The main finding of our study is that light to moderate drinkers of alcohol have better LAF than alcohol abstainers. Although this difference is modest in absolute magnitude, the p values, the consistency in stratified subgroup analyses, and the independence from strictly defined baseline illness make a chance difference unlikely. However, because these data are cross-sectional, interpretation of better LAF as a possible causal benefit of alcohol drinking requires great caution.
One important problem of alcohol categorization relevant to this study, known as the “sick quitter” hypothesis,18
is present in analyses that use all nondrinkers as the referent group. Such categorization fails to separate ex-drinkers from lifelong abstainers. Because ex-drinkers include some who quit drinking because of alcohol-related or other medical problems, this could increase the likelihood of illness among the non-drinker category and make light to moderate drinkers spuriously appear healthier. This issue has been raised for observational studies that show less coronary artery disease risk among light to moderate drinkers than among abstainers.18
Although the alcohol-coronary instance is refuted by studies that use lifelong abstainers as the referent,19
alcohol data for the present analysis of LAF does not enable such direct refutation.
… light to moderate drinkers of alcohol have better lung airway flow than alcohol abstainers.
We attempted to deal with the “sick quitter” problem by studying the subcohort with no evidence of CR disease. A caveat is that because many healthy persons have nonspecific CR symptoms, a proportion of persons in the CR “yes” group were probably free of actual CR disease. In creating this CR composite, we intended to be inclusive in order to derive a group truly free of CR disease. We reason that the “no CR” group, with negative responses to all queries, was unlikely to have quit drinking because of cardiovascular or lung disease. Thus, the better LAF in light to moderate drinkers in this subgroup adds substantial credibility to a possible lung function benefit of light drinking.
The broadness of the category of two or fewer drinks per day precludes ascertainment of a possible threshold. These persons composed more than half of study participants, and, even assuming truthful reporting, include a range from occasional drinking (less than one drink per month) to intake of two large drinks daily. Furthermore, the group almost surely includes heavier drinkers who underreport. By inclusion of some heavy drinkers as “light to moderate” drinkers, underreporting, in a situation where light but not heavy drinking has a possible benefit, diminishes the apparent benefit. In this connection, the decreased prevalence of impaired LAF among those reporting having three to five drinks per day strengthens the validity of our main finding.
These measurements were performed with equipment that was technically inferior to more modern lung-testing machines. Thus, technical factors might be partially responsible for the relatively low FEV1 and FVC numbers we obtained (). However, the implausibility of a systematic relation of technical test aspects to alcohol drinking habits leaves these data valid for the analyses we did.
/FVC ratio is widely used as a screen for COPD. Because COPD is primarily a disease of smokers, the strong relationship between smoking and drinking20,21
makes it difficult to eliminate confounding when analyzing the possible role of alcohol in this condition. Thus, the lesser likelihood of a low FEV1
/FVC among never-smokers in our data () indicates independence of the finding from confounding by smoking.
A few reports have suggested a possible benefit by light to moderate alcohol intake for COPD. A retrospective autopsy study among male veterans showed an inverse relationship of alcohol consumption to emphysema.22
The Lung Health Study in 5887 Canadian smokers with airways obstruction23
found a significant protective effect of moderate drinking in men, but not women, for both hospitalizations and deaths. A 20-year mortality study among 2953 middle-aged men from several European countries24
showed a U-shaped relation between alcohol and COPD mortality.
Speculative mechanisms of potential benefit for LAF by moderate alcohol drinking include anti-inflammatory effects,22
improved mucociliary clearance,1,25
and antioxidant effects.12
Antioxidants in alcoholic beverages are most plentiful as nonalcohol phenolics, especially in red wine.26,27
A report of possible specific benefit for LAF by wine drinking12
found slightly more benefit for white than for red wine. We have no data in our study cohort about beverage choice.
Although benefit by alcohol is one possible explanation for our data, the numerous well-established harmful effects of heavy drinking include impaired lung defenses,1,28,29
with resultant increased susceptibility to infections. This disparity between the possible effects of moderate and heavy drinking must be kept in mind when considering advice to individuals or the general public.