The association between omega-3 polyunsaturated fatty acids (PUFAs) and cardiovascular disease began in the 1970s with the Indigenous Peoples of Greenland. Epidemiologic examinations of the Greenland Inuit identified a connection between their high seafood consumption ( and omega-3s) and lower incidences of coronary heart disease (CHD) morbidity.
While the causes of CHD can vary, blood clots play a significant role in cardiovascular-related health outcomes such as heart attack, deep vein thrombosis (DVT), and stroke. It’s estimated that dangerous clotting conditions, such as DVT, affect as many as 900,000 people and kill up to 100,000 people in the U.S. annually. Yet, the public is generally unaware.
What are Blood Clots?
According to the Cleveland Clinic, a blood clot is a semi-solid mass of blood cells and other substances that form in your blood vessels. Blood clotting, or coagulation, is a necessary process that prevents excessive bleeding and acts as the first line of defense if the blood vessels are damaged. Whether you cut yourself shaving or are recovering from surgery, blood clots form to stop the bleeding. Similarly, in conditions such as atherosclerosis, hidden injury occurs in the blood vessels leading to plaque formation.
In some cases, the plaques fracture, triggering the body to form a clot at that site. Therefore, sometimes blood clots, also known as thrombus or embolus, can form without any obvious outward injury. Generally made of platelets and fibrin, these clot fragments and proteins work together to seal the injured vessels to protect the body. The body usually dissolves the blood clot when it is no longer needed to protect the injury site.
While blood clotting is necessary to protect from excessive bleeding, it can also be associated with adverse health outcomes. If a blood clot forms but does not dissolve naturally, it may become dangerous. Blood clots can inhibit blood flow, either partly or entirely, to specific body parts, preventing oxygen and nutrients from reaching the tissue in that area leading to tissue damage or death. If this occurs, it may lead to events such as heart attack, stroke, pulmonary embolism, or veinous thrombosis in the kidneys, legs, or arms, depending on where the clot forms.
What Causes Blood Clots?
Blood clots are more likely to form after an injury. Yet, some lifestyle choices or inherited conditions can also put someone at higher risk. Some circumstances that increase the risk for blood clots include:
- Sitting for long periods or being on bed rest
- During or after pregnancy
- When taking birth control or estrogen hormones
- After surgery or prior central line placement
- Smoking, obesity, or increasing age over 60
- Cancer, liver, or kidney disease
- Inherited conditions such as factor V Leiden mutation, prothrombin G20210A mutation, and elevated levels of fibrinogen or other blood factors influencing clotting
- Chronic inflammatory conditions such as diabetes, high cholesterol, high blood pressure, or autoimmune disorders
What are the Symptoms and Treatment Options for Blood Clots?
According to the American Society of Hematology, the symptoms of blood clots will depend on where the blood clot is located. Suppose a blood clot affects the heart muscle. In that case, a person might experience chest heaviness or pain, shortness of breath, sweating, light-headedness, or nausea.
If a blood clot affects the brain, a person might notice weakness of the face, arms, or legs, difficulty speaking, vision problems, headaches, and dizziness. If the extremities are affected, there will likely be gradual pain, swelling, tenderness, and warmth in the affected area.
When blood clots affect the lungs, there may be sharp chest pain, shortness of breath, increased heart rate, sweating, fever, or coughing up blood.
Just as the symptoms are different depending on the affected area, so is the treatment. Some current treatments include medications such as anticoagulants and thrombolytics, which can help prevent clots from forming and dissolve already-formed clots.
Or there are surgical procedures such as catheter-directed thrombolysis, in which a long tube is inserted and directed toward the blood clot to deliver clot-dissolving medication. Similarly, a thrombectomy is the surgical removal of a blood clot.
The good news is there are several ways to decrease your chances of developing a blood clot, even if you fall under a high-risk group.
Fish Oil’s Many Health Benefits
Fish oil is a dietary source of omega-3 fatty acids DHA and EPA. According to the National Institutes of Health (NIH) Office of Dietary Supplements, higher intake of omega-3 fatty acids is associated with a lower risk of several adverse health outcomes and chronic diseases related to:
- Infant health and development
- Cancer prevention
- Alzheimer’s disease, dementia, and cognitive function
- Age-related macular degeneration
- Rheumatoid arthritis
- Cardiovascular disease
Does Fish Oil Prevent Blood Clots?
