Does Water Thin Your Blood and Prevent Blood Clots? The Answer Is Not So Clear

Blood clots are your body’s natural way to prevent bleeding when a blood vessel is injured. But sometimes, these clots can form in a vein for different reasons. For example, they can form during a long airplane flight when you are not able to move around. Or they can occur if you have a condition that causes swelling in the legs. 

When this happens, you can develop something called a deep vein thrombosis (DVT). These are blood clots that form where they are not supposed to and then don’t go away on their own. They can be serious. If you are at increased risk for a blood clot, there are simple things you can do to help prevent them. But is drinking water one of them? Let’s take a look at how hydration affects your blood. 

Does drinking water increase blood flow?

There are two main ways that drinking water can increase blood flow. It:

1. Expands blood volume

2. Triggers an automatic response by your body that adjusts your blood flow

Let’s go through these one at a time.

First, hydration increases the amount or “volume” of water in your blood vessels. Imagine your blood vessels are like pipes flowing from the kitchen sink. When you open the faucet (drink water), more fluid will flow through the pipes. 

Your blood volume is determined by more than just how much water you drink. It is also affected by things like how much you urinate and sweat — even the amount of electrolytes like salt in your blood. 

Second, drinking water can also trigger a “pressor response” in the body. This automatic response changes your heart rate and blood pressure to ensure you are getting enough blood flow to vital organs — like your brain, heart, lungs, and kidneys. And for people who have problems with low blood flow, drinking water can trigger this response. In other words, it improves their blood pressure and blood flow. 

Does drinking water prevent blood clots?

Since drinking water affects blood flow, it makes sense that it would prevent blood clots. But even though experts often suggest people drink water to prevent blood clots, the research does not show this for sure. 

To understand the reasoning behind their advice, it helps to first understand a little bit about how a DVT can form. 

When there is decreased flow through the veins — maybe because someone can’t walk — blood can start to pool in the veins rather than flow forward. This pooling increases the chances that clotting substances in the blood start to stick together. This process can form a clot. 

So, anything that improves blood flow — like walking around or drinking water — can help the blood move forward and in theory prevent clots. 

But researchers aren’t convinced that drinking water makes a meaningful difference. In fact, one study concludes that how much a person drinks makes no difference in the thickness of their blood (and its likelihood of clotting).

Some researchers think that drinking water only makes a difference in a person’s blood thickness if they are dehydrated to begin with. One study shows that dehydration leads to:

• Increased activity of an enzyme that plays a role in the development of blood clot.

• Difficulty regulating your blood pressure, which may cause blood clots. 

But it is important to point out that these findings are largely theoretical. Ultimately, more research is needed to know if how much water a person drinks directly impacts their risk of developing a blood clot. 

All that being said, drinking enough water is important for many aspects of your health. And even if it doesn’t prevent blood clots, it will keep your blood flowing and eliminate waste from your body.

Can drinking too much water thin your blood?

Drinking too much water will impact the amount of proteins in your blood that help it form clots. However, it won’t “thin your blood” and prevent you from being able to form blood clots.

Drinking too much water can affect the blood by lowering the concentration of important electrolytes like sodium (salt). Overhydration can lead to a condition known as “hyponatremia,” which means the body doesn’t have enough sodium. This is different from clotting. 

Can dehydration cause blood clots?

If a person is dehydrated enough, this can lead to decreased blood flow. But dehydration alone is unlikely to cause blood clots, especially for people who are otherwise healthy. 

There are several other factors that can increase the likelihood that you develop a blood clot, such as:

• Decreased mobility (for example, bed rest for more than 5 days)

• Older than age 40

• History of previous blood clot

• History of heart attack

• Recent surgery

• Childbirth

And there are many more medical conditions that increase someone’s risk, many of which are outside their control. This is why some people go on medications — called anticoagulants — that decrease their likelihood of developing a blood clot.

What are some other tips to help prevent blood clots?

Even though many risk factors for blood clots can’t be changed, there are still things you can do to help prevent them.

In addition to staying hydrated, you can lower your risk of developing a blood clot when you:

• Stay active: Moving around is one of the easiest and most effective ways to keep your blood flowing. This can be as simple as regular walking breaks during the work day. Or you can park your car a little further from your destination.

• Avoid long stretches of sitting still: This is especially important when you are traveling on a long flight or car ride. If you have to stay sitting, moving your feet back and forth and pumping your legs can help. And even better, standing up and taking a few steps in the aisle throughout the flight can decrease your risk of blood clots too.

• Stop smoking: Smoking cigarettes has been shown to increase a person’s likelihood of developing a blood clot. Smoking damages the lining of blood vessels and makes it easier for blood cells to stick together and form a clot. 

• Wear compression stockings: Compression stockings help decrease the chances that a person develops a blood clot by applying pressure to your ankles and legs. The tightness increases blood flow and prevents blood from pooling and clotting.

Why trust our experts?

Written by:

Cherilyn Davis, MD

Cherilyn Davis, MD, is a board-certified pediatrician in New York City. She has held local and national roles at the American Medical Women’s Association including board member of the physician division and physician chair of social media.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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