How does alcohol affect stroke risk? Study investigates

As the winter holidays are fast approaching, alcohol consumption rates are about to go up. While low to moderate drinking has been shown by some studies to have beneficial effects on the heart and circulatory system, new research suggests alcohol use may increase the risk of some types of stroke and not others.

Most people have consumed alcohol at some point in their lives. Low to moderate levels of alcohol consumption have been shown to be good for one's health, but high and heavy drinking can have serious negative consequences.

Now that Thanksgiving is here, it is important to remind ourselves of the dangers of seasonal binge drinking. The National Institute on Alcohol Abuse and Alcoholism (NIAAA) warn about the myths around alcohol use and give advice on how to drink safely during the holidays.

Up to one drink per day for women and two drinks per day for men counts as moderate drinking. According to the NIAAA, moderate drinking seems to lower the risk of heart disease, ischemic stroke, and diabetes.

However, consuming alcohol in high amounts remains highly dangerous. A large number of Americans die of alcohol-related incidents every year, making alcohol the fourth leading preventable cause of death in the United States.

New research looks at the impact of alcohol on the risk of developing stroke.

Analyzing the link between alcohol and stroke

Researchers from the Karolinska Institute in Sweden and the University of Cambridge in the United Kingdom examined associations between alcohol consumption and different types of stroke.

The study consisted of a systematic review and meta-analysis of existing studies. Researchers looked at 25 prospective studies containing data on ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage.

Studies included data from The Cohort of Swedish Men and the Swedish Mammography Cohort, summing up a total of 18,289 ischemic stroke cases, 2,299 intracerebral hemorrhage cases, and 1,164 cases of subarachnoid hemorrhage.

Levels of alcohol consumption were evaluated using patients' self-reporting. Participants answered a series of questions using a questionnaire or an interview.

Using standardized measures of alcohol, alcohol consumption was divided into four categories: light drinking (one daily drink or less), moderate drinking (one to two drinks per day), high drinking (two to four drinks per day), and heavy drinking (more than four drinks daily).

The study adjusted for variables such as age, sex, smoking, body mass index (BMI), and diabetes.

Results were published in the open-access journal BMC Medicine.

Alcohol may increase the risk of hemorrhagic stroke

The meta-analysis looked at two different types of stroke: ischemic and hemorrhagic.

Ischemic stroke is the most common type of stroke. It is caused by a blood clot blocking the flow of blood and oxygen from reaching the brain.

A hemorrhagic stroke occurs either when an aneurysm bursts, or a weakened blood vessel leaks. The result is bleeding either inside the brain, causing an intracerebral hemorrhage, or, less commonly, bleeding between the brain and the tissue covering it, causing a so-called subarachnoid hemorrhage.

The study revealed that light and moderate alcohol consumption seemed to lower the risk of ischemic stroke, but it had no impact on the risk of developing hemorrhagic stroke.

Dr. Susanna Larsson, lead author of the study, explains why this may be:

"Previous research has found an association between alcohol consumption and lower levels of fibrinogen - a protein in the body which helps the formation of blood clots. This may explain the association between light to moderate alcohol consumption and lower ischemic stroke risk."

However, drinking may, in fact, increase the risk of hemorrhagic stroke. This is more apparent when looking at the heavy drinking category.

"Our results showed that heavy drinkers were about 1.6 times more likely to suffer from intracerebral hemorrhage and 1.8 times more likely to suffer from subarachnoid hemorrhage. The association between heavy alcohol consumption and these two types of stroke was stronger than that for ischemic stroke."

Dr. Susanna Larsson

Therefore, even if moderate drinking may have a beneficial effect by lowering the risk of ischemic stroke, the disadvantages might outweigh the benefits.

"The adverse effect of alcohol consumption on blood pressure - a major risk factor for stroke - may increase the risk of hemorrhagic stroke and outweigh any potential benefit," Dr. Larsson mentions.

Strengths and limitations of the study

Dr. Larsson points out that the large sample size included in the analysis allowed for accurate associations between a wide range of alcohol consumption patterns and patient subgroups.

"This is the first study that combines the results from all available prospective studies on alcohol consumption and risk of hemorrhagic stroke subtypes," Dr. Larsson says.

However, some of the studies included in the meta-analysis were small in sample size, which means that the positive effects of light to moderate alcohol use may have been overestimated.

Also, the meta-analysis could not use the same categories of alcohol consumption across all the studies, as the authors lacked individual patient data.

Finally, as this is an observational study, it cannot show causality between using alcohol and the risk of developing different kinds of stroke.

Learn how moderate drinking can benefit 'good' cholesterol levels.