“Just two alcoholic drinks a day is enough to significantly increase the risk of high blood pressure and heart disease,”_ The Daily Telegraph_ reported. The newspaper went on to describe a study which found that women who regularly have two alcoholic drinks, and men who have three, run an increased risk of developing metabolic syndrome. People are classified as having this condition if they have multiple risk factors, such as high cholesterol, high blood pressure and problems controlling blood sugar levels in the body. Together they can be an early warning sign of future health problems.
More than half of the 1,500 people in this US study drank more than the current guideline limits. At least one sign of metabolic syndrome was present in 72% of men and 68% of women, while one in five had already developed it. The researchers found that the risk of metabolic syndrome in those people who drank more than the US guidelines increased by 56%. This study cannot prove that regular alcohol intake causes the syndrome, and other research indicates that any association is more complex than that. However, the findings are still supportive of keeping to the recommended amounts.
Where did the story come from?
Dr Amy Fan and colleagues, mainly from the National Center for Chronic Disease Prevention and Health Promotion in Atlanta, carried out the research. Sources of funding are not mentioned in the article, which was published online in the peer-reviewed medical journal The Journal of Clinical Endocrinology and Metabolism.
What kind of scientific study was this?
This was a cross-sectional analysis of data from the large National Health and Nutrition Examination Survey, carried out in the US between 1999 and 2002. The researchers were interested in the relationship between different aspects of alcohol consumption and metabolic syndrome. They state that there is conflicting evidence about how much alcohol intake is associated with an increased rate of metabolic syndrome, with an increased rate in some studies and a lower rate in others.
Using the survey database, current drinkers (those who drank more than 12 alcoholic drinks in 12 months) who were between the ages of 20 and 84 and who did not have cardiovascular disease, were selected. Those who did not have enough details to allow a diagnosis of metabolic syndrome were excluded, as were those who were pregnant or had been told to moderate their drinking by a doctor. This gave the researchers 1,529 people for the analysis.
There are several possible definitions of metabolic syndrome, and the researchers chose to use the National Cholesterol Education Program’s definition. This defines the syndrome as a constellation of risk factors, where a person must have at least three of the following: impaired levels of fasting glucose (6 mmol/L or more) or diabetes mellitus, high triglycerides (a type of fat) in the blood, abdominal obesity, high blood pressure, or low high-density-lipoprotein or “good”, cholesterol. In addition to dividing people into those with or without the condition, the researchers created a scale based on whether the participants had 0, 1, 2 or 3 of the metabolic abnormalities listed.
Data about alcohol consumption had been collected by a questionnaire, which asked how often drinks were consumed. An example of a question is: “On those days when you drank alcoholic beverages, on average, how many drinks did you have?” This allowed researchers to group the responses into people who drank one, two, or more than three drinks per day on days they were drinking. US guidelines suggest that men who usually consume three or more drinks a day and women who usually consume two or more drinks a day are drinking in excess. Binge drinking in three categories (“none, once a week or more than once a week”), was assessed by asking the “number of days you had five or more drinks in the past 12 months”.
Complex statistical modelling was used to assess the associations between all the factors recorded. It took into account things such as age, sex, ethnicity, years of education, family history of coronary heart disease, stroke, diabetes, diet, smoking, physical activity and how long they spent in sedentary behaviour such as watching television.
What were the results of the study?
The researchers reported that metabolic syndrome was associated with daily consumption of alcohol exceeding what was recommended by US Dietary Guidelines, which is two or more drinks per drinking day for women, three or more drinks per drinking day for men, and binge drinking once or more a week.
The association was described numerically, using the odds ratio (OR). The OR is the chance that someone will have metabolic syndrome when their drinking exceeds the recommended guidlelines, compared to the odds of someone having the syndrome when they did not exceed the recommended amounts. The OR was 1.56, which suggests a 56% increase in the odds of having metabolic syndrome in people who drink above the recommended amount (95% confidence interval 1.02 to 2.40). This increase was statistically significant. The OR for metabolic syndrome if they were binge drinking once or more a week was 1.84 although this increase was not statistically significant (95% CI 0.96 to3.50), .
The researchers found similar results when they looked at the link between alcohol consumption and the number of individual metabolic abnormalities a person had. In these analyses, exceeding the recommended alcohol consumption and binge drinking both increased the risk of having a greater number of metabolic abnormalities.
What interpretations did the researchers draw from these results?
The researchers concluded that “public health messages should emphasise the potential cardiometabolic risk associated with drinking in excess of national guidelines and binge drinking”.
What does the NHS Knowledge Service make of this study?
This study demonstrates the importance of alcohol consumption patterns as predictors of health. Some limitations were recognised by the authors:
- This was a cross-sectional study, and with this type of study design it is not possible to say that one thing causes another, in this case whether alcohol causes metabolic syndrome. The association found in this study, though supportive of this idea, should be seen in the context of other studies on the subject. These show sufficient conflicts, i.e. opposing results, to suggest that the association is not a simple one.
- The statistical adjustments that the researchers used may not be sufficient to rule out confounding by imperfectly measured, unmeasured or unknown variables. As with many studies of this type, there are socioeconomic factors which may be associated with both drinking and having other cardiovascular risk factors, and these may not have been completely accounted for.
- Interestingly, the researchers claim that by excluding the non-drinkers from their study they have avoided some of the statistical problems that can occur because of the variation in type of “non-drinker”. Other studies of this type have found that this group often includes former drinkers, lifelong abstainers, and irregular abstainers. The authors argue that this might explain why previous studies have shown moderate drinking to be linked with better health outcomes than non-drinking.
Metabolic syndrome consists of several risk factors which, individually, are known to increase the risk of heart disease and stroke. The possibility that alcohol may increase the chance of this syndrome is another reason for people to heed advice to moderate their intake. However, it is the evidence for a direct link with heart disease which deserves more study and which could aid attempts to define a “safe” alcohol threshold.
Sir Muir Gray adds...
Three glasses a day? I could not cope. Eat less and drink less is the best advice for adults.