You’ve likely read plenty of stories about what you should and shouldn’t be eating and drinking to feel your best on a flight. Stories that recommend avoiding the tap water on planes as it’s likely riddled with germs (this goes for the ice, too). And how you should skip gas-inducing foods at 35,000 feet as the air pressure changes can make an already uncomfortable situation worse. Then, there’s why you should never order pasta on board — less for safety and more because it’s probably overcooked. But now, scientists are giving us one more to add to the list: You should avoid alcohol, especially if you plan to nap on your flight. 

In early June, a group of German researchers published a study on the “effects of moderate alcohol consumption” on passengers’ sleep, oxygen saturation, and heart rate on long-haul flights in the journal Thorax. Its findings will have you second-guessing that tipple. 

To find out exactly what alcohol does to us on planes, the researchers asked 48 adults to sleep in a specially designed space that recreates the atmospheric pressure of a plane, as well as creates a similar overall environment. Participants were asked to sleep for four hours on two occasions — once after drinking alcohol (the equivalent of two glasses of wine) and once without it. The team found that even a moderate amount of alcohol had significant effects. 

“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,” the researchers noted in their findings. And it’s not just your cardiac system that’s impacted. As the research added, the participants’ time in REM sleep was also greatly reduced, showing that any sleep they did get, didn’t do much for them. 

The researchers aren’t the only ones who caution against having a drink in the air, either. 

“Drinking on airplanes is not usually a good idea. It sets the stage for poor sleep and cardiac events by lowering oxygen saturation and increasing heart rate,” Lindsay Malone, a nutritionist and professor at the School of Medicine at Case Western Reserve University, shared with Travel + Leisure. “And keep in mind that your health usually takes a hit with travel anyway — extended times sitting, more eating out, less time to exercise, poor sleep due to time changes, dehydration, and more.” 

Dr. Mary Branch, a board-certified cardiologist, agreed, telling T+L that if you have medical issues, including severe obstructive sleep apnea, COPD, pulmonary fibrosis, sarcoidosis, or heart failure, you should avoid alcohol on planes. But, she added, if you’re generally healthy, you don’t need to say “no” forever. 

“Based on this data, I would not restrict everyone from drinking alcohol,” said Branch. She added, “If you’re healthy, try to limit your alcohol intake on the plane.” 

Malone’s suggestion is also an easy one to take: “Save the drinks for your destination.” On the flight, Malone says it’s a good idea to go for a nonalcoholic drink, like a low-sugar mocktail or even a nonalcoholic beer if you have the option. “Better yet, prepare for the ideal nap on your flight by bringing an eye mask, blanket, and neck pillow. Listen to a deep rest meditation or settle into a good book before dozing off. You’ll be well-rested and ready to tackle whatever your trip brings.”