The Influence of Metabolic Syndrome in Predicting Mortality Risk Among US Adults: Importance of Metabolic Syndrome Even in Adults With Normal Weight

INTRODUCTION: Although metabolic syndrome (MetS) is less prevalent among normal-weight adults than among overweight and obese adults, it does occur. The objective of our study was to examine how mortality risks differed in weight categories stratified by presence/absence of MetS. METHODS: We linked data for US adults responding to the National Health and Nutrition Examination Survey from 1999 through 2010 to data released from the National Death Index up to 2011. We grouped data according to categories of body mass index (normal [18.5 to <25.0 kg/m(2)], overweight [25.0 to <30.0 kg/m(2)], and obese [≥30.0 kg/m(2)]) and presence/absence of MetS. After conducting unadjusted analyses, we used Cox proportional hazards models to evaluate mortality risk as multivariable hazard ratios among obesity–MetS categories while controlling for selected covariates. RESULTS: The analysis included 12,047 adults. The prevalence of MetS was 61.6% in the obese group, 33.2% in the overweight group, and 8.6% in the normal-weight group. The multivariate adjusted hazard ratio (95% confidence interval) for mortality among the obesity–MetS groups, compared with the normal-weight–no-MetS group, were as follows: normal-weight–MetS (1.70 [1.16–2.51]), overweight–no-MetS (0.99 [0.77–1.28]), overweight–MetS (1.10 [0.85–1.42]), obese–no-MetS (1.08 [0.76–1.54]), and obese–MetS (1.30 [1.07–1.60]); differences were significant only for the normal-weight–MetS group and obese–MetS group. CONCLUSION: MetS is a risk factor for mortality among normal-weight and obese adults. In our study, normal-weight adults with MetS had the highest mortality among the 6 groups studied, suggesting that interventions should also focus on MetS patients with normal weight.