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A link between air travel and a higher risk of deep-vein thrombosis (DVT) is widely suspected, but the causes are uncertain. Aviation Health (AH), an independent body dealing with aviation issues, suggests precautionary measures. Unless contraindicated, a low-dose aspirin (100-150mg) taken the day before a flight, on the day and for two or three days after can reduce the risk of pulmonary embolism by up to 60 percent. Studies at Dokkyo University, Japan, meanwhile, found that a natural protein in fermented soya beans has an anti-thrombotic effect similar to that of the anti-coagulant drug heparin

Stay hydrated

Relative humidity in the cabin can be anything from 2-23 per cent, well below the 30-65 per cent comfort zone; and the fewer passengers on board, the drier the atmosphere. “Dry air hampers the respiratory system’s defences, so increasing susceptibility to infection,” says Professor Ron Eccles of the Common Cold Centre. He recommends sipping water before and during the flight, to keep sinuses moist and boost their effectiveness at flushing out viruses.

And avoid carbonated drinks, says Farrol Kahn, director of AH: “At altitude, gases in the digestive system can expand by a third, causing abdominal pain.” One non-fizzy alcoholic drink before takeoff is fine (to soothe pre-flight nerves), but avoid it on board: alcohol dehydrates and further reduces oxygen supplies to the brain.

Don’t be calm

Nervous about takeoff? Hypnotherapist Ursula James says that, on the eve of a flight, you should try to visualise yourself relaxed, walking on to the plane, sitting through the flight, then landing, cool and collected. If pre-flight anxiety surfaces, it helps to imagine a time when you felt eager, but not fearful, anticipation.

“Recalling an exciting rather than a calm event works with the physiology of stress,”

she says. “Anxiety and excitement are identical in physical terms — short breath, butterflies and so on — so changing the psychological overlay from one to the other is easier than trying to force an opposite state such as calm.’’

Shake a leg

Longer check-in times mean you’re likely to be waiting in terminals for many hours, most of them seated. Kahn advises taking a brisk walk at every opportunity, to bolster circulation. Pre-flight exercise will relax you, and also reduce the likelihood of in-flight aches and stiffness. On board, do the anti-DVT exercises that many airlines provide these days. Walk up and down the aisles when you can, too. “Aim for around 15 minutes’ movement every hour,” Kahn says.

Eat light

After a meal, the body diverts oxygenated blood to the gut to help fuel digestion. With up to 25 per cent reduced oxygen on board, eating heavily can strain the body and the digestive system, which will “summon’’ oxygen from anywhere it can — the brain included — leaving you vulnerable to fainting should you then leave your seat. Instead, snack — lightly. Salads and fruit are good, because they are water-rich, so contribute to hydration, and contain mostly carbohydrates, which are comfortably digested. Avoid gas-producing food such as legumes or brassicas.

Keep your hands clean

A 2002 study at the University of California found that, of 1,100 passengers flying from San Francisco to Denver, one-fifth reported cold symptoms within a week of arrival. “Every surface of the plane is covered in bacteria and viruses, not just those of your fellow

passengers, but those of other passengers who’ve flown on that plane in the past 24 hours,’’ says the UK’s Common Cold Centre’s Ron Eccles. He recommends regular use of alcohol-based hand wipes to protect against two of the more common means of disease transmission — into the eye or nose via infections gathered on fingertips.