type can burn in the sun, and you often won’t notice the evidence on your skin until later. If you feel like you’re burning, cover up or find shade.
• Build up longer exposures as you start noticing your skin tanning (if you are able to tan). 
• Consume foods with plenty of antioxidants (aka colorful fruits and vegetables) that can protect against sun damage.
• Use the D minder app to calculate your vitamin D absorption and gauge a healthy amount of sun exposure based on your location, season, skin exposure, and other variables.
• Enjoy the sunshine and keep track of any energy, sleep, immune or mood benefits you notice!

Getting healthy sun exposure can really change your health for the better, including your gut health. Plus, it’s free, and we can often combine it with other healthy habits, such as exercise or meditation. Don’t underestimate the power of sunshine!

How to Get Some of the Benefits of Sun Exposure During the Winter

For many of us, our energy, mood, and maybe our digestive health can take a hit during the winter months, and part of the reason behind that is less sun exposure. So what can we do to limit those effects?

There is some research that shows that building up to longer exposures during the spring and summer months can ensure that your vitamin D levels remain healthy throughout the winter months despite getting less daily sun exposure [28, 29]. Studies suggest exposing (without sunscreen) 35% of your skin (face, hands, forearms, lower legs) to midday sunshine every day from March to September. 

However, this still might not be enough for some people, or they might find this difficult to keep up with every day. In that case, supplementing vitamin D in the winter can be helpful as a precaution against vitamin D deficiency. Just make sure to test and see where your levels are before starting daily supplementation. 

Another potential strategy to use during the winter is red light therapy. Red light therapy (also called low-level light therapy or photobiomodulation) has been shown to improve mood, energy, skin health, and more, somewhat similarly to sun exposure [30, 31, 32]. It may even protect against neurodegeneration and decrease pain [33, 34, 35]. All things considered, red light therapy is worth looking into as a wintertime substitute for healthy sun exposure. 

Respect, But Don’t Fear, the Sun 

The sun is a powerful force, but we don’t need to hide from it to protect ourselves. In fact, we need some amount of sunshine to keep us healthy and energized — including our gut health. The fact that sun exposure is our primary source of vitamin D is proof enough that it’s absolutely necessary for human health. The trick is to build up your tolerance to the sun over time and use protective clothing and sunscreen as necessary. 

Want to learn more about gut health and gut-healing strategies? Check out my YouTube channel for all the latest gut health news explained in a way you can actually understand. Or you can check out my book Healthy Gut, Healthy You for a full gut healing protocol covering diet, lifestyle, stress, exercise, sleep, and more.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.