Background & aims: A causal association of non-alcoholic fatty liver disease (NAFLD) with cardiovascular disease (CVD) and type 2 diabetes (T2DM) remains unproved. We aimed to quantify the likelihood of causality examining the sensitivity of observational associations to possible confounding.
Methods: Studies investigating longitudinal associations of NAFLD with CVD or T2DM were searched on 5 June 2018. Study-specific relative risks (RRs) were combined in random-effects meta-analyses and pooled estimates used in bias analyses.
Results: Associations of NAFLD with CVD and T2DM were reported in 13 (258 743/18 383 participants/events) and 20 (240 251/12 891) studies respectively. Comparing patients with NAFLD to those without, the pooled RR was 1.48 (95% CI: 0.96, 2.29) for CVD and 2.17 (1.77, 2.65) for T2DM. In bias analyses, for an unmeasured confounder associated to both NAFLD and CVD with a RR of 1.25, the proportion of studies with a true (causal) effect of NAFLD on CVD surpassing a RR of 1.10 (ie, 10% increased risk of CVD in participants with NAFLD) was 0.67 (95% CI: 0.42, 0.92) while for 75% increase, it was 0.36 (0.11, 0.62). Corresponding figures for T2DM were 0.97 (0.91, 1.00) for a 10% increased risk of T2DM in participants with NAFLD to 0.70 (0.49, 0.92) for a 75% increase.
Conclusions: The results of this study are strongly suggestive for a causal relationship between NAFLD and T2DM, while the evidence for a causal link between NAFLD and CVD is less robust. Therapeutic strategies targeting NAFLD are likely to reduce the risk of developing T2DM.
Keywords: bias analysis; cardiovascular disease; causality; diabetes; meta-analysis; non-alcoholic fatty liver disease.
© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.