New research out of Germany has experts urging passengers to think twice about drinking alcohol before snoozing on their next flight. The study has revealed that even a small amount of alcohol can put a lot of stress on your heart. We know, it’s a bummer.

Study co-author Dr Eva-Maria Elmenhorst of the Institute of Aerospace Medicine at the German Aerospace Center in Cologne found that blood oxygen levels dipped significantly in those who consumed alcohol when flying compared to those who didn’t. 

The study, published in the medical journal Thorax, also found that the effects of consuming alcohol at sea level versus in-flight were less damaging for those planted firmly on the ground.

A series of lab tests revealed that when you fall asleep after consuming alcohol – at any altitude – your blood oxygen levels decrease. When a plane reaches cruising altitude, the cabin pressure is set to around 6,000 feet above sea level. When you fall asleep at cruising altitude, blood oxygen levels dip much further than when at sea level. 

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Why is this important? Well, when your blood oxygen level drops, your heart rate increases to compensate and to get more oxygen flowing to your vital organs. The more strain you put on the heart, the higher the risk of negative cardiovascular events like a stroke, a heart attack, or the forming of blood clots.

For a healthy adult, blood oxygen levels should sit around the 95-100 percent mark. Researchers found that falling asleep after as little as one or two standard drinks at cruising altitude caused blood oxygen saturation to drop to 85 percent while heart rates rose (on average) to 88 beats per minute.

In the group who consumed two standard drinks at sea level before sleeping, oxygen levels only dropped to around 95 percent, with a heart rate rise to 77 beats per minute.

This isn’t to say you cannot drink at all on a plane (we’re not monsters) but if you’re a healthy adult, go ahead and treat yourself. In moderation, of course.

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