Drinking and napping on long-haul flights may not be good for the heart, even among the young and healthy, finds a study on Tuesday.

Together, this can lower the amount of oxygen in the blood (SpO2) and increase the heart rate for a protracted period, revealed the study, published online in the respiratory journal Thorax.

This may increase with higher alcohol consumption, particularly among the elderly with pre-existing medical conditions.

“Atmospheric pressure decreases exponentially with altitude, causing a drop in blood oxygen saturation level to around 90 percent (73 hPa) in healthy passengers at cruising altitude,” said researchers from the German Aerospace Center in Cologne, Germany.

A further drop in SpO2 is defined as hypobaric hypoxia — or low blood oxygen level at higher altitude.

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“Alcohol relaxes blood vessel walls, increasing the heart rate during sleep, an effect similar to that of hypobaric hypoxia,” the researchers said, suggesting to “consider limiting alcohol on long haul flights”.

The study randomly allocated 48 people to two groups — half were assigned to a sleep lab under normal ambient air pressure conditions (sea level) and half to an altitude chamber that mimicked cabin pressure at cruising altitude (2,438 m above sea level).

Twelve in each group slept for 4 hours, having drunk alcohol and not having drunk.

“The results indicate that, 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,” said the researchers.