Metabolic syndrome (MetS) is a cluster of conditions characterized by abdominal obesity, dyslipidemia, elevated blood pressure, and hyperglycemia. Nearly 34.7% of adults in the United States (U.S.) have metabolic syndrome.1 MetS has been linked to adverse health outcomes such as cardiovascular disease (CVD),2 chronic kidney disease (CKD),3 cancer,4 and mortality.5 Identifying factors associated with MetS, especially modifiable lifestyle factors, is necessary to reduce the disease burden and prevent subsequent health consequences.

Combustible cigarette smoking is a well-established risk factor for MetS.6 Electronic cigarettes (e-cigarettes), alternatives to combustible cigarettes, have been introduced into the U.S. market since 2007 and gained increasing popularity in recent years.7 4.7% of U.S. adults were active e-cigarette users in 2021.8 Although e-cigarettes are usually considered less hazardous than conventional combustible cigarettes which may assist smoking cessation and reduce smoking-attributable mortality, toxic chemicals generated by e-cigarettes’ liquids and aerosols such as nicotine, carbonyl compounds, and heavy metals still raise concerns regarding health risks.9, 10

Emerging evidence is showing e-cigarette use is associated with health outcomes such as lung injury,11 cardiovascular diseases,12 prediabetes,13 and mental disorders.14 Animal studies indicated that e-cigarette exposure (especially nicotine) was significantly associated with insulin resistance, hyperglycemia, accumulation of lipids of diverse sizes in hepatocytes, and obesity.15, 16, 17 However, few studies have examined the association between e-cigarette use or dual use of e-cigarettes and combustible cigarettes and MetS on the population level. Existing cross-sectional studies on the association between e-cigarette use or dual use and MetS are mainly limited to Korean adults,18, 19, 20, 21 leaving little evidence of those associations among the U.S. population.

To address those research gaps, we conducted a cross-sectional study using data from the National Health and Nutrition Examination Survey (NHEANES). To the best of our knowledge, this is the first study that examines the association between e-cigarette use or dual use of e-cigarettes and combustible cigarettes and MetS in the U.S. population. Identifying the association between e-cigarette use or dual use and MetS may add evidence for modifiable lifestyle factors associated with MetS and provide insights for tobacco control policies and future longitudinal studies.