(CNN) - There's an increased risk of dying from heart disease if you drink frequently -- especially if you are in the lowest socioeconomic class, according to a study published Tuesday in the journal PLOS Medicine.
By comparison, the negative effects of binge drinking are more equitable. No matter your socioeconomic status, weekly binge drinking raises your risk of dying from heart disease in comparison with those who don't binge, the researchers estimated.
"Although a number of previous studies have found a 'protective effect' of moderate alcohol consumption, according to results from our study, this seems to be mostly the case among people with more advantaged socioeconomic position," said Dr. Øyvind Næss, senior author of the study and a senior scientist at the Norwegian Institute of Public Health. "This 'protective effect' is almost absent among the disadvantaged."
The French paradox
The relationship between moderate drinking and heart disease was noticed decades ago as part of "the French paradox."
As explained by Dr. Michael Goyfman, director of clinical cardiology at Northwell Health's Long Island Jewish Forest Hills in New York, the paradox is this: The French tend to eat the kinds of fatty foods that lead to heart problems, yet cardiovascular disease is less common in France than expected.
Scientists hypothesized that this is because the French also tend to drink red wine with their meals, said Goyfman, who was not involved in the new study.
"Over the years, they've done numerous studies where they ultimately did show that red wine consumption and other types of alcohol seemed to decrease the risk of having cardiovascular disease," he said.
The "novel part" of the new study, Goyfman noted, is that Næss and his co-researchers not only looked at the health effects of alcohol, they stratified effects based on socioeconomic status.
What's with the glass, not what's in it
Gathering socioeconomic and health data from the Norwegian Institute of Public Health in Oslo, a team of international researchers analyzed information on 207,394 adults who completed their census questions between the years 1960 and 1990. Each person's socioeconomic position was classified as either high, middle or low, based on 20 indicators, including household income and education.
During the study period, there were a total of 8,435 deaths due to cardiovascular disease.
Infrequent drinking was associated with a lower risk of death due to cardiovascular disease, the researchers found.
The researchers defined infrequent consumption as between once a month and once a week. Moderately frequent drinking was defined as two to three times per week, and very frequent was four to seven times per week.
Very frequent drinking was associated with increased risk of cardiovascular death -- but only among those with low socioeconomic position, the researchers found. As a group, participants of low socioeconomic status who drank frequently experienced about 42% more deaths due to cardiovascular disease than infrequent drinkers, the study authors estimated.
The team also found that moderately frequent drinkers had a lower risk of dying from cardiovascular disease than infrequent drinkers: Overall, moderately frequent drinkers experienced about 22% less deaths due to heart disease, according to the study estimates.
This beneficial relationship was slightly more pronounced among moderately frequent drinkers of high socioeconomic position, the researchers said. Moderately frequent drinkers of high class experienced about 33% less deaths than infrequent drinkers, based on the team's estimates.
This finding "suggests that the proposed benefit from drinking a glass of wine per day could actually be the lifestyle that accompanies the glass -- and not the contents (of the glass) in itself," said Eirik Degerud, co-author of the study and a postdoctoral fellow at the Norwegian Institute of Public Health.
Five or more drinks on the same occasion was considered a binge. (In the United States, five or more drinks is considered a binge for men. For women, the standard is four or more drinks.) When responding to how often they binged, participants' answers included "not last year," "a few times (in a year)," "one to three times a month" and "once a week."
Weekly (or more frequent) binge drinkers experienced about 58% more deaths due to heart disease than non-bingers, the researchers estimated.
Binge drinking was equally prevalent among people of all socioeconomic classes, Degerud noted.
"The most important finding was that binge drinking increased the risk of cardiovascular and all-cause mortality in participants with both high and low socioeconomic position," he said.
Goyfman agrees that the new study results are "important."
Effects based on 'social environment'
"One thing to keep in mind is, this study is only based on an analysis of data from a questionnaire," Goyfman said. The study cannot prove causality; you cannot say that "just being in the low socioeconomic status category itself is what causes this less beneficial effect."
Maybe people in a higher socioeconomic status have more time to exercise, or maybe they buy higher-quality and healthier food. Still, the study may be used as a springboard to "delve into this topic further," Goyfman said.
Christina Mair, an assistant professor of behavioral and community health sciences at the University of Pittsburgh, also hopes the study inspires more research.
Mair, who was not involved in the study, believes it has a "key strength" in its "large, population-based database."
The greater impact of drinking on lower socioeconomic status individuals is "an important health disparity to measure, understand and seek to reduce," Mair said. But because of differences in socioeconomic status between Norway and the United States, she noted, the "results may not be applicable here."
"Much of my work focuses on the social environmental determinants of these disparities," Mair explained. For example, she has studied the ways in which lower-income neighborhoods are more socially disorganized and have less access to health-protecting resources, including healthy foods, while having a greater number of liquor stores, which are linked to violence.
"Without addressing disparate environmental conditions and access to resources, we will not be able to eliminate these avoidable disparities," she said.
According to the study authors, the differences in risk across socioeconomic classes could have been influenced by unknown factors, such as whether drinking is accompanied by a different set of behaviors in each class. For instance, those of higher socioeconomic status may be more likely to eat a healthy meal while drinking.
Still, previous studies have shown that people of lower socioeconomic status have higher risk of many unfavorable health outcomes when drinking, Degerud noted: "The risk of hospitalization for alcohol-related events, such as violence or accidents, seem to be higher among those with lower socioeconomic position."
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