Why you shouldn't drink before dozing off on long-haul plane flights

If you enjoy having a glass of wine or a cocktail before dozing off during long airplane flights, you might want to reconsider it, a new study suggests.

A series of lab experiments discovered that when people fall asleep after consuming alcohol at the low air pressures typically experienced during airline flights, blood oxygen drops to worrisome levels and heart rates increase even in those who are healthy and young, according to the report published Monday in the journal Thorax.

The new research should give airline passengers who like to drink while flying pause, said study co-author Dr. 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.

Even when we don’t drink, commercial flying can be taxing for the body. Dry cabin air can cause dehydration and being immobile in cramped seats for hours can sometimes trigger blood clots in the legs. At cruising altitude, cabin pressure is set to what would be experienced between 6,000 to 8,000 feet above sea level, which can contribute to lower oxygen saturation in the blood. As air pressure decreases the amount of oxygen a person takes in with each breath also declines, according to the National Institutes of Health.

The German scientists expected that alcohol consumption at low air pressure would have an effect on people, but “we were surprised to see that the effect was so strong,” Elmenhorst said, urging flyers: “Please don’t drink alcohol while being on an airplane.”

While young, healthy people most likely won’t experience any serious harm to their hearts from drinking while flying, in others “the decreased oxygen saturation together with the increase in heart rate could exacerbate pre-existing medical conditions,” Elmenhorst said.

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

For the study, 48 healthy adults between the ages of 18 and 40 were randomly assigned to one of two groups: Half would go to a sleep lab that had air pressure at sea level, while the other half would sleep in an altitude chamber that mimicked the air pressure found on planes traveling at cruising altitude.

Twelve people in each group slept for four hours after having consumed the equivalent of two cans of beer or two glasses of wine, while the other 12 slept after consuming no alcohol. After a break of two days, the procedure was reversed, so that those who had consumed alcohol before sleeping now slept with no alcohol on board and vice versa.

People who drank before falling asleep in the altitude chamber on average had their blood oxygen saturation drop to 85%, while their heart rates rose to compensate for the lower oxygen levels to an average of nearly 88 beats per minute.

That’s compared to a blood oxygen saturation drop to 95% and a heart rate rise to 77 beats per minute in those who consumed alcohol at sea level before falling asleep.

An oxygen saturation of 95% to 100% is normal for healthy adults and children, according to the Centers for Disease Control and Prevention.

Experts say that a drop to below 90% in oxygen saturation is worrisome.

Under 90% would be concerning, said Dr. Deepak Bhatt, director of the Mount Sinai Fuster Heart Hospital in New York.

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

In someone with heart disease, the combination of the effects described in the study could trigger bad cardiovascular outcomes, like a heart attack, a stroke or blood clots forming, Bhatt said.

The new study is “important given the number of people who fly internationally, said Mariann Piano, a professor of nursing and a researcher who has studied the impact of alcohol on heart health at the Vanderbilt University Medical Center in Nashville. Those longer flights could put people who drink at greater risk.

“What I found concerning was the drop in oxygen saturation,” Piano said. “It was approaching a very abnormal level that could compromise the delivery of oxygen to the tissues of the body.”

Especially concerning would be the impact on people with chronic obstructive pulmonary disease, Piano said. “They have lower baseline oxygen saturation levels,” she said.

While healthy young people are probably not at serious risk, this study suggests people with underlying cardiorespiratory conditions should “steer away from alcohol when flying,” said Dr. Prashant Vaishnava, a cardiologist and an assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons in New York.

For people without health issues who would really like a beer or a glass of wine on a flight, “they should be conservative and limit themselves to probably no more than one drink,” Vaishnava said.

This article was originally published on NBCNews.com