In this section, we review whether there is incremental risk when these comorbidities cluster as the metabolic syndrome in patients with HF. The metabolic syndrome constitutes a clustering of risk factors that include elevated glu- cose, hypertension, central obesity, and dyslipidemias, namely hypertriglyceridemia and low high-density lipo- Although the underlying cause of the syn- drome remains poorly understood, insulin resistance and central obesity are thought to play a key role. A variety of organizations have proposed definitions for the metabolic syndrome,288 291 and there are some ca- veats in the application of the various definitions of the metabolic syndrome. The risk factors included in the metabolic syndrome are continuous and may impart varying degrees of risk across the spectrum of values. Instead, the definitions have been used in a dichoto- mous manner with risk assessed as above or below a cut point. In addition, each criterion of the definition is given equal weight toward the diagnosis of the metabol- ic syndrome. Lastly, unmeasured or related conditions such as chronic inflammation, prothrombotic milieu, polycystic ovary syndrome, nonalcoholic steatohepa- titis, cholesterol gallstones, and sleep apnea may be associated with the metabolic syndrome. Impact of the Metabolic Syndrome on Incident HF A number of studies have demonstrated that the pres- ence of the metabolic syndrome translates into an in- creased risk of developing HF. NHANES III (Third National Health and Nutrition Examination Survey; 1988 1994) reported an association between the metabolic syn- drome and HF.292 Participants with the metabolic syn- drome were twice as likely to report HF. The prevalence of HF increased with the number of components of the metabolic syndrome. 