Confounding and studies of 'moderate' alcohol consumption: the case of drinking frequency and implications for low-risk drinking guidelines.

AIMS: Many observational studies suggest that increased drinking frequency is associated with reduced mortality among those with low-dose alcohol consumption. The purpose of this paper was to examine whether frequent drinkers consume lower-risk amounts during drinking days or have favorable risk factor profiles compared with those who drink less frequently, and discuss implications for the larger debate about the limitations of non-randomized studies about 'moderate' drinking and the development of low-risk drinking guidelines.
METHODS: Data from the 2008 Behavioral Risk Factor Surveillance System survey were used to characterize alcohol consumption characteristics and their relationship with risk factors among adult drinking men who consumed an average of fewer than two drinks per day and adult drinking adult women who consumed an average of less than one drink per day.
RESULTS: Those who drank relatively infrequently (14 or fewer days per month) consumed more during drinking days, were more likely to exceed the US Dietary Guidelines drinking limits (41.0% versus 9.7%) and had a larger proportion of drinking days that included binge drinking (13.4% versus 4.3%). Infrequent drinkers also had a higher prevalence of 13 of 15 risk factors assessed. Findings from analyses of those aged ≥40 years were similar.
CONCLUSIONS: Among those with low average alcohol consumption, infrequent drinkers drink more during drinking days and have unfavorable risk factors profiles compared with more frequent drinkers, suggesting that confounding may contribute to favorable associations with 'moderate' average alcohol consumption and increased drinking frequency observed in non-randomized studies.