• German researchers have recommended avoiding alcohol on flights due to the increased health risks identified in a new study.
• The combination of alcohol consumption, sleep and the low oxygen concentration at high altitudes was found to reduce blood oxygen saturation, increase heart rate and slash quality of sleep.
• The effects were identified in young and healthy study participants, while risks are exacerbated for older people and those with pre-existing medical conditions.

A popular pastime on long-haul flights — drinking alcohol before dozing off to sleep — may present health risks even to young and healthy passengers, according to a new study.

The combination of alcohol consumption, sleep and the low oxygen concentration at high altitudes was found to challenge the cardiovascular system and extend the duration of hypoxaemia, or low levels of oxygen in the blood.

The researchers at the German Aerospace Center's Institute of Aerospace Medicine and Aachen University also said the habit reduced sleep quality and recommended that airlines restrict inflight consumption of alcoholic drinks.

Study co-author Eva-Maria Elmenhorst told NBC News that the team was "surprised to see that the effect was so strong" and recommended avoiding alcohol while flying.

Inflight sleep already exacerbates the fall in blood oxygen saturation caused by the reduced atmospheric pressure in aircraft cabins, the study states.

Under the added effect of alcohol consumption, lab tests showed that participants' blood oxygen saturation decreased further, their heart rate increased and deep sleep was reduced.

Even "young and healthy participants" suffered from "clinically relevant" desaturations and heart rate accelerations during sleep, the study found.

"Higher doses of alcohol could amplify these observed effects, potentially escalating the risk of health complications and medical emergencies during flight, especially among older individuals and those with pre-existing medical conditions," it added.