Although numerous studies have shown that light to moderate consumption of alcohol may have associated health benefits, a recent study conducted by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) has shown that - among dependent drinkers - alcohol consumption is never protective and likely increases the risk of death.
"Most studies of alcohol consumption and mortality find what we call a ‘J-shaped curve,’" said Deborah A. Dawson, a National Institutes of Health statistician and author of the study. "What this means is that light to moderate drinkers have the lowest risk of mortality - even lower than nondrinkers - and the heaviest drinkers have the highest risk. I thought it would be interesting to see what influence alcohol dependence might have on this association, and we can see that there it eliminates any protective effect of alcohol."
Dawson’s study, the first to examine alcohol dependence and its relation to all causes of mortality, was published in the January edition of Alcoholism: Clinical & Experimental Research. It matched information collected through the 1988 National Health Interview Survey Alcohol Supplement for 37,682 U.S. adults aged 25 years and older with 3,586 deaths listed in the National Death Index from 1988 to 1995. Analysis adjusted for age, gender, race/ethnicity, marital status, education, income, labor force status, body mass index, smoking status, and poor health indicators at baseline. Drinks were averaged across all days: those considered light drinkers consumed about one to three drinks a week; those considered moderate drinkers consumed between three drinks a week and two drinks per day; heavy drinkers consumed between two and four drinks per day; and very heavy drinkers consumed an average of more than four drinks per day. Similar to other studies, light and moderate drinking levels demonstrated protective health effects for nondependent drinkers. Among dependent drinkers, however, these protective benefits were nullified and the risks at heavier drinking levels were intensified.
Alcohol, like many things in life, has both benefits and risks. Scientists like Dawson are wary of pointing out one without noting the other: "I wouldn’t want people to look at these findings and say, ‘well, as long as I’m not dependent, I can drink as much as I want,’" she said. "It’s important to point out that when you become a very heavy drinker, you’ve got almost a 50/50 chance of becoming dependent. And once you become dependent, you will experience a very significantly increased risk of death."
Other studies have found that health risks associated with heavy drinking include cirrhosis of the liver, certain types of cancer, and violence- and accident-related trauma. Yet even before a potential shift to heavier drinking may occur, there are a number of risks associated with moderate drinking. These include strokes caused by bleeding (as opposed to strokes caused by blocked blood vessels, which seem to be mediated by moderate alcohol consumption), motor vehicle and other accidents caused by impaired thinking and skills, interactions with medications, some cancers, and potential birth defects.
Nonetheless, it seems apparent that light and moderate consumption of alcohol are associated with protective health effects. Scientists, however, are stumped as to exactly why that is. It could be that alcohol itself causes lower health risks, or it could be that other factors associated with light and moderate drinking - such as lifestyle, diet, exercise, and type of alcoholic beverages - play a role.
"I’m firmly convinced that the shape of the mortality curve," said Mary C. Dufour, Deputy Director of NIAAA, "is primarily driven by the fact that heart disease is the leading cause of death, and stroke is third." Heart attacks and other forms of coronary heart disease (CHD) result in approximately 500,000 deaths per year, or about 25 percent of the nation’s total mortality. Research has shown that moderate drinking is associated with a lower CHD risk than either heavy drinking or abstention.
"There are also studies that show that light and moderate drinkers are different people than abstainers and heavy drinkers," Dufour continued. "They’re more likely to exercise and be at their ideal body weight, more likely to get eight hours of sleep at night, and more likely to eat a balanced diet." In addition, as noted in the October 1999 issue of Alcohol Alert, choice of beverage may play a role: drinkers who prefer wine tend to smoke less, drink less, and have a more healthful diet than those who prefer beer or liquor. In other words, health-related lifestyle factors that are consistently associated with drinking levels could play a large role in determining overall health risks.
Dawson says researchers had suspected her study’s findings but, until now, did not have evidence to support those suspicions. "There are a lot of substantive issues related to this study," she said. "One of its more important findings is that, yes, it’s probably safe to drink in moderation but don’t carry it so far that you run the risk of becoming dependent."