Grapefruit is a nutritious citrus fruit commonly eaten or squeezed for its juice for breakfast. Grapefruit juice has little ability to thin your blood on its own, but it can react with blood-thinning medications and make them more potent. Thin blood refers to the inability of your blood platelet cells to clump together and form blood clots, which is essential to heal wounds. Some conditions, such as atherosclerosis, may benefit from thinner blood, but other conditions, such as stomach ulcers or aneurysms, may be compounded. Consult with your doctor about which drugs are affected by grapefruit juice.
Natural Blood Thinners
Natural blood thinners display anti-coagulant properties, which deter platelet cells in your blood from aggregating and forming clots. Natural blood thinners can be divided into four categories: foods that contain salicylates, foods rich in vitamin E, foods that contain omega-3 fatty acids and foods that display antibiotic properties, according to the textbook “Advanced Nutrition and Human Metabolism.” Grapefruit juice contains trace amounts of salicylates and displays antibiotic properties.
Salicylates are aspirin-like compounds that block vitamin K absorption. Your body needs vitamin K to initiate the coagulation cascade, which is a series of biochemical reactions culminating with the formation of blood clots. Foods that are high in salicylates include many spices, most fruits -- especially dried varieties -- and many nuts. According to the textbook “Biochemistry of Human Nutrition,” grapefruit juice does not contain many salicylates, but it does contain trace amounts.
Grapefruit juice is a fairly rich source of citric acid, which is an important substance for human metabolism, but it also displays antibiotic properties that may reduce bacterial colonies in your intestines, according to the textbook “Biochemical, Physiological and Molecular Aspects of Human Nutrition.” Some bacteria in your intestines are considered beneficial because they produce vitamin K, which is needed for blood coagulation. Excessive levels of citric acid may disrupt these beneficial colonies and hamper vitamin K production and absorption. Further, citric acid has a natural affinity for calcium and binds to it, which tends to inhibit the coagulation cascade because it depends on calcium ions within your blood to proceed, according to “Medical Nutrition and Disease.”
Grapefruit Juice and Medications
One regular glass of grapefruit juice is enough to severely affect the way your body reacts to medications, especially if they are taken within four hours of each other, according to the book “Nutritional Sciences.” Grapefruit juice inhibits the CYP3A4 enzyme, which is used by your body to metabolize certain drugs. Potentially dangerous interactions with grapefruit juice include blood-thinning medications such as Coumadin. Taken together, grapefruit juice may make Coumadin much more biologically active than your doctor intends, which increases the risks of hemorrhagic strokes, internal bleeding, bruising, nose bleeds and heavy menstrual flow.