Can drinking water reduce blood thickness? A look into hydration and hemorheology

October 7, 2025 •

3 min read

Blood is approximately 55% plasma, which is primarily water, making proper hydration fundamental to its consistency. This relationship directly influences how can drinking water reduce blood thickness, particularly in preventing the temporary effects of dehydration and maintaining optimal cardiovascular function.

Quick Summary

Maintaining adequate hydration helps prevent temporary increases in blood thickness by sustaining optimal blood plasma levels. While beneficial for general circulation, drinking water is not a medical treatment for chronic blood disorders that cause high blood viscosity.

Key Points

Viscosity Defined: Blood viscosity is its thickness and stickiness, directly impacting how hard your heart works to circulate blood.
Dehydration's Impact: Dehydration reduces blood plasma, concentrating blood components and temporarily increasing viscosity, putting strain on the heart.
Water's Role: Drinking water helps prevent dehydration and restore optimal plasma volume, thereby reducing temporary blood thickening.
Not a Medical Cure: Water is not a treatment for chronic blood-thickening conditions like Polycythemia Vera, which require professional medical intervention.
Stay Proactive: Recognizing the signs of dehydration and consistently drinking water throughout the day are key to maintaining healthy blood viscosity.

What is blood viscosity and why does it matter?

Blood viscosity is a measure of the thickness and stickiness of your blood, or its resistance to flow. It is an important factor in cardiovascular health, as higher viscosity makes the heart work harder to pump blood throughout the body. Key determinants of blood viscosity include the ratio of red blood cells to plasma (hematocrit), plasma protein concentration, and red blood cell flexibility. Maintaining optimal viscosity is crucial for efficient blood circulation and oxygen delivery to your tissues and organs.

The powerful impact of hydration on blood viscosity

When you are adequately hydrated, your blood plasma volume remains at an optimal level, keeping your blood sufficiently dilute and promoting smooth, efficient blood flow. The effects of dehydration, however, are immediate and significant. Even mild dehydration can reduce your plasma volume, causing your blood to become thicker and more viscous. This hemoconcentration puts added strain on your heart and can increase the risk of blood clots, especially during prolonged periods of immobility. Conversely, simply drinking water helps restore your plasma volume and reduce this temporary increase in blood thickness caused by dehydration.

It's important to distinguish between water's preventative role and its limitations. For individuals without an underlying medical condition, maintaining hydration is a primary way to manage blood viscosity within a healthy range. However, for those with medical conditions affecting blood thickness, water is not a substitute for professional medical treatment.

Hydration-related vs. medically-induced blood thickening

For a clear understanding of the role of water, it's essential to differentiate between blood thickening caused by dehydration and that caused by a chronic medical condition. The table below outlines these key distinctions:


Feature	Dehydration-Induced Blood Thickening	Medically-Induced Blood Thickening
Cause	Low fluid intake, sweating, illness leading to reduced plasma volume.	Chronic conditions such as Polycythemia Vera, Multiple Myeloma, or certain genetic disorders.
Onset	Acute and temporary, resolving with adequate rehydration.	Chronic and persistent, often requiring ongoing medical management.
Mechanism	Decreased plasma volume concentrates red blood cells and other blood components.	Overproduction of blood cells or proteins, leading to higher hematocrit or protein levels.
Resolution	Drinking water or other fluids to restore fluid balance.	Requires specialized medical treatment, such as phlebotomy, chemotherapy, or other targeted therapies.
Health Risk	Increased risk of clots, especially in risk-prone situations like long flights.	Sustained risk of clots, stroke, heart attack, and other complications.

Recognising the signs of dehydration

To proactively manage your hydration and prevent temporary blood thickening, it's crucial to recognise the signs of dehydration. Common symptoms include:

Increased thirst
Dark yellow or strong-smelling urine
Reduced urination frequency
Fatigue and dizziness
Headache
Dry mouth, lips, and eyes
Confusion or lightheadedness

Practical tips for staying optimally hydrated

Drink consistently throughout the day: Don't wait until you are thirsty, as thirst is a sign you are already slightly dehydrated. Keep a water bottle with you and sip frequently. The American Heart Association recommends carrying a reusable water bottle to make drinking water easier.
Start and end your day with water: Drink a glass upon waking and another before bed to maintain hydration overnight.
Include water-rich foods in your diet: Fruits and vegetables like watermelon, cucumbers, strawberries, and celery contribute significantly to your daily fluid intake.
Tailor your intake to your activity level: Increase your fluid consumption when exercising, especially in hot weather, to compensate for fluid loss through sweat.
Choose hydrating beverages wisely: While water is best, other beverages like plain tea, coffee, and milk can contribute to hydration. However, be mindful of diuretics like alcohol and excessive caffeine, which can lead to fluid loss.

Conclusion

In conclusion, drinking water is an effective and necessary strategy for preventing the temporary increase in blood thickness caused by dehydration. By maintaining proper hydration, you support optimal blood viscosity, reduce strain on your heart, and promote efficient circulation. It is crucial to remember, however, that water is not a medical treatment for chronic blood disorders. Individuals concerned about persistent blood thickness should consult a healthcare professional for diagnosis and appropriate management. By staying hydrated, you empower your body's natural systems to function effectively and support long-term cardiovascular health. For further information on the effects of dehydration, you can visit the National Institutes of Health (NIH) at https://newsinhealth.nih.gov/2023/05/hydrating-health.

Frequently Asked Questions

A general guideline is about 8 glasses (2 liters) per day, but individual needs vary based on factors like activity level, climate, and body size. A good practice is to drink when you feel thirsty and maintain light-colored urine.

Yes, staying well-hydrated helps maintain proper blood viscosity, which promotes smoother blood flow and may reduce the risk of clot formation associated with dehydration. However, it is not a cure or preventative measure for blood clots caused by other medical conditions.

Yes, it is possible, though uncommon, to overhydrate. This can lead to a condition called hyponatremia, where sodium levels in the blood become dangerously low. Symptoms can include confusion, nausea, and headaches. It is best to listen to your body's thirst signals.

Symptoms of dehydration include thirst, dark-colored urine, infrequent urination, fatigue, dizziness, and headache.

For most people, water is the best choice for hydration. Sports drinks are formulated for intense exercise and contain electrolytes and sugars, which may not be necessary and can contribute to excess calorie intake for light activity.

If you have concerns about chronic blood thickness or viscosity, you should consult a healthcare professional. They can properly diagnose any underlying medical condition and provide appropriate treatment, as drinking water alone will not be a sufficient remedy.

Yes, many fruits and vegetables have high water content and contribute significantly to your daily hydration. Examples include watermelon, strawberries, cucumbers, and leafy greens.