The Influence of Metabolic Syndrome in Predicting Mortality Risk Among US Adults

Importance of Metabolic Syndrome Even in Adults With Normal Weight

Ting Huai Shi, BA; Binhuan Wang, PhD; Sundar Natarajan, MD, MSc


Prev Chronic Dis. 2020;17(5):E36 

In This Article

Abstract and Introduction


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/m2], overweight [25.0 to <30.0 kg/m2], and obese [≥30.0 kg/m2]) 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.


Although obesity is a well-known risk factor for poor metabolic health,[1,2] metabolic health issues such as insulin resistance and diabetes risk also affect normal-weight people.[3] A useful method for assessing metabolic health is to determine the presence of metabolic syndrome (MetS), which is defined as having 3 of the following 5 criteria: central obesity, elevated blood glucose, elevated triglycerides, low levels of high-density lipoprotein cholesterol, and elevated blood pressure.[4]

Although obesity and MetS are related, several subsets of people who have a body mass index (BMI) within the normal range meet the criteria for MetS.[3] An important area of study is the influence of MetS on clinical outcomes among people in various weight categories. Most studies of MetS have focused on obese people; little attention has been paid to normal-weight people, despite their risk of MetS and the complications it may portend. The risk of MetS among normal-weight people may be a more relevant public health problem now because of the increasing prevalence of MetS across all weight categories in recent years.[5] Research that includes metabolically unhealthy normal-weight people shows equivocal results. Although several studies from around the world found an increased risk of diabetes or cardiovascular disease[6–11] among metabolically unhealthy normal-weight people, studies have not found an elevated risk of all-cause mortality in this group. Neither of 2 studies that used the US National Health and Nutrition Examination Survey (NHANES III) database stratified by MetS and BMI categories found significantly higher mortality in the group of adults with normal weight and MetS compared with a group of normal-weight adults without MetS.[12,13]

To better understand the relationship between weight and MetS and how this relationship can be generalized to the US population, we used data from the 1999–2010 National Health and Nutrition Examination Survey (Continuous NHANES) to examine how mortality risks differ among groups of adults classified according to weight and presence/absence of MetS. We focused on people with normal weight and MetS. This information may help to refine prevention and treatment strategies among groups of people in various weight categories with and without MetS.