Blood thickness, known medically as viscosity, is determined almost entirely by two factors: the concentration of red blood cells in your blood (hematocrit) and the level of proteins dissolved in your plasma. Of these two, hematocrit is by far the dominant one, with a near-perfect correlation to overall viscosity. The good news is that several practical, everyday strategies can meaningfully lower blood viscosity and improve circulation.
What Makes Blood Thicker
Your blood is not a uniform liquid. It’s a suspension of cells, clotting proteins, and plasma, and the balance between these components determines how easily it flows. When researchers measure blood viscosity, hematocrit alone accounts for roughly 98% of the variation between people. Plasma proteins, particularly fibrinogen (a clotting protein), play a smaller but still meaningful role. Anything that raises red blood cell concentration or increases clotting proteins in your bloodstream will make your blood thicker and harder for your heart to pump.
Several conditions push viscosity higher: dehydration, smoking, chronic inflammation, and certain blood disorders. Understanding which factor is driving your own blood thickness helps you choose the most effective approach to bringing it down.
Stay Consistently Hydrated
Dehydration is the fastest, most common way blood gets thicker. When you lose fluid without replacing it, plasma volume drops and the same number of red blood cells are packed into less liquid. In one study measuring what happens when people sit in a dry environment for four hours without drinking, plasma volume fell by 3.4% within two hours and blood viscosity jumped by 9.3%. That’s a significant change from simply not drinking water on a dry afternoon.
The same study found that drinking water beforehand completely prevented the viscosity increase. You don’t need a special beverage or electrolyte formula. Plain water retained about 38% of consumed fluid after two hours, which was enough to keep blood viscosity stable. The practical takeaway: drink water consistently throughout the day rather than waiting until you feel thirsty, especially in dry or warm environments, during flights, or when sitting for long periods.
Exercise Regularly at Moderate Intensity
Aerobic exercise is one of the most effective long-term strategies for reducing blood viscosity. A study of participants doing moderate-intensity aerobic exercise for 40 to 45 minutes, three times a week over 9 to 12 weeks found a statistically significant decrease in blood viscosity of about 3%.
The mechanism is straightforward. Regular cardio training increases your total plasma volume, meaning your body holds more liquid in the bloodstream while the number of red blood cells stays roughly the same. This dilution effect lowers hematocrit and makes blood flow more easily. The benefit builds over weeks of consistent training, so a single jog won’t change much, but a sustained routine will. Walking, cycling, swimming, and jogging all qualify as long as you’re working at a moderate effort level.
Quit Smoking
Smoking thickens blood through two separate pathways at once. First, carbon monoxide from tobacco smoke binds to red blood cells and reduces their ability to carry oxygen. Your body detects the oxygen shortage and responds by producing more red blood cells to compensate, raising your hematocrit. Second, smoking simultaneously shrinks your plasma volume, concentrating the blood cells you already have into less fluid. The combination of more red blood cells and less plasma creates a condition called smoker’s polycythemia, which significantly raises viscosity and puts you at risk for blood clots and stroke.
This effect is dose-dependent and reversible. Quitting smoking allows plasma volume to normalize and stops the signal that drives excess red blood cell production.
Foods and Spices With Blood-Thinning Properties
Several common foods have measurable effects on how blood clots and flows, though the evidence varies in strength.
Turmeric contains curcumin, which has demonstrated real anticoagulant activity in both lab and animal studies. Curcumin slows clotting by inhibiting two key enzymes in the coagulation cascade, the same targets that prescription blood thinners act on. Researchers have noted that regular consumption of turmeric in food may help maintain a mild anticoagulant effect, though concentrated supplements deliver far more curcumin than curry alone.
Garlic has mixed clinical evidence. Some human trials show a clear reduction in platelet clumping after several weeks of aged garlic extract (typically 800 mg doses taken multiple times daily), while others using raw garlic or oil extracts found no significant effect. The form and dose matter. Aged garlic extract taken consistently over weeks appears more reliable than raw garlic eaten occasionally. In one trial lasting 11 months, aged garlic extract produced measurable inhibition of platelet activity. A shorter trial using powdered garlic tablets for just four weeks also showed a significant reduction in circulating platelet clumps compared to placebo.
Ginger is often cited as a blood thinner, but its antiplatelet effects have mostly been demonstrated in lab settings, not in randomized human trials. It may have some benefit, but the evidence is weaker than for garlic or turmeric.
Nattokinase
Nattokinase, an enzyme derived from a traditional Japanese fermented soybean dish called natto, has attracted attention for its ability to dissolve fibrin, the protein mesh that forms the structural backbone of blood clots. Unlike most natural compounds, nattokinase works through multiple mechanisms: it breaks down fibrin directly, boosts your body’s own clot-dissolving system by increasing the release of natural clot-busting agents, and it inactivates a protein that normally blocks clot breakdown. Some researchers have described its potential as superior to aspirin for improving blood flow, though it remains a supplement rather than a regulated medication.
When Prescription Blood Thinners Are Used
For people with diagnosed cardiovascular conditions, prescription medications go much further than lifestyle changes. There are two main categories, and they work differently.
Antiplatelet drugs reduce the stickiness of platelets, the tiny cell fragments that clump together to start a clot. Anticoagulants interfere with the clotting cascade itself, the chain reaction of proteins that builds a clot into a solid mass. Newer oral anticoagulants combined with a single antiplatelet drug may offer the best balance between preventing dangerous clots and avoiding excessive bleeding risk, particularly for people with acute coronary conditions.
Low-dose aspirin, the most familiar over-the-counter blood thinner, has seen its recommendations narrow in recent years. Current U.S. Preventive Services Task Force guidelines say adults aged 40 to 59 with a 10% or greater ten-year cardiovascular risk can consider daily low-dose aspirin (81 mg), but only after weighing the small net benefit against bleeding risk. For adults 60 and older, the recommendation is clear: do not start aspirin for primary prevention. The bleeding risks at that age outweigh the cardiovascular benefits for people who haven’t already had a heart attack or stroke.
Important Safety Considerations
Anything that effectively thins your blood also increases your risk of bleeding, whether it’s a prescription drug, a supplement, or a dietary habit. This becomes especially important before surgery. Most hospitals ask patients to stop supplements like garlic, vitamin E, and turmeric at least seven days before any scheduled procedure. Fish oil, ginkgo, and nattokinase typically fall under the same guidance.
Combining multiple blood-thinning strategies can compound the effect in ways that are hard to predict. Taking a turmeric supplement alongside prescription anticoagulants, for example, could push your clotting ability lower than intended. If you’re already on blood-thinning medication, adding supplements with anticoagulant or antiplatelet properties requires careful coordination with whoever manages your prescriptions.
For most people without a diagnosed clotting disorder, the foundational strategies are simple: stay well hydrated, exercise consistently, don’t smoke, and include naturally anticoagulant foods like turmeric and garlic in your regular diet. These steps lower viscosity through the same biological pathways that medications target, just more gently.