The beneficial effects of dietary omega-3s on cardiovascular disease are multifactorial and may partly rely on their anticoagulant action. Evidence in human studies demonstrates that omega-3 fatty acids influence blood characteristics.
A meta-analysis of 15 randomized controlled trials in humans revealed that, compared to a placebo, omega-3 supplementation significantly reduced platelet aggregation in participants with poor health status. Since increased platelet activity predicts adverse cardiovascular events, the authors concluded that high-risk patients with cardiovascular disease or diabetes may benefit from omega-3 therapy. However, not just people with poor health may benefit; several studies have also been performed in healthy populations.
A large population-based study conducted in Norway found that a high weekly fish intake was associated with a 22% lower risk of venous thromboembolism compared to those who consumed low fish and no omega-3 supplementation. Adding fish oil supplements strengthened the inverse effect leading to a 48% lower risk.
Another study conducted in healthy males found that 3 grams of fish oil supplementation daily for four weeks provoked a hypocoagulant effect, which varied depending on fibrinogen levels. Furthermore, omega-3s have been found to reduce whole blood viscosity, improve red blood cell flexibility, and decrease plasma viscosity and systolic blood pressure. Other studies in healthy individuals found that omega-3s enhanced anticoagulant properties by reducing platelet activation, adhesiveness, and aggregation.
Both EPA and DHA improve coagulating outcomes by incorporating into platelet phospholipids at the expense of other fatty acids, such as the omega-6 fatty acid arachidonic acid (AA). This replacement may help reduce platelet aggregation by reducing AA-derived procoagulant metabolites and competing for enzymes required for activation. Furthermore, EPA and DHA get incorporated into neutrophils and red blood cells at the expense of other fatty acids, leading to decreased whole blood viscosity and increased red blood cell flexibility, reducing the risk of thrombosis.
Finally, although evidence indicates that omega-3 intake can reduce clotting, current literature suggests that no additional bleeding risks exist. A 2007 publication concluded that omega-3s do not increase the risk of clinically significant bleeding, even in patients treated with antiplatelet or antithrombotic medications. Likewise, a 2018 study confirmed these findings, concluding that omega-3 supplementation did not increase the risk of perioperative bleeding and unexpectedly significantly reduced the number of units of blood transfused.
Fish Oil Recommendations
EPA and DHA can be increased in the diet by consuming fatty fish such as salmon, mackerel, anchovies, herring and sardines, which are otherwise known as the SMASH fish. Research indicates that including ~17 oz of oily fish per week for four weeks can significantly reduce platelet-monocyte aggregates by 35%, which is reverted to baseline four weeks after discontinuation.
However, if increasing fish in the diet is unrealistic, supplementation is another valuable option. While subject matter experts have yet to establish recommended amounts for omega-3 fatty acids, evidence suggests that 2-4 grams of EPA/DHA per day is needed to provide antiatherosclerotic, anti-inflammatory, and antiplatelet benefits. Some studies have used up to 6 grams per day and found that while the omega-3s appeared in the plasma after 4 hours, they were not incorporated into platelet phospholipids until day 6. However, some studies indicate that supplementing for a minimum of 18 weeks, and possibly longer, may be needed to receive antithrombotic effects.
Although intake of both EPA and DHA inhibits platelet aggregation, DHA has a faster onset of action than EPA. This was demonstrated in a double-blind placebo-controlled trial including 59 patients with hypertension when they were provided either 4 grams/day EPA, DHA, or olive oil (placebo).
The researchers found that DHA is more effective than EPA at reducing platelet aggregation, reversing impaired fibrinolysis, and improving endothelial dysfunction. Yet, that does not mean that EPA is not helpful. An extensive study including over 8,000 patients with elevated triglyceride levels significantly decreased the risk of ischemic events, including cardiovascular death, with EPA supplementation compared to a placebo. Both EPA and DHA combined are likely to provide value. For more information on choosing the best omega-3 supplement for you, check out this recent article.
Hundreds of thousands of people are affected by adverse cardiovascular-related conditions correlated to blood clotting each year. There are many causes for blood clots, and the signs and symptoms will vary based on where the blood clot occurs.
Omega-3 fatty acids have many health benefits, including anticoagulant and antiplatelet effects. Human studies confirm that adequate intake (2-4 grams DHA/EPA daily) of omega-3 fatty acids regularly decreases the risk of clotting and other cardiovascular risk factors. Although there are ways to decrease the risk of blood clots and several treatment options if one develops, blood clots can be life-threatening. If you suspect a blood clot, see a doctor immediately.