It's the dead of winter, so in most parts of the country, the cold, windy, icy outdoors might be the last place you want to be right now. But, you should probably bundle up and head out anyway, especially if you're trying to avoid catching another nasty cold. Okay, but why?

Turns out, the simple act of just being outside is good for your gut—and what's good for your gut is also good for your immune system. Many of us may think that the best thing we can do for our gut is to eat nutritiously. And while that's true, there are other things we can incorporate into our daily routines to boost our gut and immune health.

Take it from one of our experts. "I tell people to walk outside every day," says Supriya Rao, M.D., a gastroenterologist with Tufts Medicine in Boston, Massachusetts.

So, if you're wondering how exposure to the outdoor world can affect what goes on deep inside your GI tract, see what our experts have to say. They'll discuss how the two are connected, and what you can do right to give your gut—and immune system—the boost it needs.

How are gut health and the immune system related?

If you've opened up your phone and read even one article about health in the past couple of years, you may have noticed that there's been an emphasis on gut health. Newer research has shown that your gut microbiome (aka the microorganisms, such as bacteria or fungi, that live within your digestive system) can affect other body functions too, such as your overall mood, your likelihood of experiencing allergies, and yes, how often you get sick.^1,2

A whopping 80 percent of your immune cells live inside of your digestive system, and having the right balance of good-to-bad bacteria can influence how your body responds to germs and other foreign invaders, according to a review published in the journal Nutrients.³ In short, "if your microbiome isn't healthy, you won't be healthy either," Dr. Rao explains.

Why being outside is good for you

Exposure to the outdoor world seems to influence that balance of good and bad bacteria. And as a result of that balance, your body can support a stronger immune system and reduce inflammation, per a review published in the International Journal of Environmental Research and Public Health.⁴ What exactly about being outside can help your gut is still being explored, but experts believe there are a few different things going on here.

First, hanging out in nature exposes you to different kinds of bacteria. When you go outside, you're breathing in some of the microbes that live in the surrounding soil and greenery, according to the Environmental Protection Agency (EPA). Your local park or backyard totally counts here, btw. You don't have to trek out to a remote forest, Dr. Rao says.

Research backs this up. One study published in Science of the Total Environment found that those with a higher number of shrub species in their backyards had stool samples with a healthier balance of bacteria.⁵ Touching plants or dirt on your hands seems to make a difference too, according to a study published in Microbiologyopen.⁶ (Makes you want to go pick some flowers, doesn't it?) 

Being outside seems to improve the diversity—and strength—of your own microbial community, which in turn may bolster your body's ability to fight germs, says Elena Ivanina, M.D., a board-certified gastroenterologist based in New York City. 

But that's not all. While some studies show that exposure to the outdoors improves your gut bacteria, being outside can also help your mental health—which plays an important role in your overall immunity, too. Spending time in nature is a really good stress reliever, and low stress levels keep your microbiome happy. "Being in nature is key to a balanced nervous system and a healthy, diverse mut microbiome," Dr. Ivanina says.

And the research supports this, too. One study published in Scientific Reports recruited 54 preschoolers for a 10-week, nature-based play program and found that the increased outdoor time was tied to lower levels of perceived stress and anger among the kids. They also noticed higher levels of healthy bacteria and the feel-good neurotransmitter serotonin in their stool samples.⁷

So, how much time outdoors do you need?

It's still too early to say exactly how many minutes you need to log in the park to reap gut- and immune-boosting benefits. Chances are just getting out for a stroll every day will make a difference, Dr. Rao says. 

Dr. Ivanina agrees that any amount of outside time you can get is a good thing. If you can get some sun exposure and allow your bare feet to touch the ground (when it's warm enough), even better. "Grounding and actually touching the earth with your body has been shown to alter pain perception and affect the immune system," she explains. (Just remember to wear sunscreen on those especially hot days!)

If you're pressed for time, make it a point to move your workout outside whenever you can. Regular exercise is another stress-buster with major benefits for your gut microbiome.⁸ So you're really getting a bang for your buck when you combine the two.

Since this is probably one instance where more is generally better, think about other points in your day where you can sneak in a nature break. Could you have coffee on your porch or stoop in the morning instead of in front of your phone or laptop? How about a quick walk during your lunch break? Whatever time you can squeeze in can be beneficial for your well-being, in more ways than just one.

Other ways to boost gut health

While we're talking about doing good by your gut, your gears might be turning over whether there are other things you can do to make your microbiome happy. Here are a few things to keep in mind:

• Get enough sleep: People who get enough shuteye tend to have more diverse (read: healthier) microbiomes compared to those who are chronically sleep-deprived.⁹ Logging at least seven hours of sleep per night makes a huge difference in your ability to cope with stress—and keeping your stress levels in check is a big deal for gut health, Dr. Rao notes.  
• Eat a healthy diet: Fiber-rich foods like fruits, veggies, whole grains, nuts, and beans are packed with prebiotics, which feed the microbes in your gut. Fermented foods like yogurt, kimchi, and sauerkraut add even more good bacteria. But, processed and sugary foods are like fertilizer for unhealthy bacteria, so they can send things out of whack.¹⁰ So, next time you're at the grocery store, pick up a new gut-healthy food to try.
• Start doing a mind-body practice: Think yoga or meditation. They're known stress relievers, "and they're also a key to gut and immune health," Dr. Ivanina says. One study on Tibetan monks found that regular meditation may help regulate the gut microbiome and potentially lower the risk for chronic health conditions and depression.¹¹
• Stay hydrated: If you need another reason to drink enough fluids, here it is: Low-water drinkers may have higher levels of unbalanced gut bacteria compared to those who sip frequently.¹²

The bottom line

Getting some fresh air can shift your gut health for the better, by improving your microbiome's diversity and reducing your stress. And that in turn might help you get sick less often. Sounds like a win-win to us. And the best part? It's an easy (and free!) way to take care of your body and mind. So, what are you waiting for? Grab your keys and get outside.