Atherosclerosis increases one's risk of clot formation because arterial plaque activates platelets which then adhere to the injured blood vessel wall, initiating platelet aggregation and the formation of thrombin. Simply preventing atherosclerosis through a heart-healthy lifestyle and/or drug therapy helps to prevent clotting. A heart-healthy lifestyle also helps to prevent clotting by preventing hypertension. Even borderline hypertension is associated with increased platelet aggregation and diminished fibrinolytic activity.

Smoking

If you need another reason to quit smoking, here it is. Smoking increases blood fibrinogen levels. Increased fibrinogen levels are associated with increased clotting risk. High fibrinogen levels increase platelet aggregation and fibrin deposition, and contribute to both clotting and plaque deposition.

Physical activity

Regular physical activity increases plasma volume. An increase in plasma volume means that the blood is more dilute, or "thinner," with a lower hematocrit (red cell count) and fibrinogen level and, consequently, a reduced risk of clotting. Several studies have shown that vigorous exercise also reduces platelet aggregability and enhances fibrinolytic activity. These effects may help to explain why active people are at lower risk for heart disease and stroke. Like most of the beneficial effects of exercise, these changes are short-lived, disappearing after two or three days. Regular, lifelong physical activity is the type of exercise that reduces clotting risk. A sedentary lifestyle, on the other hand, leads to increased clotting risk; blood thickens as plasma volume decreases. Sedentary people have stickier blood platelets, which in conjunction with higher levels of fibrinogen, are more likely to form blood clots.

An application of these observations is seen in the advice given to people prone to blood clots: Avoid sitting for extended periods, such as long airplane flights or car rides. Inactivity creates sluggish circulation in the arms and legs, and gives clots a better chance to form.

Stress

In the days of cave men and women, fighting and fleeing were often associated with bleeding, so it makes sense that enhanced clotting speed is part of the fight-or-flight response, even though clotting is not so useful nowadays. Prolonged mental stress impairs fibrinolysis by decreasing the activity of an enzyme called tissue plasminogen activator (tPA), which helps break down fibrinogen.

Heart-healthy diet: Reducing atherogenesis and thrombogenesis

People with high serum cholesterol levels exhibit disturbances in coagulation, fibrinolysis and platelet behavior. Lowering blood lipid levels by diet or drug therapy seems to reverse these disturbances, and may be one mechanism whereby a heart-healthy lifestyle reduces heart disease risk, in addition to its effects on atherogenesis. An interesting study from Denmark found that volunteers who stuck to a low-fat, high-fiber diet showed increased fibrinolytic activity and, thus, a reduced risk of blood clot formation.

A moderate alcohol intake (one to two drinks per day) has been associated with a reduced heart disease risk. This risk reduction may be due in part to the increase in fibrinolysis observed in moderate drinkers.

REFERENCES

Meade, T. W. Haemostatic function and arterial disease. British Medical Bulletin 50: 755-775, 1994.

Ridker, P.M., D.E. Vaughan, M. J. Stampfer, et al. Association of moderate alcohol consumption and plasma concentration of endogenous tissue-type plasminogen activator. Journal of the American Medical Association 272: 929-933, 1994.

Szymanski, L.M., R. R. Pate, & J. L. Durstine. Effects of maximal exercise and venous occlusion on fibrinolytic activity in physically active and inactive men. Journal of Applied Physiology 77: 2305-2310, 1994