Study details and key findings

For the study, researchers randomly assigned 48 healthy adults between the ages of 18 and 40 to sleep in either a sleep lab with sea-level air pressure or an altitude chamber with air pressure like a plane at cruising altitude.

In each group, 12 participants slept for four hours after drinking the equivalent of two cans of beer or two glasses of wine. The other 12 participants slept without drinking any alcohol. After a two-day break, the participants switched, with the non-alcohol group now drinking alcohol and vice versa.

Overall, the researchers found that people who drank alcohol before sleeping in the altitude chamber had their blood oxygen saturation decrease to an average of 85% and their heart rates increase to an average of almost 88 beats per minute.

In comparison, participants who drank alcohol before sleeping in the sleep lab had their blood oxygen saturation decrease to 95% and their heart rate increase to 77 beats per minute. According to CDC, an oxygen saturation of 95% to 100% is normal for healthy individuals. However, experts say that dropping below 90% is concerning.

"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," the researchers wrote.

The researchers also analyzed participants' quality of sleep and found that those who drank alcohol had worse sleep. Participants who drank alcohol had shorter REM sleep, the stage of sleep that may help with memory consolidation and brain recuperation.

Commentary

According to Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health, the study is small, but it provides researchers with a starting point to investigate the potential relationship between sleep, flight, and alcohol.

Separately, Mariann Piano, a professor of nursing at Vanderbilt University Medical Center who has studied the effects of alcohol on heart health, said the study is "important given the number of people who fly internationally." People who drink on longer flights could have a greater risk.

Eva-Maria Elmenhorst, deputy of the department of sleep and human factors research at the Institute of Aerospace Medicine at the German Aerospace Center in Cologne, Germany, and one of the study's authors, said the researchers expected alcohol consumption at low air pressure would affect people, but "we were surprised to see that effect was so strong."

Although young, healthy people are unlikely to experience serious harm to their hearts if they drink while flying, "the decreased oxygen saturation together with the increase in heart rate could exacerbate pre-existing medical conditions" in others, Elmenhorst said.

"The oxygen saturation dropped to quite low levels during sleep," she added. "This is why I would recommend to avoid drinking alcohol even when someone is healthy."

Other health experts agreed with Elmenhorst. According to Deepak Bhatt, director of the Mount Sinai Fuster Heart Hospital, the effects described in the study could trigger severe cardiovascular outcomes, including a heart attack, stroke, or blood clots, in someone with heart disease.

"For years I've been telling patients not to drink on flights," Bhatt said. "This study makes me more confident in that advice."

Prashant Vaishnava, a cardiologist and an assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, said that while healthy young people are probably not at serious risk, people with underlying cardiorespiratory conditions should "steer away from alcohol when flying."

Vaishnava also recommended that people without health issues "be conservative and limit themselves to probably no more than one drink" while flying. (Carroll, NBC News, 6/3; Lee, TIME, 6/3; Holcombe, CNN, 6/4)

Compared to people who never drink alcohol, people who drink low or moderate amounts didn't see any reduction in risk of death from any cause, according to a study published in JAMA Network Open, findings that contradict previous studies that suggested moderate drinking could come with some health benefits.