Can coffee cause high hematocrit? Exploring the connection

November 21, 2025 •

5 min read

Did you know a recent 2024 study found that controlled coffee intake in healthy young adults was associated with a modest increase in hematocrit? This intriguing finding raises the question: can coffee cause high hematocrit, or are there other more significant factors at play?

Quick Summary

Recent research suggests controlled coffee intake may modestly increase hematocrit levels by influencing red blood cell characteristics, but dehydration is a more common factor impacting readings.

Key Points

Modest Increase, Not Primary Cause: Some studies show a modest, but statistically significant, increase in hematocrit with controlled coffee intake, but it is not considered a primary cause of clinically significant erythrocytosis.
Complex Mechanisms: The effect of coffee on hematocrit is complex, involving potential influences on red blood cell production and function, rather than a simple cause-and-effect relationship.
Dehydration is a Key Factor: Coffee's diuretic properties can cause dehydration, leading to an artificially high hematocrit reading through hemoconcentration, a more likely scenario than overproduction of red blood cells.
Primary Causes are Medical: Serious high hematocrit (polycythemia) is far more likely caused by underlying medical conditions, such as chronic lung or heart disease, or rare bone marrow disorders.
Lifestyle and Environmental Factors: Smoking, living at high altitude, and using testosterone therapy are also more significant contributors to elevated hematocrit than coffee consumption.
Consult a Doctor: For genuinely high hematocrit readings, it is essential to consult a healthcare provider to determine the root cause, as it's unlikely to be solely from coffee.

Understanding Hematocrit and Erythrocytosis

Hematocrit (Hct) is the measurement of the percentage of red blood cells (RBCs) in your total blood volume. RBCs are essential for delivering oxygen from the lungs to all the tissues in the body. An Hct test is a standard part of a complete blood count (CBC) and is used to screen for or monitor blood-related conditions. A high hematocrit, a condition known as erythrocytosis, means you have a higher than normal proportion of red blood cells. This can make the blood thicker and increase the risk of blood clots, heart attack, and stroke. While alarming, a high reading doesn't always signal a serious illness, as several factors can influence the results, including lifestyle choices and hydration levels.

The Nuanced Relationship Between Coffee and Red Blood Cells

For most people, coffee is not a direct cause of a clinically significant high hematocrit. The relationship is complex and influenced by several mechanisms, some of which may lead to a modest increase while others suggest a potential decrease.

The Direct Effect of Coffee on Erythrocytes

Some of the most direct evidence comes from a 2024 study on healthy young adults. Participants who drank a controlled amount of filtered coffee for three weeks showed a statistically significant, albeit modest, increase in both erythrocyte count and hematocrit value. The study authors propose a few potential mechanisms for this finding:

Influence on Erythropoiesis: Caffeine, as an adenosine receptor antagonist, may interfere with adenosine signaling, which is known to inhibit erythropoiesis (the production of red blood cells). By counteracting this inhibition, caffeine could potentially lead to an increased erythrocyte count.
Enhanced Antioxidant Capacity: Coffee is rich in antioxidants. Some research indicates that coffee intake can improve the antioxidant capacity of red blood cells, potentially enhancing their function and survival, which could contribute to a higher count.
Improved Erythrocyte Deformability: The 2024 study also noted that coffee consumption led to an improvement in red blood cell deformability, meaning the cells were better able to change shape to navigate the circulatory system. This is a beneficial effect for microcirculation.

The Dehydration Effect and Hemoconcentration

One of the most common and immediate ways coffee can influence a hematocrit reading is through its diuretic effect, meaning it can cause the body to excrete more fluid. Dehydration, or a low level of fluid in the blood (plasma), is a well-known cause of temporarily high hematocrit. This is because without sufficient plasma volume, the percentage of red blood cells in the remaining blood sample is artificially concentrated. This phenomenon, called hemoconcentration, does not mean the body is producing more red blood cells but rather that the ratio of cells to plasma has changed. Rehydrating properly can quickly resolve this type of elevated reading.

The Iron Absorption Factor

On the other hand, heavy coffee consumption, especially when ingested with meals, can actually reduce iron absorption. This is primarily due to the polyphenols and tannins present in coffee. Since iron is a vital component for producing hemoglobin, which is carried by red blood cells, long-term high coffee intake could potentially contribute to iron deficiency and, consequently, lower red blood cell parameters, including hematocrit. This is particularly relevant for individuals with an existing risk of iron deficiency, such as women of childbearing age.

