Information about the risks of so-called "economy class syndrome" is to be distributed with tickets by British Airways. The public have become more aware of potentially-fatal deep vein thrombosis following a number of deaths among long-haul airline passengers.
Now British Airways is sending out leaflets containing health tips on preventing the illness to anyone booking a long flight.
It is also distributing leaflets and posters to GP surgeries.
A British House of Lords report recommended that airlines make more effort to make customers aware of the potential hazards. But the airlines insist that the recent spate of reports of deaths is unconnected with its latest initiative.
A spokesman said: "It is about well-being in the air, and we have always talked about well-being in the air." Sitting still for long periods may increase the chances of developing the blood clot which can cause problems.
The clots are dangerous when they block blood vessels in the leg, or worse, in the lungs.
Passengers are advised to drink plenty of water, and take exercise such as going for a stroll up and down the aisle every now and then during the flight.
The condition is referred to "traveller's thrombosis" in the leaflets.
"Economy-class syndrome" is a misnomer, because the condition is not necessarily dependent on the smaller legroom seats in that section.
The illness is more likely to arise in the elderly and overweight, and drinking alcohol instead of water can cause dehydration which increases the risk.
However, the condition could arise in any patient who is sitting still for a prolonged period. Mr John Scurr, a consultant vascular surgeon, said: "Blood clots in the leg can occur in all travellers. The longer you sit down, the more likely you are to get a clot - so it's not restricted just to air passengers."
The relatives of one passenger who died in November from deep vein thrombosis are believed to be considering legal action against the airline which carried him shortly before he fell ill.
Father-of-four Thomas Lamb, 68, died shortly after arriving at Heathrow from Australia.
Business class passenger Susan Mavir-Ross, from north Wales collapsed and died on a Virgin flight from San Francisco earlier this year.