Does Alcohol Thin Your Blood?

Even Moderate Amounts Can Thin Blood

Mature woman at desk reading book by glass of red wine
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Moderate drinking is a two-edged sword. It may have some beneficial effects, but at the same time, those very same effects could be negative in other areas of your health.

Moderate drinking is also a balancing act, of sorts. If you drink exactly the right amount to be "moderate" it may be better in some health effects than not drinking at all, but if you drink just a tad over the guidelines for moderate, it is much more dangerous than not drinking at all.

It's called the J-curve.

Take blood coagulation, for example. If you drink a moderate amount of alcohol - defined in one large study as three to six drinks per week - it may have the benefit of acting as a blood thinner and be protective against clotting in clogged arteries, like aspirin does.

At the same time, thinning the blood can hasten bleeding from injured arteries, increasing the risk of bleeding strokes.

Lower Rates of Heart Disease, More Strokes

Some studies have shown that moderate drinkers tend to have lower rates of heart disease, but higher rates of bleeding-type strokes than abstainers.

However, some researchers believe that the ability of moderate drinking to make blood platelets less "sticky" may mediate the negative effects of moderate drinking.

A study at the Beth Israel Deaconess Medical Center confirms that moderate drinking has effects on blood coagulation – primarily as a "blood thinner" – which can have both positive and negative effects.

Contrasting Effects of Alcohol

"The contrasting effects of alcohol are similar to the effects of blood thinners like aspirin, which clearly prevent heart attacks but at the expense of some additional bleeding strokes," said Kenneth J. Mukamal, corresponding author for the study. "Acting as a blood thinner makes sense, because heart attacks are caused by blood clots that form in clogged arteries, and blood thinners can hasten bleeding from injured arteries.

Based on these findings, we speculated that moderate drinking would also act as a blood thinner."

Mukamal said previous research had shown that moderate drinkers tend to have "less sticky" platelets than abstainers, meaning that fewer blood elements cluster to form blood clots.

'Sticky' Platelets Can Be Dangerous

"Yet no one before had looked at whether alcohol affects how easily platelets are activated," he said. "This is important because activated platelets are much stickier than normal ones."

In 1971, a total of 5,124 men and women enrolled in the Framingham Offspring Study of risk factors for cardiovascular disease – the sons and daughters of participants in the original Framingham Heart Study. Participants have been examined and interviewed every four years since 1971, except for an eight-year interval between the first and second visits.

Potential Blood Thinner

This study uses data collected from 3,798 of those participants, examined between April 1, 1991 and March 1, 1994 (the fifth examination cycle), eventually analyzing data provided by a total of 1,037 participants (460 men and 577 women) for platelet activation and 2,013 participants (879 men and 1,134 women) for platelet aggregation.

"We found that among both men and women, an intake of three to six drinks per week or more was linked to lower levels of stickiness measured by aggregability," said Mukamal. "Among the men, we also found that alcohol intake was linked to lower levels of platelet activation. Together, these findings identify moderate drinking as a potential blood thinner."

Mukamal believes that the minor differences found between the men and women were more likely due to statistical issues than to any clear gender differences.

Risk Factors for Vascular Disease

Mukamal said the next step is to evaluate these findings in other populations.

"Heart attacks far outnumber bleeding-type strokes in the United States," he said, "but in some countries such as Japan, they have much higher rates of bleeding strokes and lower rates of heart attacks than we do, which is perhaps related to dietary differences."

No Reason to Start Drinking

"Our findings add to a large body of evidence showing that moderate drinking has effects on blood coagulation, which may have both good and bad effects, but now identify a new avenue by which this effect may occur," said Mukamal. "By themselves, these findings have more importance for understanding risk factors for vascular disease than any clinical relevance, and should not be used by people as any reason to begin drinking."

The bottom line is, although moderate drinking may have some health benefits, there is risk involved too. If you don't drink, the risks of developing other problems associated with alcohol may be too great to begin drinking for its limited benefits.


Mukamal, KJ, et al. "Alcohol Consumption and Platelet Activation and Aggregation Among Women and Men: The Framingham Offspring Study." Alcoholism: Clinical & Experimental Research October 2005

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