Comparison: Coffee Consumption vs. Underlying Medical Conditions

To put coffee's effect into proper perspective, it is crucial to compare its influence against more significant medical causes of erythrocytosis. The table below outlines the key differences.


Aspect	Coffee Consumption	Underlying Medical Conditions
Magnitude of Effect	Generally minor and modest; a small change in percentage points.	Can cause significantly high hematocrit levels requiring medical intervention.
Mechanism	Complex; potentially involves enhancing RBC function, influencing erythropoiesis, or causing temporary hemoconcentration via dehydration.	Involves major physiological responses, such as chronic hypoxia, or bone marrow disorders leading to overproduction.
Duration of Effect	Transient; high readings due to dehydration are quickly resolved with proper hydration.	Often chronic and persistent, requiring ongoing medical management or treatment.
Risk Profile	For most healthy people, the risk is minimal. Excessive intake carries other health risks unrelated to erythrocytosis.	High risk, including increased chance of blood clots, stroke, and heart attack if left untreated.

Other Primary Causes of High Hematocrit

If you have a high hematocrit reading, it is far more likely to be caused by one of these factors than by your morning cup of joe.

Dehydration: As mentioned, this is the most common and benign cause. It's the first thing a doctor will check for, especially if no other symptoms are present.
High Altitude: Individuals who live at high altitudes naturally have a higher hematocrit. This is a physiological adaptation to compensate for lower oxygen levels in the air.
Smoking: The carbon monoxide in cigarette smoke reduces the amount of oxygen that can be carried by red blood cells. To compensate, the body produces more RBCs, increasing the hematocrit.
Chronic Obstructive Pulmonary Disease (COPD): This and other chronic lung diseases lead to low blood oxygen levels (hypoxia), stimulating the bone marrow to produce more red blood cells.
Congenital Heart Disease or Heart Failure: Poor heart function can result in insufficient oxygen transport, prompting the body to increase red blood cell production.
Polycythemia Vera: This is a rare myeloproliferative disorder where the bone marrow produces an excessive number of red blood cells, and it is a serious medical condition.
Testosterone Therapy: Using testosterone supplements can increase red blood cell production and lead to elevated hematocrit levels.

Conclusion: Can coffee cause high hematocrit?

While some research shows a modest and statistically significant increase in hematocrit associated with controlled coffee intake in specific populations, it's a minor effect and not a primary cause of concern for clinically high hematocrit. The relationship is more complex, involving both potential minor stimulatory effects and inhibiting factors like reduced iron absorption. The most direct connection between coffee and a high hematocrit reading is its diuretic property causing dehydration and hemoconcentration, which is easily rectified by proper hydration. For most individuals, genuinely high hematocrit is a sign of a more serious underlying medical condition, not a casual effect of their daily caffeine intake. If you have concerns about your hematocrit levels, it is always best to consult a healthcare professional to rule out more significant medical issues. You can learn more about general health and the hematocrit test from MedlinePlus.

Frequently Asked Questions

Excessive coffee intake, particularly if it leads to dehydration due to its diuretic properties, can cause a temporary, artificially high hematocrit reading. This is due to hemoconcentration, where the percentage of red blood cells appears higher because of reduced blood plasma volume, not due to an overproduction of red blood cells.

The main causes of clinically high hematocrit (erythrocytosis) are medical conditions and environmental factors like chronic lung disease, heart failure, polycythemia vera, smoking, and living at high altitudes, which induce the body to produce more red blood cells.

Research is mixed and complex. Some studies suggest coffee may enhance antioxidant capacity and improve red blood cell deformability, while other research on blood donations indicates that high caffeine levels may negatively impact red blood cell storage quality and transfusion effectiveness.

Decaffeinated coffee is less likely to cause a high hematocrit reading due to dehydration since it contains minimal caffeine. However, other compounds in coffee can still influence blood components, though any effect on hematocrit would likely be minor and inconsistent.

While temporary dehydration is not usually a major concern, severe or chronic dehydration is unhealthy. A persistently high hematocrit, regardless of the cause, increases the risk of blood clots. It is crucial to address the root cause, whether simple dehydration or a more serious medical issue.

The most effective natural method is staying well-hydrated throughout the day, especially if dehydration is the cause. Lifestyle factors like avoiding smoking, engaging in moderate exercise, and limiting alcohol can also help. Always consult a doctor for personalized advice before making significant changes.

It is best to consult your doctor for medical advice. If your high hematocrit is caused by an underlying medical condition, stopping coffee may not be the primary solution. However, ensuring you are not dehydrated by drinking plenty of water in addition to or instead of coffee is a good practice.