Metabolic syndrome and the risk of stroke

Introduction
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By Douglas J Lanska MD MS MSPH

The frequent simultaneous presence of obesity, hypertension, dyslipidemia, and diabetes was first recognized in the late 1960s, was labeled the "metabolic syndrome" and associated with atherosclerosis by the late 1970s, and linked to insulin resistance syndrome in the 1990s (Ferrannini et al 1991; Meigs et al 1997; Alexander et al 2003). Only recently has the metabolic syndrome been linked to cerebrovascular atherosclerosis and strokes (Chen et al 2006; Kurl et al 2006; Ovbiagele et al 2006).

The underlying pathophysiology of the metabolic syndrome has yet to be fully defined, but intra-abdominal fat is independently associated with all 5 of the metabolic syndrome criteria suggesting that it may have a pathophysiological role (Carr et al 2004). Of the NCEP ATP III criteria, increased waist circumference and hypertriglyceridemia best identify insulin resistance and visceral adiposity (Carr et al 2004).

Metabolic syndrome is very common, affecting about 44% of the adult population of the United States over the age of 50 years (Alexander et al 2003). Age-adjusted prevalence of the metabolic syndrome increases significantly as a function of degree of impairment of glucose tolerance (Alexander et al 2003).

Glucose Tolerance Percent of Population Prevalence of Metabolic Syndrome
Normal fasting glucose 57% 26%
Impaired glucose tolerance 14% 33%
Impaired fasting glucose 12% 71%
Diabetes mellitus 17% 86%

Metabolic syndrome and diabetes contribute to the prevalence of coronary heart disease (Alexander et al 2003).

  • The excess prevalence of coronary heart disease attributable to metabolic syndrome is 37% in those without diabetes and 55% in those with diabetes (Alexander et al 2003).
  • All 5 metabolic syndrome criteria are established coronary heart disease risk factors, but it is unclear if the risk factor constellation comprising the metabolic syndrome confers additional risk beyond the sum of the component parts.
  • Some studies (eg, Alexander et al 2003) suggest that the risk of coronary heart disease from metabolic syndrome is derived particularly from the HDL cholesterol and blood pressure components.
  • Nevertheless, the presence of metabolic syndrome is associated with a 2-fold increased risk of coronary heart disease and is a "convenient way to encapsulate a number of proven risk factors" (Alexander et al 2003).
Risk Category Percent of Population Prevalence of Coronary Heart Disease
No metabolic syndrome or diabetes 54% 9%
Diabetes but no metabolic syndrome 2% 2%
Metabolic syndrome but no diabetes 29% 14%
Diabetes and metabolic syndrome 15% 19%