Independent association of metabolic syndrome severity score and risk of diabetes: findings from 18 years of follow-up in the Tehran Lipid and Glucose Study

Objectives This study aimed to investigate the association between age-specific and sex-specific continuous metabolic syndrome severity score (cMetS-S) and the risk of developing type 2 diabetes mellitus (T2DM). Additionally, the study aimed to assess the added value of cMetS-S in predicting T2DM compared with traditional MetS criteria. Design The study used a longitudinal cohort design, following participants for 18 years. Setting The research was conducted within the Tehran Lipid and Glucose Study, a community-based study in Tehran, Iran. Participants A total of 6957 participants aged 20-60 years were included in the study. Interventions/exposures The cMetS-S of each participant was determined using age-specific and sex-specific equations and Cox proportional hazard regression models were used to analyse the association between cMetS-S and T2DM using continuous and quantile approaches. Primary and secondary outcome measures The outcome measure was the association between cMetS-S and the development of T2DM during the 18-year follow-up. Results A total of 1124 T2DM cases were recorded over 18 years of follow-up. In the fully adjusted model, a 1-SD increase in the cMetS-S was associated with future T2DM (HR 1.72; 95% CI 1.54 to 1.91). Men and women had HRs of 1.65 (95% CI 1.40 to 1.95) and 1.83 (95% CI 1.59 to 2.10) for T2DM per 1-SD increase in cMetS-S, respectively. Higher cMetS-S was associated with increased risk of diabetes in both prediabetic (HR 1.42;95% CI 1.23 to 1.64) and normoglycaemic individuals (HR 2.11;95% CI 1.76 to 2.54); this association was more significant in normoglycaemic individuals. Unlike the traditional-based MetS definitions, the cMetS-S improved diabetes prediction (p<0.001). Conclusions The cMetS-S is strongly associated with future diabetes in prediabetic and normoglycaemic individuals independent of MetS components during a long term. As the relationship between cMetS-S and T2DM is more pronounced in normoglycaemic individuals than in those with pre-diabetes, implementing the evaluation of cMetS-S can serve as an early identification tool for individuals at risk of T2DM prior to the onset of pre-diabetes.