What risk factor is associated with Budd-Chiari syndrome?

Budd-Chiari syndrome is primarily associated with the obstruction of blood flow from the liver, which can be caused by various conditions that increase the risk of thrombosis. Smoking is a recognized risk factor for the development of venous thromboembolism (VTE), which can lead to conditions such as Budd-Chiari syndrome. The substances in tobacco smoke can lead to changes in blood coagulation and vascular health, thus heightening the risk for thrombotic events.

The other options do not have a direct correlation with the risk of Budd-Chiari syndrome. Increased physical activity typically reduces the risk of thrombosis by promoting healthy circulation, while a low protein diet is not directly linked to this condition. Frequent travel has been associated with venous clots, but smoking has a more established and potent connection to the thrombotic processes that can lead to Budd-Chiari syndrome. This makes smoking the correct option among the given choices.