Fish oil does appear to help with circulation through several overlapping mechanisms. The two omega-3 fatty acids in fish oil, EPA and DHA, make blood less viscous, reduce platelet clumping, relax blood vessel walls, and decrease arterial stiffness. The effects are modest in healthy people but more pronounced in those with existing circulatory problems.
How Fish Oil Affects Blood Flow
Fish oil improves circulation through at least three distinct pathways, each targeting a different part of the system that moves blood through your body.
First, omega-3s change the physical properties of your red blood cells. When healthy volunteers took 3 grams of omega-3s daily, their red blood cells became more deformable, meaning the cells could squeeze through tiny capillaries more easily. This led to a measurable reduction in whole blood viscosity. Thinner blood flows more readily, particularly through the smallest vessels in your fingers, toes, and organs. The researchers found that plasma thickness and red blood cell count stayed the same, so the improvement came specifically from the cell membranes becoming more flexible as they incorporated omega-3 fats.
Second, EPA and DHA help blood vessels relax. The cells lining your arteries produce nitric oxide and other signaling molecules that tell the surrounding muscle to loosen up, widening the vessel and letting more blood pass. Omega-3s boost the availability of nitric oxide, and lab studies show both EPA and DHA cause dose-dependent relaxation in arteries. The exact pathway is still debated. Some evidence points to increased production of the enzyme that makes nitric oxide, while other research suggests omega-3s work through additional relaxation pathways independent of that enzyme.
Third, omega-3s make platelets less sticky. Platelets are the blood cells responsible for clotting, but when they’re overly active, they can clump together and slow circulation or contribute to blockages. Both DHA and EPA inhibit platelet aggregation in a dose-dependent manner. They do this partly by competing with a pro-inflammatory fat (arachidonic acid) for the same enzymes, shifting the balance away from molecules that promote clumping and toward ones that don’t.
Arterial Stiffness and Aging
As you age, your arteries naturally stiffen, which forces your heart to work harder and reduces efficient blood delivery. Fish oil supplementation reduced a key measure of central arterial stiffness (called pulse wave velocity) by about 9% in older adults. In practical terms, the speed at which pressure waves travel through the main artery dropped from 988 cm/sec to 895 cm/sec after supplementation. That roughly 93 cm/sec reduction is considered large enough to be clinically meaningful. Younger adults in the same study saw no significant change, likely because their arteries were already flexible.
Cold Hands and Raynaud’s Phenomenon
If your circulation concern involves fingers or toes that go white and numb in cold weather, fish oil has some of the most striking evidence. In a double-blind trial of people with Raynaud’s phenomenon, those taking fish oil could tolerate cold exposure for a median of 46.5 minutes before symptoms appeared, up from 31.3 minutes at baseline. That’s roughly 15 extra minutes of cold tolerance. Among those with primary Raynaud’s (the kind not caused by another disease), 45% of fish oil users could no longer be triggered into an episode at all by the end of the study, compared with just 11% in the placebo group. Digital blood pressure in cold water was 32 mmHg higher in the fish oil group, meaning their finger arteries stayed more open. These benefits did not extend to people whose Raynaud’s was secondary to another condition like lupus or scleroderma.
Peripheral Artery Disease
For people with narrowed leg arteries that cause pain while walking, the picture is less clear. A meta-analysis found that omega-3 supplementation does reduce blood viscosity in this population, but the evidence doesn’t show a significant improvement in walking distance or ankle blood pressure measurements. Some individual studies have found walking improvements, with at least one showing the benefit depended on body weight and inflammatory genetics. Research is ongoing, with trials like the OMEGA-PAD study specifically testing whether high-dose, short-term omega-3 supplementation can improve how well blood vessels dilate in people with symptomatic peripheral artery disease.
What the Heart Association Recommends
The American Heart Association recommends one to two servings of seafood per week for general heart and vascular health, particularly when fish replaces less healthy protein sources. For people with existing coronary heart disease, the AHA suggests about 1 gram per day of combined EPA and DHA, preferably from oily fish. The AHA does not recommend omega-3 supplements for people without elevated cardiovascular risk.
For lowering triglycerides (a blood fat that affects vascular health), the therapeutic dose is 4 grams per day of prescription omega-3s. A large meta-analysis of cardiovascular trials used doses ranging from 0.4 to 5.5 grams per day and found omega-3s reduced cardiovascular mortality by 7%, non-fatal heart attacks by 13%, and coronary heart disease events by 9%. EPA-only formulations showed larger reductions than combined EPA and DHA across most outcomes.
The Bleeding Question
Because fish oil makes blood less sticky and more fluid, a common concern is whether it increases bleeding risk. This worry has led many surgeons to recommend stopping fish oil before procedures. However, a large placebo-controlled trial of over 1,500 cardiac surgery patients found that fish oil supplementation (at doses of 8 to 10 grams in the days before surgery, then 2 grams daily after) did not increase perioperative bleeding. In fact, patients who achieved the highest omega-3 blood levels had a 64 to 70% lower risk of major bleeding compared to those with the lowest levels, and the fish oil group needed fewer blood transfusions overall. These findings have prompted calls to reconsider the standard advice to stop fish oil before surgery.
At typical supplement doses of 1 to 3 grams daily, bleeding risk is not a practical concern for most people. The FDA considers up to 5 grams per day of EPA and DHA from supplements to be generally safe.
Getting Enough From Food vs. Supplements
A 3-ounce serving of salmon provides roughly 1.5 grams of EPA and DHA combined. Sardines, mackerel, herring, and anchovies are similarly rich sources. Two servings per week puts you in the range the AHA recommends for general cardiovascular health, delivering somewhere around 500 mg of omega-3s per day on average.
Supplements become more relevant if you’re targeting a specific circulatory issue. The studies showing benefits for blood viscosity, arterial stiffness, and Raynaud’s used doses of 2 to 3 grams of EPA plus DHA daily, which is difficult to get from diet alone unless you eat fatty fish almost every day. If you go the supplement route, check the label for the actual EPA and DHA content per serving, not just “fish oil.” A 1,000 mg fish oil capsule typically contains only 300 mg of combined EPA and DHA, so you may need several capsules to reach a meaningful dose.