Fish oil does not meaningfully increase your red blood cell count. Clinical trials measuring hemoglobin and hematocrit (two standard markers of red blood cell levels) have found no significant changes after fish oil supplementation, even at doses of 3 grams per day over two months. What fish oil does affect is the quality and flexibility of the red blood cells you already have, which is a different story worth understanding.
What the Clinical Evidence Shows
The most direct evidence comes from a controlled trial of patients taking 3 grams of omega-3 fatty acids daily for two months. Hemoglobin levels held steady at 11.0 g/dL in the fish oil group, compared to 11.46 g/dL dropping slightly to 11.37 g/dL in the placebo group. Hematocrit, which reflects the percentage of your blood volume occupied by red blood cells, also showed no change. The differences between groups were statistically meaningless.
A large randomized trial called VITAL, published through the American Society of Hematology, looked at omega-3 supplementation in a relatively healthy older adult population and found no overall reduction in anemia incidence. There was one notable exception: in participants who started the trial with elevated inflammation markers (C-reactive protein above 3 mg/L), omega-3s did produce a statistically significant effect on hemoglobin levels. This suggests fish oil may help maintain red blood cell levels specifically in people whose production is being suppressed by chronic inflammation, but it won’t boost counts in someone who is otherwise healthy.
How Fish Oil Changes Red Blood Cells
While fish oil won’t add more red blood cells to your bloodstream, it does change the ones you have. The omega-3 fatty acids EPA and DHA physically integrate into red blood cell membranes, displacing more rigid saturated fats. This makes each cell more flexible and fluid, a property called deformability. More deformable red blood cells squeeze through tiny capillaries more easily, which can improve blood flow to tissues.
This incorporation isn’t instant. In humans, EPA takes about 28 days to reach half its maximum concentration in red blood cell membranes, and DPA takes roughly 39 days. A single dose of fish oil, or even a large fish meal the day before a blood test, won’t change your red blood cell membrane composition at all. One study of healthy volunteers given 3.6 grams of omega-3s found that plasma levels of EPA and DHA jumped 47% within six hours, but red blood cell levels were completely unchanged even at 24 hours. This means consistent, daily supplementation over weeks is needed to see membrane changes.
Dose matters in a surprising way. Research in animal models found that low-dose fish oil (around 6 to 12.5% of dietary fat) improved red blood cell flexibility and reduced oxidative damage. But high doses actually reversed those benefits, increasing lipid peroxidation (a type of oxidative stress on cell membranes) and reducing red blood cell quality and lifespan. More is not better here.
Fish Oil and Oxygen Delivery in Athletes
Because more flexible red blood cells could theoretically deliver oxygen more efficiently, researchers have tested whether fish oil improves endurance performance. The results are mixed. In one study, cyclists taking EPA and DHA for eight weeks showed reduced heart rate and lower oxygen consumption during sustained submaximal exercise, suggesting their bodies were working more efficiently. Another study found that omega-3 supplementation increased nitric oxide levels, which correlated strongly with improvements in VO2 max (a measure of aerobic fitness).
But other trials found nothing. A study of 24 male cyclists taking about 1 gram of EPA and 0.75 grams of DHA for three weeks showed no changes in red blood cell characteristics, no difference in exercise performance, and no change in time-trial results. The pattern across studies suggests that any performance benefit likely comes from vascular improvements (better blood vessel function) rather than from changes in the red blood cells themselves. If your goal is to increase red blood cell count for athletic performance, fish oil is not the tool for that job.
The Inflammation Connection
The most promising line of research involves fish oil’s anti-inflammatory effects rather than any direct stimulation of red blood cell production. Chronic inflammation suppresses erythropoiesis, the process by which your bone marrow makes new red blood cells. It does this partly through a protein called hepcidin, which locks up iron and makes it unavailable for building hemoglobin. Omega-3 fatty acids reduce inflammatory signaling, which could theoretically release the brakes on red blood cell production in people with inflammatory conditions.
The VITAL trial’s finding supports this: omega-3s improved hemoglobin only in participants with measurably high inflammation. For someone with normal inflammatory markers, there’s no suppression to reverse, so fish oil has nothing to fix. This is why researchers are now looking at fish oil’s potential in populations with chronic kidney disease and autoimmune conditions, where inflammation-driven anemia is common.
Interactions With Other Blood-Building Nutrients
If you’re taking fish oil alongside iron or vitamin B12 supplements to address low red blood cell counts, there are no known interactions between omega-3s and these nutrients. Fish oil won’t block iron absorption or interfere with B12 metabolism. It also won’t enhance their absorption. The supplements work through completely separate pathways: iron and B12 provide raw materials for building hemoglobin and new red blood cells, while omega-3s modify the membranes of cells that already exist.
Fish oil does reduce platelet aggregation, making blood slightly less sticky. This is a separate effect from anything related to red blood cell count. It involves platelets (the clotting cells), not red blood cells, though the two are sometimes confused in casual conversation about “blood thinning.”
What This Means in Practice
If your red blood cell count is low and you’re hoping fish oil will raise it, the evidence says it won’t, at least not directly. The causes of low red blood cell counts (iron deficiency, B12 deficiency, chronic disease, bone marrow problems) require targeted treatment that fish oil cannot replace. Where fish oil may help is in a narrow situation: if your red blood cell production is being suppressed by chronic inflammation, omega-3s could reduce that inflammation enough to let your body produce red blood cells more normally. Even then, the effect is modest and has only been demonstrated in people with elevated inflammatory markers.
For general health, fish oil’s real value to your red blood cells is qualitative, not quantitative. It makes the cells you have more flexible and better at navigating your smallest blood vessels. To get this benefit, you need consistent daily supplementation for at least four to six weeks, and moderate doses appear to work better than high ones.