Moderate drinking has effects on blood coagulation, primarily as a "blood thinner"

Population studies have shown that moderate drinkers tend to have lower rates of heart disease but higher rates of bleeding-type strokes than abstainers. A potential mediator of these two contrasting effects of alcohol may be platelet function.

A study in the October issue of Alcoholism: Clinical & Experimental Research confirms that moderate drinking has effects on blood coagulation - primarily as a "blood thinner" - which can have both positive and negative effects.

"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, an internist at Beth Israel Deaconess Medical Center and 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 added that 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. "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. 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 added that the minor differences found between the men and women were more likely due to statistical issues than to any clear gender differences.

"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 next step for Mukamal and his colleagues 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."

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