Dr. Michael Ruscio, DC is a clinician, Naturopathic Practitioner, clinical researcher, author, and adjunct professor at the University of Bridgeport. His work has been published in peer-reviewed medical journals and he speaks at conferences around the globe.
Sun exposure is absolutely necessary for human health, including your gut.
While burning from the sun can increase risk of skin cancer, consistent, moderate, non-burning sun exposure is good for you and actually decreases the risk of many types of cancers.
Benefits of sun exposure for gut health include increased vitamin D production, modulating the immune system, and positively shifting your gut microbiome.
You can “build up” your sun exposure during the spring and summer months, but red light therapy and vitamin D supplementation may be helpful stand-ins during the winter.
With mindful sun protection and exposure, there’s no reason to fear the sun — in fact, it can be wonderful (and free!) health tool.
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 that sun exposure can benefit your gut, 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 .
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 .
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 .
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) .
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 . 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 .
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 . 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 
Prostaglandin E2 formation, which may improve immune function 
Suppression of the immune system, which may be helpful in autoimmunity but may inhibit acute immune responses 
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 , all-cause death , type 2 diabetes , and Parkinson’s disease .
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.
How Sun Exposure Helps Your Gut
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 . 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 .
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 .
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 . 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 .
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.
Supports a healthy immune system and modulates autoimmunity [21, 22]
Lowers inflammation and may improve the progression of inflammatory diseases 
All of these effects make vitamin D a powerful therapeutic tool for gut conditions of all kinds . 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 .
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.
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