Spending time at high altitudes may raise your blood pressure, according to a growing body of evidence, and these spikes may be particularly dangerous for people with existing heart disease.
In one study, researchers found that blood pressure steadily increased as climbers ascended Mount Everest, the highest mountain on Earth. What's more, telmisartan, a drug widely used to treat high blood pressure, no longer worked once climbers reached a certain altitude. The findings appeared in an November 2014 issue of the European Heart Journal.
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Forty-seven volunteers wore blood pressure monitors that took round-the-clock readings as they climbed to Mount Everest base camp, which is at an altitude 17,700 feet. They showed an increase of 14 millimeters of mercury per deciliter of blood in systolic blood pressure (the upper number) and 10 millimeters of mercury in diastolic blood pressure (lower number) over a 24-hour period of monitoring.
Read more: Heart Rate and High Altitudes
How High Is Too High?
High blood pressure, known as hypertension, is considered to be 130 millimeters of mercury or higher for the systolic blood pressure or 80 and higher for diastolic pressure, according to the American Heart Association. Often called the "silent killer" because there are sometimes no obvious symptoms until it is too late, high blood pressure is a major risk factor for heart attacks and strokes.
High altitude is defined as 8,000 to 12,000 feet above sea level, according to the Cleveland Clinic. Very high altitude is defined as 12,000 to 18,000 feet, and altitudes above 18,000 feet are considered "extremely high." For context, New York City has an altitude of 33 feet; Denver is at 5,000 feet; and Arizona's Grand Canyon is 6,600 feet above sea level.
Several groups of medical experts have issued recommendations on the risks of higher altitudes for people with existing heart conditions. They report that altitudes that are 8,200 feet above sea level may increase blood pressure and heart rate and that people with preexisting heart disease may be even more vulnerable in the face of these changes. Their recommendations were published in the May 2018 issue of the European Heart Journal.
"Both the sympathetic nervous system and renin-angiotensin system can be activated at high altitudes," says George Bakris, MD, a professor of medicine and director of the American Heart Association Comprehensive Hypertension Center at the University of Chicago Medicine.
It's a double whammy, he explains. The sympathetic nervous system can stimulate the release of the stress hormone adrenaline, which speeds up the heart rate and blood pressure levels. The renin-angiotensin system stimulates production of angiotensin II, which constricts blood vessels, causing them to narrow.
"Flying to Denver likely won't cause this, but spending time above 8,000 feet may cause these changes in blood pressure," Dr. Bakris says.
Blood pressure changes aren't the only risk of spending time at higher altitudes. So-called mountain or altitude sickness is marked by headache, nausea, vomiting and lightheadedness. It occurs because your body doesn't have enough time to adapt to the lower air pressure and lower oxygen levels in the air at high altitudes, the Cleveland Clinic explains. Sometimes, altitude sickness can cause you to become short of breath even at rest and make it difficult to walk.
If you are negatively affected by high altitude or changes in altitude, taking precautions can keep any symptoms at bay and stop them from getting worse, according to the Centers for Disease Control and Prevention (CDC) and the Cleveland Clinic.
If you will be spending time at higher altitudes, they recommend that you:
- Drink at least 3 to 4 quarts of water a day.
- Don't smoke, drink alcohol or take any depressant drugs.
- Ask your doctor about a medication called Diamox (acetazolamide) to help you acclimate to the higher ground.
- Know the early signs and symptoms of altitude sickness and get help.
- Ascend gradually.
- Continue drinking coffee if it is part of your day-to-day routine.
- Exercise only mildly for the first 48 hours.
The good news is that mild symptoms of altitude sickness improve once you return to a lower ground, the Cleveland Clinic states.
- European Heart Journal:” Changes in 24 h Ambulatory Blood Pressure and Effects of Angiotensin II Receptor Blockade During Acute and Prolonged High-Altitude Exposure: a Randomized Clinical Trial”
- American Heart Association:” What is High Blood Pressure?”
- Cleveland Clinic: "Altitude Sickness”
- European Heart Journal: “Clinical Recommendations for High Altitude Exposure of Individuals with Pre-existing Cardiovascular Conditions: A joint Statement by the European Society of Cardiology, the Council on Hypertension of the European Society of Cardiology, the European Society of Hypertension, the International Society of Mountain Medicine, the Italian Society of Hypertension and the Italian Society of Mountain Medicine”
- George Bakris, MD, professor of medicine, director, American Heart Association Comprehensive Hypertension Center, University of Chicago Medicine
- CDC: "High-Altitude Travel and Altitude Illness”
- Cleveland Clinic: "Mountain Vacation? 5 Tips to Cope With Your Altitude Sickness"
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.