A number of medical conditions require the use of blood thinning agents -- also known as anticoagulant medications -- to prevent the formation of blood clots, which can cause a stroke and heart attack. A variety of natural substances also have blood-thinning effects, including some common foods and nutritional supplements.
The authors of a March 2001 summary article published in "JAMA Internal Medicine" report that garlic has been found in some studies to inhibit platelet aggregation -- one of the initial steps in blood clot formation. Other studies, however, have found that garlic does not have blood-thinning effects when taken alone at daily recommended doses.
The authors of a May 2013 article published in "Critical Reviews in Food Science and Nutrition" examined all of the published medical studies to date evaluating medical uses of garlic. They concluded that there is insufficient evidence to determine whether garlic may be useful for the prevention of blood clots. However, it may have additive blood-thinning effects when taken in large quantities or with anticoagulant medications. Further research on garlic's blood thinning properties is needed.
Fish and Fish Oil
Fish contains the omega-3 fatty acids EPA and DHA, which have been shown to have blood-thinning effects. EPA and DHA act as blood thinners by inhibiting the formations of substances that promote blood clot formation. Fish oil supplements are available in capsule and liquid forms, and dosages vary by manufacturer.
Food sources of EPA and DHA include fatty fish, such as cod, salmon, sardines, tuna and mackerel. The American Heart Association notes that research data support daily consumption of 0.5 to 1.8 g of combined EPA and DHA to lower the risk of coronary heart disease. This equates to about 2 servings of fish weekly.
Vitamin E inhibits blood clot formation through a variety of mechanisms -- at least in the laboratory. This blood thinning effect appears to be dose dependent, meaning the effect may not be significant at low concentrations. More research is needed to determine whether there is a potential role for vitamin E as a natural blood thinner and, if so, to establish effective dosage recommendations. Vitamin E is found in a number of foods, including whole grains, wheat germ oil, almond oil, sunflower oil, egg yolks, seeds and nuts.
Coumarin Containing Herbs
The commonly prescribed blood thinning medication warfarin (Coumadin) is a derivative of the naturally occurring plant substance coumarin. More than 1,300 types of coumarins have been found in the metabolic processes of many plants, fungi and bacteria. It is a common misconception that natural occurring coumarins have comparable blood-thinning effects to the medication warfarin. However, no substantial evidence supports use of plant sources of coumarin as effective, safe blood-thinning agents.
Precautions and Interactions
In 2011, the Centers for Disease Control and Prevention found that over half of the adult population in the U.S. reports using dietary supplements. Discuss your medications, supplements and dietary choices with your healthcare provider as these may interact or have additive effects when combined with blood thinning medications. Don't stop taking your prescription anticoagulants or replace them with natural products without first consulting your healthcare provider.
Although many natural substances have blood thinning and clot prevention potential, research is needed to clarify the possible interactions, effective form and dosages before standardized health recommendations for natural blood thinners can be made.