Gamma-glutamyltransferase levels and risk of metabolic syndrome: a meta-analysis of prospective cohort studies

Aims: Several epidemiological studies suggested that gamma-glutamyltransferase (GGT) levels may be associated with risk of Metabolic Syndrome (MetS). However, the exact association between them is still not fully clear. We therefore conducted a meta-analysis of prospective cohort studies to comprehensively evaluate the exact association between GGT and risk of MetS. Methods: The Pubmed, Embase, Science Citation Index (ISI Web of Science) databases were searched to collect all prospective cohort studies on the association between GGT and MetS. Then, the association between GGT and MetS was analysed in qualitative and quantitative manners. Results: Nine prospective cohort studies involving 47,499 participants and 5009 cases of MetS were included. When comparing the risk of MetS between the highest versus the lowest category of GGT levels, the pooled RR of MetS was 1.63 (95% CI: 1.431.82; p < 0.000). The second dose-response analysis of GGT levels per 5 U/l increment with risk of MetS showed that the summary RR of MetS was 1.09 (95% CI: 1.061.13; p < 0.000). Subgroup analysis suggested that number of adjusted confounding factors may be a potential source of heterogeneity. Sensitivity analyses showed that no single study significantly influenced the pooled RRs. Conclusions: Our results show that GGT levels are positively associated with risk of MetS independently of alcohol intake. GGT may be a promising marker for predicting MetS. Further studies are needed to confirm our findings and elucidate the underlying mechanisms in future.