Tummy Troubles Up High: How Altitude Affects GI Physiology

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If you’re planning a spring skiing vacation or a summer of hiking in the mountains, you might want to prepare your mind and body for the physiological effects of high altitude.

At altitude, the air pressure is lower. The amount of oxygen in the air is the same as sea level (about 21%), but less oxygen is able to bind to proteins in your blood and get into your cells. This leads to conditions called hypoxemia—when your bloodstream can’t get enough oxygen to deliver to your cells—and hypoxia—when your body is low on oxygen and may not be able to function properly.

Hypoxia and hypoxemia are two of the main culprits behind a condition known as acute mountain sickness, or “altitude sickness.” Symptoms can include diarrhea, nausea, loss of appetite and vomiting and are thought to be due in part to hypoxia. But these stomach aches and pains may also be caused by how high altitude affects your gastrointestinal (GI) tract.

Epithelial cells line your GI tract to form what is known as the intestinal barrier. Under normal conditions, your intestinal barrier helps transport nutrients and prevents toxic and harmful bacteria from moving across the intestinal wall. This barrier is the “bouncer” who “IDs” everything going in and out of your GI tract. It also regulates your immune system to respond to stress and damage.

Altitude impairs many of these functions. The low oxygen conditions create an acidic, energy-depleted environment that damages intestinal barrier cells and opens up the tight junctions that hold these cells together. This damage causes toxins to cross the barrier into your circulation. Sometimes this damage is called a “leaky gut.” Hypoxia also increases levels of inflammatory proteins that can damage the intestinal barrier.

Interestingly, exercise may make these conditions worse. This is not a good scenario since many people who go to regions of high altitude do so to ski, hike, rock climb or mountaineer, among other high-exertion activities. Studies have shown that exercise during hypoxia can aggravate intestinal barrier dysfunction and inflammation. This may explain why people who attempt to climb Mount Everest experience a lot of digestive problems.

Is there a solution to these tummy troubles, other than staying at sea level? Perhaps. Some types of medications that are used for altitude sickness may reduce symptoms by helping prevent intestinal barrier dysfunction and inflammation. There is also some evidence that some nutritional supplements, including curcumin, could help relieve altitude-related GI symptoms.

“Extreme physiology” can help us learn a lot about how to optimize health and performance in unique and stressful environments. As we continue to explore even more extreme “altitudes” in space, we will rely on knowledge gained from this science to help us accomplish increasingly impressive feats of humanity.

Brady Holmer

Brady Holmer is a PhD student in exercise physiology at the University of Florida. His lab focuses on cardiovascular physiology, mainly how exercise can play a role in health, disease and aging. Holmer hosts a podcast called “Science & Chill,” where he sits down with scientists in the fields of physiology, biology, health and nutrition to discuss their work. He served as a meeting blogger for the American Physiological Society’s 2021 annual meeting at  Experimental Biology.

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