The metabolic syndrome is associated with a 2-fold increase in cardiovascular outcomes and a 1.5-fold increase in all-cause mortality. Studies are needed to investigate whether or not the prognostic significance of the metabolic syndrome exceeds the risk associated with the sum of its individual components. Furthermore, studies are needed to elucidate the mechanisms by which the metabolic syndrome increases cardiovascular risk.

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Atrial fibrillation (AF) is one of the most clinically diagnosed cardiac disturbances but little is known about its risk factors. Previous epidemiological studies have reported on the association between diabetes mellitus (DM) and subsequent risk of AF with inconsistent results. The aim of this study was to conduct a meta-analysis of published studies to reliably determine the direction and magnitude of any association between DM and AF. A systematic review and meta-analysis was conducted. PUBMED and EMBASE were searched to identify prospective cohort and case-control studies that had reported on the association between DM and other measures of glucose homeostasis with incident AF by April 2010. Studies conducted in primarily high-risk populations and participants in randomized controlled trials were excluded. Seven prospective cohort studies and four case-control studies with information on 108,703 cases of AF among 1,686,097 individuals contributed to this analysis. The summary estimate indicated that individuals with DM had an approximate 40% greater risk of AF compared with unaffected individuals: RR 1.39 (95% Confidence Intervals: 1.10 – 1.75; p for heterogeneity <0.001). After correcting for publication bias the RR was XXXXXXX. Studies that had adjusted for multiple risk factors reported a smaller effect estimate compared with age-adjusted studies: RR 1.24 (95% Confidence Intervals: 1.06 – 1.44) versus 1.70 (1.29 – 2.22); p for heterogeneity = 0.053. The population attributable fraction of AF due to DM was 2.5% (95% CI: 0.1 – 3.9%). In conclusion, DM is associated with an increased risk of subsequent AF but the mechanisms that may underpin the relation between DM and AF remain speculative.