Coffee or tea consumption and the risk of rheumatoid arthritis: a meta-analysis

Meta-analysis of the cohort studies revealed a trend of an association between total coffee intake and RA incidence (RR of the highest vs. the lowest group = 1.309, 95 % confidence interval [CI] = 0.967-1.771, p = 0.085). Meta-analysis of case-control studies showed a significant association between total coffee intake and RA incidence (RR = 1.201, 95 % CI =1.058-1.361, p = 0.005). There were differences in the reference groups (all categories of coffee) between the case-control meta-analysis that showed a significant association and the cohort studies where meta-analysis results were non-significant. In addition, the highest category of coffee intake varied between Heliovaara et al. cohort study from Finland where the highest category included drinking up to 13 cups per day, compared to US studies where it was very unusual to have > 4 cups coffee intake per day. Combining the data of the cohort and case-control studies showed a significant association between total coffee intake and RA incidence (RR = 1.217, 95 % CI = 1.083-1.368,p = 0.001). Meta-analysis stratified by seropositivity indicated a significant association between coffee consumption and seropositive RA risk (RR=1.309, 95 % CI=1.142-1.499, p=1.1x10-5), but not seronegative RA risk (RR=1.097, 95 % CI=0.886-1.357, p=0.396). There was no significant association between decaffeinated coffee consumption and RA incidence (RR=1.709, 95 % CI 0.786-3.715), or between caffeinated coffee consumption and RA incidence (RR=1.055, 95 % CI 0.782-1.421). [corrected].