Whether it's a wintry visit to a snow-covered ski resort or a summertime hike in an alpine park, a vacation in the mountains can be breathtaking. Literally.
"There is less oxygen available to breathe at higher altitudes," said Dr. William K. Cornwell, an associate professor of cardiology at the University of Colorado Anschutz Medical Campus in Aurora. "And if you are not healthy, or if you have risk factors for heart disease or stroke, then the higher you go, the risk may be higher of something going wrong."
But don't rebook that mountain adventure for something at sea level just yet. With a little planning – and building in time for your body to adapt – you may be able to reduce the risks of altitude-related problems.
That preparation starts with being aware of how your body reacts at higher elevations. Visitors who travel by plane can zip from low to high altitudes without being fully aware of the differences, said Dr. Jennifer Dow, who practices emergency medicine at Alaska Regional Hospital in Anchorage.
"They don't have their ears popping as they go up through multiple passes," said Dow, a past president of the Wilderness Medical Society. "They don't see the signs on the road indicating that they're at a higher altitude.'"
The differences might not be visible, said Dow, who started working with the National Ski Patrol in California as a teenager, but there's definitely something in the air. Technically, the atmosphere is always about 21% oxygen. But as you climb, air becomes less dense, which means you inhale fewer oxygen molecules with each breath.
As calculated by the Center for Wilderness Safety, at 5,000 feet (not quite the altitude of Denver International Airport), you'll be breathing air that feels as if it's only 17.3% oxygen. At 10,000 feet, the altitude of the summit that skiers would experience at many Rocky Mountain resorts, it's the equivalent of 14.3% oxygen. And for hikers at the 20,308-foot summit of Alaska's Denali, it's the equivalent of only 9.7% oxygen.
Lower air pressure makes it harder to push oxygen molecules through the lungs. According to a 2021 American Heart Association scientific statement that Cornwell led on exercise at high altitudes, the body's maximum ability to take in oxygen drops around 1% for every increase in altitude of about 330 feet above 4,900 feet.
The body reacts to the lower oxygen availability in many ways, said Cornwell, which is not a surprise when you think about how much of the body is dedicated to processing it.
"You have to breathe oxygen into your lungs," he said. "It has to go into the bloodstream. Your heart has to pump oxygenated blood through blood vessels, get it to the muscle, and then the oxygen has to be absorbed from the blood vessels into the muscle and transported into the mitochondria," the cellular workhorses that use oxygen to make energy.
Reduced oxygen levels trigger the sympathetic nervous system – the "fight or flight" response. "That in and of itself puts additional stress on your cardiovascular system," Cornwell said. Your heart beats faster. Your breathing rate increases. Blood pressure may initially drop as a result of the reduction in available oxygen, which can cause people to faint.
Somebody with risk factors for heart disease who immediately starts skiing, snowboarding or hiking on arrival would be straining an already-stressed system even more.
For people with existing heart conditions, the effects can be serious. According to the 2021 scientific statement, low levels of oxygen in the body at higher altitudes can trigger problems such as chest pain for people with coronary artery disease or worsening symptoms for people with heart failure, a condition where the heart does not pump blood effectively. Sleep apnea, which is linked to an increased risk of heart disease and stroke, can worsen.
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And sudden cardiac death is the most frequent, nontraumatic cause of death at altitude: More than half of these events occur on the first day at high altitude. That risk can be limited if visitors take time to acclimate, Cornwell said.
The 2021 statement defines "high" altitude as above 9,840 feet. But Dow said there is no hard line on when altitude issues might kick in. As she spoke to American Heart Association News, she was in Lake Tahoe in California, training Air National Guard rescuers about altitude, hypothermia and cold injury. Lake Tahoe sits at a relatively modest 6,200 feet, but she was still feeling an altitude-related lack of energy and endurance.
People who live at relatively high altitudes shouldn't feel immune to problems, Cornwell said. "In Denver, we're not really in the mountains. We're higher than sea level, but we're still not that high." Someone living at such heights might be slightly more acclimated than somebody from Boston or Dallas, but going to a lower-oxygen environment to do intense activity would pose some of the same concerns, he said, especially for somebody who is usually inactive.
Cornwell drew a parallel to somebody at any altitude shoveling snow after a blizzard. "Shoveling snow is exercise, so if you're not exercising routinely and you go outside on a cold day lifting heavy weight for 20 to 30 minutes, you're placing an incredible amount of demand on your heart. If you have risk factors for heart disease, then this sudden increase in demand placed on the heart may increase the risk of a heart attack."
