OBJECTIVE: Several, but not all studies, have shown a dose-dependent inverse association with alcohol consumption and rheumatoid arthritis (RA), whereas smoking is an established risk factor for RA. We aimed to study the association between alcohol consumption and RA incidence and investigate a potential interaction between alcohol and smoking habits, regarding RA incidence.
METHODS: We used a prospective cohort study, based on 41 068 participants with detailed assessment of alcohol intake, smoking and potential confounders at baseline in 1997. We ascertained a total of 577 incident cases of RA during a mean of 17.7 years of follow-up through linkage to nationwide and essentially complete databases. Multivariate Cox proportional hazards models were used to estimate HR with 95% CI. Interaction on the additive scale between alcohol and smoking was estimated by calculating the attributable proportion due to interaction (AP).
RESULTS: Overall, alcohol consumption was associated with a 30% reduced incidence of RA (HR 0.69, 95% CI 0.55 to 0.86) with a dose-response relationship (p value for trend <0.001) which remained significant after stratification by age and smoking habits. The positive association between smoking and RA incidence was reduced with increasing alcohol consumption (p value for trend <0.001). A synergistic effect was observed between alcohol and smoking (AP 0.40, 95% CI 0.15 to 0.64), indicating that 40% of the cases among the double exposed are due to the interaction per se.
CONCLUSIONS: Our findings suggest an inverse association between alcohol consumption and RA incidence, and a synergistic effect between alcohol and smoking.
PURPOSE: This paper aims to evaluate the use of Mendelian randomization (MR) analyses for judging the effects of alcohol consumption on the risk of coronary heart disease (CHD).
DESIGN/METHODOLOGY/APPROACH/ This paper presents a review of methodology for MR and describes its early application to judging health effects of alcohol, current uses and a recommended approach of combining MR results with those from observational and experimental studies.
FINDINGS: Early applications of MR to health effects of alcohol consumption were inadequate for providing unbiased results, but newer attempts using polygenic scores show promise. It is important to combine data from MR analyses with those from observational and experimental studies to obtain an unbiased and scientifically sound estimate of alcohol’s effects on health.
PRACTICAL IMPLICATIONS: Giving advice to the public regarding alcohol consumption must be based on accurate, unbiased scientific data; this paper describes attempts to use MR for achieving this goal.
SOCIAL IMPLICATIONS: Given that light-to-moderate alcohol intake is associated with a lower risk of CHD, type II diabetes mellitus and total mortality, it is important to be able to evaluate both the benefits and harms from alcohol before giving advice regarding drinking.
ORIGINALITY/VALUE: This is part of a group of three papers dealing with the potential health benefits and harms associated with alcohol consumption.