Want to feel more comfortable at altitude? Take a look at your gut health.

One afternoon in August 2024, high in California’s White Mountains, Tatum Simonson, an associate professor at the University of California, San Diego, and a physiologist with expertise in advanced adaptation, and her volunteers limped into Barcroft Station. This off-grid research outpost is located at 12,470 feet above sea level, surrounded by jagged peaks and rugged scree slopes along the eastern edge of the Sierra Nevada. Within hours of arrival, some participants felt the physical impact of arriving in the high-altitude laboratory. A throbbing headache, creeping nausea, and trouble sleeping are all telltale signs of altitude sickness (which happens when you gain altitude too quickly without giving your body enough time to adapt to the decreasing amount of oxygen in the atmosphere as you rise).

For decades, mountaineers have relied on slow climbing and a prescription drug called acetazolamide, sometimes known as Diamox. But Simonson wondered if they were overlooking another factor: the gut.

Bacteria, fungi, and other microorganisms make up about half of the cells in our bodies, and some estimates suggest that they outnumber our genes by about 100 to 1. The lack of oxygen at high altitudes can also stress your gut microbiome, which can change the way your body senses and responds to hypoxia.

“Gut bacteria are constantly sending signals to each other and to cells in the body, and some of these signals go far beyond the gut to the brain,” Simonson said. outside.

When Simonson experienced the stress of altitude sickness, he thought: Could these signals help explain why some people feel sick at high altitude?

What are the stages of altitude sickness?

• There are three stages of altitude sickness.
  1. Acute altitude sickness: the most common and mildest form
  2. High altitude pulmonary edema (HAPE): It occurs when the lungs begin to fill with fluid. This requires prompt medical attention
  3. High altitude cerebral edema (HACE): A very severe form of altitude sickness that causes swelling of the brain and requires immediate medical treatment.
• Without treatment, HAPE can be fatal within 12 hours, and HACE can be fatal within 24 hours.
• To acclimate safely, climb slowly (no more than 1,000 feet per day) and stay hydrated. Also, if you are a big coffee drinker, don’t stop drinking coffee. Otherwise, you may experience caffeine withdrawal and feel unwell. It can also be difficult to differentiate between caffeine-related headaches and headaches caused by high altitude.

Simonson’s curiosity about high-altitude physiology led him to the Tibetan Plateau 15 years ago. She was conducting fieldwork in Madu County, Qinghai Province, at an altitude of 14,241 feet, scanning the genomes of Tibetans, Han Chinese, and Japanese people to understand how Tibetans had adapted to life at high altitude. There, she experienced first-hand the effects of altitude on the body. “I was trying to lift heavy equipment at a small village hospital and the height was breathtaking,” she recalls. She was told to take Diamox, but the temporary tingling in her hands, a common side effect of the drug, was unpleasant.

Simonson began studying the genetics of the Tibetan population, which had lived at extreme altitudes for thousands of years. Over time, she expanded her research into the Andes Mountains, incorporating the microbiome (all the bacteria, fungi, and other microorganisms that exist on and within the human body) into her research, and collecting stool samples from high-altitude communities.

The gut microbiome influences digestion and immunity, and may even be linked to mental health. With this knowledge, Simonson’s question changed to: can she? affect a person’s microbiome How to withstand high altitudes?

Effects of low oxygen at high altitude on the intestines

Even the most hardy climbers can suffer from altitude sickness. Almost 80% of people who develop acute mountain sickness experience at least one gastrointestinal symptom. This is because gut bacteria change at high altitudes due to lower air pressure and oxygen levels. This type of intestinal problem is called high-altitude flatus. Diarrhea is commonly reported among Everest climbers, and nausea and vomiting are frequently observed in high-altitude climbers even when clean water is available.