People who are older and not exercising regularly need to pay special attention to the risks of a high-altitude visit, Cornwell said. A young, fit person might plunge into activity with only minor effects. This really becomes relevant, he said, for people who are in their middle age or elderly years who have high blood pressure, high cholesterol, or a history of heart attack or other cardiovascular issues.
With all this in mind, here's advice from Cornwell and Dow for anyone who wants to keep healthy and happy in the highlands.
Check before you go
If you have difficulty walking around your low-altitude home because of a weak heart, it's not going to be better in the high country, Cornwell said. So ask your health care practitioner, "Am I healthy enough to go? Are my risk factors under control? Am I on the right medications? Do I need to have some testing before I go?"
Your medications might need to be adjusted, Dow said, because some might suppress the body's response to lower oxygen. For example, beta blockers slow your heart, which normally would beat faster at altitude. However, Cornwell said this does not mean that a beta blocker should be stopped just because you want to go to the mountains, particularly if your doctor has started this medication for a good reason to protect your heart.
Take time to acclimate
This is crucial, both doctors said.
"If you have established conditions or you have risk factors, please consider one day to acclimatize," Cornwell said, "because that could have a very dramatic impact on your overall risk of something bad happening."
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Cornwell said it's common to see families fly from lower altitudes to Denver and then drive immediately to the ski resorts, some with summits around 13,000 feet. "They ski, they ice skate, they mountain climb – and someone ends up in a hospital with a heart issue."
Even relatively healthy people are at risk of fainting their first day at altitude, he said.
To give your body time to adapt, he suggests a "staged ascent." In the Colorado example, that could mean staying in Denver for a night before heading up to the resorts.
"We're talking 24 to 36, maybe 48 hours" from arrival at altitude before attempting strenuous activity, he said.
In the short term, a period of acclimation allows time for blood pressure to adjust. The body also makes a slight shift to the blood's acidity to help it retain oxygen better, Dow said. (Over many weeks or months, a person living at high altitude will actually develop more red blood cells – which deliver oxygen to body tissue – but vacationers wouldn't see that benefit, Cornwell said.)
Although a young, fit person may have lower cardiovascular risks, they should still take it easy the first day – if not for the sake of their health, then for the sake of their vacation, Dow said.
Mountain visitors who don't take time to adapt can experience acute mountain sickness, with symptoms such as fatigue, headache or nausea. Fitness trackers can give all kinds of helpful readings to help you know how well the body is adapting and to monitor altitude's effects, Cornwell said.
As a skier herself, Dow understands the allure of hitting the slopes on arrival. "If you've got that powder day, you don't want to miss it," she said. "But you may suffer for the next four days."
Drink this, not that
Anybody who has spent time in the mountains has heard how important it is to drink plenty of water. "Higher altitude environments tend to be more arid, so you just lose a lot more water through just through respiration," Dow said. That can exacerbate altitude-related symptoms.
But avoid alcohol, Dow said. Not only can it make symptoms of acute mountain sickness worse, but being tipsy can mask a condition known as high-altitude cerebral edema, a swelling of the brain. Symptoms include having trouble with words or tripping and staggering. And that is, she said, an emergency – "a 'get down now, get oxygen' emergency."
Have a plan
Getting away from it all might be the goal of a mountain visit, but you need a plan for the fact that you really are away from it all. Charming resort towns might lack cutting-edge medical facilities, and snowstorms can shut down major roads.
"You need to know where's the nearest hospital," Cornwell said. "You need to have an evacuation plan."
And if you take medications, you need to have extra on hand in case you end up staying longer than expected.
Watch out for one another
Talk with your travel companions before you go and agree to keep an eye on one another, Dow said. If someone is hiding away in their room or stumbling around, they might not be aware that they have a problem – and they might need medical attention.
So, agree that "if you see me tripping and falling, don't think it's just because I'm clumsy," Dow said. "And I won't think it's because you're clumsy. I'll think that we have to get you down (to a lower altitude) and take care of it."
The point of thinking about all of these issues isn't to scare anybody away from mountain fun, Cornwell said, even if they have conditions that require special attention. "What we're trying to do is help inform wise decision-making ahead of time to reduce the risk as much as possible."
American Heart Association News covers heart and brain health. Not all views expressed in this story reflect the official position of the American Heart Association. Copyright is owned or held by the American Heart Association, Inc., and all rights are reserved.