For some, a glass of champagne when boarding a plane or a red wine with dinner is one of the silver linings of a flight, especially a long one.

However, if you plan to sleep on the plane you may want to reconsider accepting an alcoholic drink according to a study published on Monday in the journal Thorax.

Falling asleep after alcohol in a low-air pressure environment (such as an aeroplane cabin) can put “considerable strain” on your cardiac system and could increase the risk of health complications, stated the study.

Researchers were surprised to find blood oxygen levels dropped and heart rates increased, even in young, healthy people, but concluded the risk of this causing health issues was higher for those with pre-existing medical conditions or who are older.

Dr Eva-Maria Elmenhorst, one of the researchers from the Department of Sleep and Human Factors Research at the German Aerospace Center, told NBC News the results were more significant than expected.

“We were surprised to see that the effect was so strong,” Elmenhorst said before advising travellers to avoid drinking alcohol on aeroplanes or at least restricting how much they consume.

What happens when you drink and then sleep on a plane?

The study split 48 adults aged 18 to 40 into two groups; one group went to a sleep lab set to air pressure you would find at sea level and the other group were sent to sleep in an altitude chamber set to ‘cruising altitude’ on a plane.

In each group, 12 people were given two standard alcoholic drinks before sleeping, and two days later the study was repeated with the drinking and non-drinking groups swapped.

Those who drank before sleeping and stayed at sea level had their heart rate increase to 77 beats per minute and their blood oxygen saturation drop to 95 per cent.

On average, those at cruising altitude reported a heart rate of 88 bpm and blood oxygen saturation of 85 per cent.

Researchers noted the study’s sample size was small and only explored the effects of alcohol when people slept for four hours, not more or less, but claimed the findings aligned with existing studies.

The typical blood oxygen saturation is between 95 and 100 per cent, meaning those who drank then slept at altitude had their levels drop a worrying amount, one expert told NBC News.

“For years I’ve been telling patients not to drink on flights,” said the director of New York’s Mount Sinai Fuster Heart Hospital, Dr Deepak Bhatt.

Bhatt told NBC News any blood oxygen level under 90 per cent was concerning and the study’s findings made him confident his advice to patients was worthwhile.