For mountain guide Emily Drinkwater, these symptoms are all too familiar. Drinkwater has been guiding professionally since 2001 and is the ninth American woman to earn IFMGA certification, the highest certification a professional mountain guide can earn. She guides heli-skiing in Utah in the winter, alpine climbing in Wyoming in the summer, and has made first ascents in Alaska, the Karakoram Mountains, and the Hindu Kush Mountains. “My body doesn’t feel good at high altitude,” she says. “The number one symptom is nausea and the inability to eat much after 15,000 feet. I’ve always attributed this to intestinal hypoxia (lack of oxygen in body tissues). Other symptoms include deep fatigue, headaches, and lack of sleep.” She manages her headaches and sleep deprivation with hydration and Diamox, but nothing seems to alleviate her nausea or loss of appetite, and she reports losing weight on long expeditions.

One possible explanation for nausea and loss of appetite may be disruption of the intestinal barrier, the lining of the intestines that seals out bacteria and their byproducts. At high altitudes, that barrier can be weakened.

“When the body becomes hypoxic, the intestinal barrier begins to ‘break down’ and small pieces of bacteria can enter the bloodstream and interact with the immune system, causing inflammation,” says Zach McKenna, assistant professor of exercise science at the University of Arkansas. McKenna studies the effects of altitude and other environmental stressors on the intestinal barrier, but was not involved in Simonson’s research.

The brain, on the other hand, reacts to the drop in oxygen by acting as a control center, sending signals to the body to breathe faster and deeper at higher altitudes. But the gut may also be sending signals to the brain through the gut-brain axis, a bidirectional network of neural, hormonal, and immune signals. Keeping your gut healthy with probiotics may help support these signals.

Still, experts say there are still many mysteries about the gut. “We don’t fully understand what causes gastrointestinal distress during high-altitude exposure,” McKenna added. “Reasonable causes include oxidative stress (cell damage), damage to the microvasculature (blood vessels), and intestinal barrier dysfunction. These are all related to low oxygen levels and how blood is redistributed from the intestine during exposure to high altitudes and during activity and exercise.”

If so, could probiotics help?

Climber tests probiotics in high-altitude laboratory

To test this idea, Simonson and her team took 17 volunteers to Barcroft Station, an ideal high-altitude laboratory, to see how probiotics affect oxygen levels, sleep, and gut-brain signaling under real-world conditions. Study participants were given either a probiotic containing multiple bacterial strains or a placebo up to three times a day before and during the climb.

“Within a few hours and over the next few days, we measured their oxygen saturation levels,” he says. “Those who took probiotics had higher oxygen saturation and felt better overall. They maintained high oxygen levels during sleep, even though sleep is often disrupted at high altitude.” Simonson says these findings are important because “these results suggest that there are signals that travel from the gut to the brain that may help trigger these responses.”

The survey results were published in a magazine iscienceit’s still early, but it’s reassuring. Professor Simonson says this study is exploratory and future studies will test different probiotic strains and timing during trekking to assess how the gut responds at high altitude. “Responses to probiotics may vary from person to person, and long-term studies with large groups are needed,” she added.

“This study shows some promising results,” McKenna said. He agrees that Simonson’s study needs to be replicated in larger groups and with more direct measurements. “Although the relationship between intestinal barrier function and acute mountain sickness is not fully established, probiotics may offer benefits in a number of ways,” he says.

For example, a study published in 2025 by the journal Frontiers of nutrition This suggests that probiotics may help protect cells from oxidative stress. Other recent studies have shown that probiotics may help reduce cognitive decline in people with neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease.

What does the future of gut microbiome research mean for climbers?

If the gut plays a role in coping with high altitude, it could have major implications for mountain safety. Maintaining good judgment can be the difference between a safe expedition and a dangerous one. “I have to be capable, competent and strong enough to continue to make good decisions and manage risk for myself and my team,” says Drinkwater. “We will prioritize proper acclimation, hydration, and rest to get through this.” She also checks in with team members regularly to see how they’re feeling.

Understanding how probiotics and the gut influence altitude sickness is an exciting frontier that has the potential to redefine our knowledge of the trillions of microorganisms in our bodies and how their relationships change at high altitude, scientists say.

When asked if she takes probiotics herself, Simonson laughed and said, “I definitely do.” And since altitude affects my husband even more, I made sure to have him take the altitude as well, just to be safe.

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