Obese people taking holidays at high altitude face much greater risks of falling ill, say researchers.
Obesity may be the root cause
Researchers at the University of Texas Southwestern found that acute mountain sickness was more likely to develop in obsese patients.
The condition is normally linked to rapid ascent from low level to 8,000 feet or more.
Symptoms include headache, nausea, vomiting and fatigue.
Scientists suggest that impaired breathing during sleep may be to blame.
They warn that obese people should take their time getting to altitude to minimise the risk of problems.
Dr Tony Babb, the study's senior author, said: "We recommend that when travelling to high altitudes obese individuals, even those without a history of acute mountain sickness, take precautions to ensure a slow, gradual ascent.
"In addition, these individuals should consider taking the prescription medication acetazolamide, which has been effective in preventing altitude sickness in susceptible travellers."
The boom in travel to exotic locations means that it is not just those used to at least some physical activity, such as mountaineers, skiers and trekkers, who can be transported to higher altitudes.
The study looked at a small number of men - nine obese and 10 non-obese, who spent 24 hours in a decompression chamber.
The pressure was held constant at the equivalent of 12,000 feet altitude.
The majority of the obese participants - 78% developed symptoms of acute mountain sickness.
Two in five of the other participants fell ill.
Dr Babb added: "Symptoms of altitude sickness were more severe in the obese study participants, which indicates the occurrence of acute mountain sickness may be closely related to increased body weight."
The study was published in the journal Annals of Internal Medicine.