The constellation of risk factors known as the metabolic syndrome was associated with a 1.5-fold increase in all-cause mortality and a 2-fold increase in cardiovascular outcomes, in a meta-analysis published online Sept. 20 in the Journal of the American College of Cardiology.
“The value of the metabolic syndrome as a predictor of cardiovascular risk has been met with much debate,” wrote Salvatore Mottillo of the Jewish General Hospital and McGill University, Montreal, and his colleagues.
The researchers reviewed data on 951,083 patients from 87 prospective, observational studies of cardiovascular risk and metabolic syndrome based on either the National Cholesterol Education Program (NCEP) definition of three or more of five cardiovascular risk factors, or the revised NCEP (rNCEP) issued in 2004.
The five factors in the NCEP definition are waist circumference (greater than 88 cm for women and greater than 102 cm for men), triglycerides (150 mg/dL or higher for men and women), systemic hypertension (130/85 mm Hg or higher), HDL cholesterol level (less than 50 mg/dL for women and less than 40 for men), and fasting glucose of 110 mg/dL or higher. The revised version dropped the fasting glucose to 100 mg/dL or higher and modified the central obesity measurements to be greater than or equal to 102 cm for men and greater than or equal to 88 cm for women.
Some of the studies involved more than one cardiovascular risk factor and more than one definition of metabolic syndrome.
Overall, metabolic syndrome was associated with an increase in all-cause mortality, with a relative risk of 1.54 based on the NCEP definition and 1.63 based on the rNCEP definition. In a pooled analysis, the risk of cardiovascular disease mortality approximately doubled (relative risk, 2.40), as did the risk for cardiovascular disease (relative risk, 2.35), stroke (relative risk, 2.27), and myocardial infarction (1.99).
Metabolic syndrome remained significantly associated with an increased risk of cardiovascular disease (CVD) mortality in patients without type 2 diabetes, the researchers noted. The relative risks of cardiovascular outcomes in individuals without type 2 diabetes were 1.62 for MI, 1.75 for CVD mortality, and 1.86 for stroke (J. Am. Coll. Cardiol. 2010;56:1113-32).
“We therefore suggest that the metabolic syndrome does not require type 2 diabetes mellitus in its definition in order to be closely associated with cardiovascular risk,” the researchers wrote.
The results were limited by the use of observational studies and the variation in follow-up times. However, in a sensitivity analysis, the risk for CVD mortality associated with metabolic syndrome was similar in studies with follow-up times both longer and shorter than the median time.
Prospective studies of cardiovascular risk associated with metabolic syndrome itself, rather than the different components, are needed, “in order to establish whether or not the metabolic syndrome adds any prognostic significance,” the researchers said. Meanwhile, “we recommend that health care workers use the metabolic syndrome to identify patients who are at particularly high risk for cardiovascular complications,” they said.
Mr. Mottillo was supported by a Canadian Institutes of Health Research grant in cardiovascular outcomes research. Study coauthor Dr. Jacques Genest is on the speakers bureau for Merck & Co. and AstraZeneca.