Heavy Drinking Bigger Risk for Stroke in Middle Age Than Hypertension
The new study fills in some details in a relationship previously revealed by other studies. One study, for example, found that risk of spontaneous intracerebral hemorrhage was increased in heavy drinkers and that heavy drinkers with this type of stroke aged under 60 were almost twice as likely to die in the next two years as nondrinkers. Other research has shown that drinking more than two standard alcoholic drinks per day “ages” the brains of men in middle age by about six years.
Drinking and Stroke Risk
The basic aim of the study was to investigate the effect of drinking during midlife on stroke risk, and a large sample of 11,644 participants from the Swedish Twin Registry was used for the study. The researchers specifically looked at those who answered questionnaires between 1967 and 1970 and for whom there was data on alcohol consumption. The focus on twins makes it easier to determine the effect of genetic factors and factors related to early life. All participants in the study were aged 60 or under at the time of the original survey, but the fact that it was conducted so long ago means the researchers had over 40 years’ worth of follow-up data.
They took smoking status, high blood pressure, cardiovascular disorders, diabetes, body mass index (BMI), exercise and other factors into account when analyzing the data. Heavy drinkers were classed as those having over two drinks a day on average, and light drinkers were defined as those having less than half a drink per day on average. The comparison was conducted with light drinkers because many non-drinkers may have stopped due to health problems and may have an increased risk as a result.
Overall, 29 percent of the participants had a stroke over the course of the study. Those classed as heavy drinkers had a 34 percent increase in stroke risk compared to the light drinkers. Those drinking heavily in midlife—in their 50s and 60s—were found to have a stroke five years sooner than light drinkers. This is a particularly important result because stroke risk from high blood pressure doesn’t start increasing until age 75, and for diabetes, it’s age 80. In other words, drinking raises risk much sooner than other relevant factors.
Lead author Pavla Kaldecova commented that “alcohol consumption might be such an important risk factor for younger people (age 50 to 60 years), and this risk is comparable with known factors (diabetes and hypertension) in later age.” She added that, “Shortening time to stroke by five years was quite surprising as well, but we did not possess any assumptions, as no similar analysis had been performed before.”
In fact, the risk of stroke from drinking was greatest when the drinking took place in midlife. When older drinkers were considered (i.e., those 75 and older), the alcohol-related risk was less relevant than the risks conferred by high blood pressure and diabetes.
Finally, the researchers found that in identical twins, the heavy drinkers were more likely to have a stroke than their siblings who drank lightly. This is a strong indication that alcohol was the relevant factor, rather than a genetic susceptibility or factors related to early life environment that both twins would share.
Recommended Limit for Drinking and Stroke Risk
The study is in close agreement with general recommendations about drinking. The American Heart Association recommends a limit of two standard drinks per day for men and one for women, and the study found that stroke risk increases when alcohol is consumed above these gender-specific guideline quantities.
However, there are some apparently contradictory results on moderate drinking, with some showing a general benefit to the cardiovascular system from light to moderate drinking. The reason for this in terms of stroke risk comes down to the type of stroke. For ischemic stroke—caused by blood clots in the brain—light to moderate drinking does appear to have a protective effect, but for hemorrhagic stroke—caused by bleeding in the brain—the risk is significantly increased. The majority of stroke cases in this study were the hemorrhagic variety.
The difference occurs because light to moderate drinking may improve blood flow in the brain, helping minimize the effect of blood clots. However, hemorrhagic stroke involves blood flow being too heavy, potentially explaining the alcohol-related risk for that type of stroke.