Deep vein thrombosis (DVT,) a largely preventable circulatory problem associated with inactivity, is getting some overdue attention. DVT kills 200,000 people each year, more than breast cancer, AIDS and highway fatalities combined, yet relatively few people know what it is and fewer still know its symptoms. It is the largest single cause of in-hospital deaths. DVT means blood clots, usually forming deep in the leg veins. When the clot, or part of the clot, breaks free, it can lodge in the lungs forming a usually fatal pulmonary embolism.

DVT is sometimes called "economy class syndrome" because the inactivity on extended flights can lead to it. The hospitals around Heathrow Airport in London estimate they lose one patient a month to DVT exacerbated by long haul flights.

Though associated with the more cramped economy class, DVT can affect anyone on extended or frequent flights, including first class passengers such as former Vice President Dan Quayle, who was treated for DVT in 1994.

DVT has recently been brought to the national spotlight following the death of NBC reporter David Bloom. Mr. Bloom, 39, died after an extended tour in a cramped military vehicle reporting the war in Iraq. His widow, Melanie, wants to educate the public at large of this growing threat.

Bloom had the classic symptoms of DVT, apparent in only half the cases. The other fifty per cent show no symptoms. He complained of pain and cramping in his lower legs, behind the knees. Other symptoms include tenderness and a bluish tinge around the affected area.

Sometimes the throbbing can be mistaken as a pulled muscle and symptoms can appear days or even weeks after the flight or other immobility. The doctors Bloom consulted suspected DVT and advised immediate attention, but he put off taking their advice until it was too late, dying of a pulmonary embolism.

While a number of factors contribute to DVT, including genetic predisposition, cancer treatments, pregnancy and joint surgery, you can increase your odds of not developing DVT significantly by three simple strategies:

1) Do not smoke. Smoking is the single greatest threat to circulatory health and, no matter how cool Hollywood makes it look, lighting up is just plain stupid.

2) Keep moving. Get up from that computer and walk, dance, swim, ride a bike, and always take the stairs. Put forth a little effort. Keep your blood moving and your veins clearer.

3) Keep your weight down. Obesity is a contributing factor for so many illnesses and early deaths like this one can't be emphasized enough. Exercise and eat a diet low in fat and rich in vegetables, whole grains, lean proteins and fruits.

If you have the least suspicion that you may have DVT, get yourself to the emergency room. Time is critical and there a very few second chances.

Brenda Berstler is the founder of the Walking Example Group (WE-GO) a non-profit organization encouraging walking and walkable communities. Visit their website at www.we-go.org.