The next time you board a long flight and decide to enjoy an alcoholic drink before taking a nap, you might want to avoid the temptation.
A new study, published in the medical journal Thorax on Monday, found that when people fell asleep after drinking alcohol in a low air pressure environment similar to that on airplanes, their blood oxygen decreased and their heart rates increased. Researchers observed this trend even in people who were young and healthy.
“Even in young and healthy individuals, the combination of alcohol intake with sleeping under hypobaric conditions poses a considerable strain on the cardiac system and might lead to exacerbation of symptoms in patients with cardiac or pulmonary diseases,” researchers said in the study.
“Higher doses of alcohol could amplify these observed effects, potentially escalating the risk of health complications and medical emergencies during flight, especially among older individuals and those with pre-existing medical conditions,” researchers continued. “Our findings strongly suggest that the inflight consumption of alcoholic beverages should be restricted.”
To conduct the study, researchers split 48 healthy adults between the ages of 18 and 40 into two groups: the first went to a sleep lab with sea-level air pressure, and the second went to an altitude chamber with air pressure similar to that on planes traveling at cruising altitude, NBC News reported. In each group, 12 participants slept for four hours after consuming alcohol, equivalent to two cans of beer or two glasses of wine. The other 12 in each group slept without consuming alcohol.
The experiment had a break of two days, and then the participants’ roles were reversed—the participants who had consumed alcohol before sleeping then slept without consuming alcohol, and vice versa.
The participants who drank alcohol before sleeping in the altitude chamber had their blood oxygen saturation decrease to 85%, on average, the study found. Their heart rates increased to an average of about 88 beats per minute, likely to compensate for the lower oxygen levels.
In comparison, those who drank alcohol at sea level before sleeping had their blood oxygen saturation dip to 95% and their heart rates increase to 77 beats per minute, the study found.
Read More: Yet Another Study Suggests Drinking Isn’t Good for Your Health
Healthy individuals typically have an oxygen saturation between 95% to 100%, according to the Centers for Disease Control and Prevention. Experts say that an oxygen saturation below 90% is cause for concern.
Researchers told NBC News that they hoped people who like to drink on flights reconsider next time, given the results of this study.
“We were surprised to see that the effect was so strong,” Dr. Eva-Maria Elmenhorst, one of the study’s authors and deputy of the department of sleep and human factors research at the Institute of Aerospace Medicine at the German Aerospace Center in Cologne, Germany, told NBC News. “Please don’t drink alcohol while being on an airplane.”
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