Deep vein thrombosis (DVT) is caused when a blood clot forms in veins where blood flow is sluggish or has been disturbed, hence the increased risk with immobility caused by long distance travel. The potentially lethal risk with DVT is that a blood clot will break away from its site of formation, and travel to the lung arteries, plugging them and causing a pulmonary embolism.
When the link between long-haul air travel and the condition was first established the WHO recommended that people should be sure to move about regularly when travelling.
But Victor Ferrari, CEO of Horphag Research, the maker of supplement Pycnogenol from French maritime pine bark that has been researched for DVT risk reduction prevention, said he is not convinced that airlines' diagrams of how to do "gymnastics with the feet", or a few extra inches of leg-room, are not enough to fully address the problem.
The UK's department of health estimates that DVT occurs in one in every 2000 people, but according to Dr Gianni Belcaro from the Chieti-Pescara University in Italy., who has led in studies on Pycnogenol and DVT, four to six per cent of air travellers develop blood clots - which may or may not develop into the life-threatening condition.
Dr Belcaro told NutraIngredients.com that research on three or four other natural products is promising.
A supplement called Flite Tabs that contains Pycnogenol and nattokinase from fermented soybeans has also been researched for superficial thrombosis.
UK-based Provexis also revealed that it is in discussions with airlines over the use of its tomato-derived Fruitflow technology, seen to inhibit blood platelet aggregation, to reduce DVT risk.
But despite the potential, there are barriers to marketing natural products to reduce the risk of DVT, which are proving hard to overcome.
While it might seem to make sense to position the substances in the same location as the DVT threat occurs - on airplanes - according to Ferrari interest from airlines' marketing departments tends to meet with opposition from their legal colleagues, who fear liability.
"It is funny how the airlines are dealing with the issue," he said.
Ferrari said that his discussions with airlines are on-going, but he is not able to disclose details at this time.
Dr Belcaro put the fact that an airline has yet to embrace a natural product down to their priorities at the moment, which lie with safety in the skies and making money.
"They have other problems. This is a cost-cutting period, they are not investing in anything," he said.
In the meantime, Horphag co-developed a supplement called Zinopin, together with a company set up for the purpose called Pynogin. The formula, containing high doses of the pine bark extract Pycnogenol and standardized ginger extract, was launched in the UK in 2004 and is endorsed by leading vascular surgeon Dr John Scurr, an expert on travel-related DVT.
However despite the research (and Dr Belcaro's conviction that for Pycnogenol the research "is strong enough for it to be marketed for this use"), regulatory restrictions mean the product cannot make bold DVT risk-reduction claims on packaging or marketing materials.
The only real route presently available is to communicate the research, particularly to the medical community so that doctors can make recommendations to their patients.
The best scenario, he thinks, would be if a medical doctor from an airline were to take the responsibility to validate the different approaches - be it Pycnogenol, Warfarin, aspirin, or some other substance.
But airlines do not tend to have dedicated medical authorities, so it is thrown back at the passenger to be their own doctor.
From the perspective of a consumer wishing to reduce their risk of DVT, they may be more likely to take a pill prior to travel than they are to have an injection with a drug such as Warfarin.
Ferrari said that awareness of the link between air travel and DVT remains low, especially in the US and continental Europe. Part of the problem is that although the clot forms during travel, the thrombotic events only take place two days later so the connection is not always made between the two events.
Dr Belcaro concurred. People are seduced by cheap seats, and there is a widespread notion that if you don't fly, it's not a real holiday.
This means that people who are at a high-risk of DVT - such people with diabetes, age-related health conditions, or someone with a broken leg - may board a plane nonetheless.
His prescription: "If you're not fit to fly, wait a few months."