Blood viscosity, or how thick and resistant to flow your blood is, can be lowered through a combination of hydration, diet, exercise, and targeted supplements. The key drivers of viscosity are the volume of red blood cells in your blood (hematocrit), the concentration of proteins like fibrinogen in your plasma, and how easily your red blood cells can bend and squeeze through small vessels. Each natural strategy works by targeting one or more of these factors.
What Makes Blood Thick
Your blood’s thickness comes down to a few measurable components. The most influential is hematocrit, the percentage of your blood volume occupied by red blood cells. More red blood cells mean thicker blood, and the relationship is direct and linear. The second major factor is plasma viscosity, which rises when proteins like fibrinogen and globulins accumulate at higher-than-normal concentrations. Any elevation in these proteins thickens both your plasma and your whole blood.
A third, less obvious factor is red blood cell flexibility. Healthy red blood cells are remarkably deformable, folding and squeezing through capillaries narrower than they are. When they stiffen, from oxidative stress, poor diet, or chronic inflammation, blood flows less freely. Red blood cell aggregation also plays a role: cells that clump together create more resistance, especially during the slow-flow phase between heartbeats.
Stay Consistently Hydrated
Dehydration is the fastest way to thicken your blood. When your body loses fluid, plasma volume drops and red blood cells become more concentrated, pushing viscosity up. Research on prolonged sitting in dry environments found that participants who did not prehydrate showed a measurable decline in plasma volume and a corresponding rise in blood viscosity within just two to three hours. Those who drank an electrolyte-containing beverage beforehand maintained baseline viscosity throughout the same period, while plain water was somewhat less effective at holding plasma volume steady.
The practical takeaway: don’t wait until you’re thirsty. Sip water throughout the day, and if you’re in a dry environment, flying, or exercising, add a drink with electrolytes. Sodium helps your body retain the fluid in your bloodstream rather than simply passing it through your kidneys.
Omega-3 Fatty Acids
Omega-3s from fish oil are among the most studied natural interventions for blood viscosity. In a placebo-controlled, double-blind trial, omega-3 fatty acids in gradually increasing doses produced a stepwise improvement in blood flow properties. After 21 days of supplementation, plasma viscosity dropped significantly. By 56 days, whole blood viscosity had decreased and red blood cell deformability had improved, meaning cells could flex more easily through narrow vessels. At higher doses, red blood cell aggregation also declined.
These effects come from EPA and DHA competing with omega-6 fatty acids in your body’s inflammatory pathways, shifting the balance away from compounds that promote clotting and stiffness. You can get omega-3s from fatty fish like salmon, mackerel, and sardines, or from a concentrated fish oil supplement. Most studies showing blood flow benefits use doses in the range of 2 to 4 grams of combined EPA and DHA per day, which is higher than what a casual fish-eater typically gets.
Regular Aerobic Exercise
Endurance exercise, cycling, running, swimming, or brisk walking, triggers one of the most reliable natural mechanisms for reducing blood viscosity: plasma volume expansion. When you train consistently, your body adapts by increasing the amount of plasma in your bloodstream. This dilutes the concentration of red blood cells and proteins, effectively thinning the blood. The adaptation also increases total body water content over time, making you more resilient to the dehydrating effects of heat and exertion.
Both moderate steady-state cardio and high-intensity interval training produce this effect. One study found that high-intensity intervals improved the acute plasma volume response to exercise in a way that varied by age but was present across groups. You don’t need to run marathons. Consistent aerobic activity several times a week is enough to stimulate the plasma volume expansion that keeps viscosity in a healthier range.
Nattokinase
Nattokinase is an enzyme extracted from natto, a traditional Japanese fermented soybean food. It acts as a potent fibrinolytic agent, meaning it breaks down fibrinogen, one of the plasma proteins most responsible for making blood thick and clot-prone. Lab research has confirmed that nattokinase reduces red blood cell aggregation and whole blood viscosity directly.
A large clinical study with 1,062 participants tested nattokinase at two doses over 12 months. The higher dose of 10,800 FU per day significantly reduced triglycerides by about 15.5% and slowed the progression of arterial plaque. The lower dose of 3,600 FU per day, which is closer to what many commercial supplements contain, was ineffective for both lipid levels and atherosclerosis. This is a notable gap: the dose that actually works in clinical research is roughly three to five times higher than what’s commonly recommended in Europe and on many supplement labels. If you’re considering nattokinase, the dosing details matter considerably.
Curcumin and Garlic
Curcumin, the active compound in turmeric, has shown cardiovascular benefits in clinical trials, though the evidence for viscosity specifically is more indirect. In postmenopausal women, 150 mg of a highly bioavailable curcumin form taken daily for eight weeks improved arterial compliance (how well arteries expand and contract) and reduced measures of arterial stiffness. When combined with regular exercise, the same dose lowered the workload on the heart and reduced central blood pressure. A longer trial using 500 mg of curcuminoids with piperine (black pepper extract, which dramatically improves absorption) for 24 weeks reduced markers of hypercoagulability, meaning blood was less prone to excessive clotting.
Garlic has a well-documented ability to inhibit platelet aggregation, the tendency of platelets to clump together and form clots. This doesn’t lower viscosity in the traditional sense of thinning plasma, but it improves how blood flows through vessels by reducing the stickiness of its cellular components.
Vitamin E and Platelet Stickiness
Vitamin E (alpha-tocopherol) inhibits platelet aggregation triggered by several of the body’s main clotting signals, including thrombin, collagen, and ADP. Lab studies have confirmed this effect consistently. In human supplementation research, 400 IU per day inhibited platelet adhesion to various surfaces by more than 75%. Interestingly, higher doses up to 1,200 IU per day did not further improve platelet aggregation when used alone, though they did reduce adhesion, suggesting there’s a ceiling to the benefit.
Vitamin E is fat-soluble and accumulates in the body, so more is not necessarily better. Doses above 400 IU daily have been associated with increased bleeding risk in some populations, particularly in combination with other blood-thinning agents.
Blood Donation
Donating blood is a surprisingly direct way to lower viscosity. A standard donation removes about one pint of blood, which immediately reduces hematocrit. In one study, blood viscosity measured at a high shear rate dropped from an average of 4.53 to 4.18 centipoise after a single donation, a statistically significant reduction. Your body replaces the lost plasma within 24 to 48 hours, but red blood cell replacement takes several weeks, so the diluting effect persists for some time. If you’re eligible to donate, doing so a few times a year offers a measurable viscosity benefit alongside the obvious community value.
Interactions With Blood-Thinning Medications
If you take prescription anticoagulants like warfarin, combining them with natural blood-thinning supplements can be dangerous. Garlic and ginkgo biloba both increase bleeding risk by further inhibiting platelet aggregation on top of the drug’s effects. Herbs containing natural coumarin compounds, including licorice, passionflower, and arnica, can amplify warfarin’s action and push your clotting time into an unsafe range. Dan Shen and Dang Gui, two herbs common in traditional Chinese medicine, have also been documented to enhance warfarin’s effect significantly.
Conversely, some supplements can reduce your anticoagulant’s effectiveness. Green tea, ginseng, aloe vera, and bilberry juice have all been linked to drops in INR (a measure of how well your anticoagulant is working) in people on warfarin. Even a daily multivitamin containing vitamin E and fish oil has triggered this interaction. The core issue is unpredictability: these substances shift your clotting balance in ways that are difficult to dose-match with your medication. If you’re on any anticoagulant, work with your prescriber before adding supplements that affect blood flow.