News Article
Components of Metabolic Syndrome Independently Predict Mortality
Each of four risk factors associated with metabolic syndrome was an independent predictor of all-cause and cardiovascular mortality, based on results from a study of more than 35,000 Taiwanese adults aged 40 years and older.
Whether the predictive value of metabolic syndrome is greater than the predictive value of the risk factors that it comprises remains unclear, wrote Shan Pou Tsai, Ph.D., of the University of Texas, Houston, and colleagues.
But the results of this study must be considered in context, said Dr. Yehuda Handelsman, an endocrinologist in private practice in Tarzana, Calif. The researchers did not use the definition of metabolic syndrome established by the Adult Treatment Panel III (ATP III) of the National Cholesterol Education Program, Dr. Handelsman said in an interview. For example, the researchers used body mass index (BMI) instead of waist circumference, he noted.
"In Taiwan you can't use the American ATP III risk factors," Dr. Handelsman said, adding that it's important to remember that the definitions in this study may not be generalizable to other populations.
To assess the mortality risks from individual metabolic syndrome risk factors, the researchers reviewed data from 35,259 adults in a database of civil servants and teachers in Taiwan. The results were published in the October issue of Diabetes Research and Clinical Practice (2008;82:148-56).
The average age of the study population at their time of recruitment was 48 years for women and 52 years for men.
The study participants, 23,185 men and 12,074 women, were categorized as "normal," "predisease," "disease," or "metabolic syndrome" on the basis of four risk factors: glucose, systolic blood pressure, BMI, and triglyceride level.
Predisease was defined as the presence of prediabetes (glucose 110-125 mg/dL), prehypertension (120-139 mm Hg), preobesity (BMI 25-29.9 kg/m²), and borderline high triglyceride level (150-199 mg/dL).
Overall, the researchers found that the prevalence of the predisease risk factors was nearly four times higher than the prevalence of metabolic syndrome (40.2% vs. 10.6%).
The researchers compared mortality in the predisease, disease, and metabolic syndrome groups with that in the normal reference group and calculated the relative risks for all-cause mortality, mortality from cardiovascular disease (CVD), and mortality from CVD in patients with diabetes.
The relative risk for mortality from all causes, CVD, and CVD plus diabetes in subjects with metabolic syndrome, compared with subjects in the normal reference group, was 2.03, 3.56, and 4.75, respectively. The relative risk for mortality from all causes, CVD, and CVD plus diabetes in subjects with three or four predisease risk factors was 1.60, 2.90, and 3.36, respectively. These risks were lower, but not significantly lower, than the risks in the metabolic syndrome group.
The researchers also analyzed relative risk for mortality among smokers and nonsmokers separately to control for the impact of smoking on CVD. In the subgroup of nonsmokers with three or four risk factors, the relative risk for mortality from all causes, CVD, and CVD plus diabetes was significantly higher, compared with the reference group (2.07, 4.39, and 5.38, respectively) and similar to the risk for those with metabolic syndrome (2.34, 4.55, and 6.01, respectively).
Even the presence of at least one predisease risk factor was a significant independent predictor of increased mortality risk, compared with the normal reference group, the researchers noted.
When the risk factors were examined individually, the relative risk for mortality from all causes for the entire cohort was 1.13 for prediabetes, 1.22 for prehypertension, 1.23 for preobesity, and 1.17 for borderline hypertriglyceridemia. Controlling for smoking did not reduce the risk: The mortality risk associated with each factor in the nonsmoker subgroup was higher than the mortality risk in the reference group.
"We found that the presence of any one of the four ‘predisease' factors even in the absence of any coexisting ‘disease' was able to predict subsequent increase" in all-cause and CVD mortality risk, the researchers wrote.
The study was limited by its homogeneous population of white-collar workers, and more research is needed to confirm the results in diverse populations. But the researchers emphasized that the study's value lies in the predictability of 15-year mortality risk by assessing several risk factors independently in a single examination. The researchers stated that they had no financial conflicts to disclose.
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