CORRESPONDENCE: LETTER TO THE EDITOR
Is the Metabolic Syndrome a Cardiovascular Risk Factor Beyond Its Specific Components?
Sandro Inchiostro, MD*,
Gian Paolo Fadini, MD,
Saula Vigili de Kreutzenberg, MD, PhD,
Nadia Citroni, MD and
Angelo Avogaro, MD, PhD
* Dipartimento di Medicina Interna, U.O. Medicina II, Ospedale S. Chiara, via Largo Medaglie d’oro, 38100, Trento, Italy (Email: sinchio{at}tin.it).
The discussion about the cardiovascular risk conferred by the metabolic syndrome (MetSyn) is an actual topic, and we read the meta-analysis about this argument published by Gami et al. (1) with interest. A crucial point concerns the following question: is the risk associated with the MetSyn greater (synergic) than the sum of the risk components conferred by the individual factors that define the syndrome? If the answer is yes, the MetSyn should be recognized as a specific entity and taken into account for correct evaluation of cardiovascular risk; whereas if the answer is no, it should be sufficient to treat the individual factors of the MetSyn without paying attention to its presence.
Even if the results reported in the study’s abstract (1) correctly affirm that the MetSyn predicts cardiovascular events after adjustment for traditional cardiovascular risk factors, the message reported in the text is different. In fact, Gami et al. (1) affirm that the MetSyn increases "risk of cardiovascular disease or death..., even after controlling for its component risk factors," thus reinforcing this concept in the Discussion section where they state that "the analysis...demonstrates that the MetSyn confers cardiovascular risk beyond that which is associated with its component risk factors" and concluding that "in addition to targeting individual cardiovascular risk factors primary prevention trials should study interventions that address the MetSyn as one entity." The datum supporting these assertions was the meta-analysis of three studies (2–4) that adjusted the risk conferred by the MetSyn for several traditional risk factors but not for the specific components of the MetSyn.
Moreover, careful analysis of the three studies leads to a different conclusion. In the ARIC (Atherosclerosis Risk In Communities) study, McNeill et al. (2) adjusted the risk associated with the MetSyn for its components, reporting a hazard ratio (HR) of coronary heart disease of 0.91 (95% confidence interval [CI] 0.67 to 1.23) for men and 0.71 (95% CI 0.45 to 1.14) for women, "indicating that the risk of coronary heart disease associated with the syndrome was not in excess of the level explained by the presence of its individual components." In the WOSCOPS (West of Scotland Coronary Prevention Study), Sattar et al. (3) affirm that "possession of the MetSyn was not a significant predictor in the presence of the effects of its individual components when investigated in a multivariate model."
Finally, Schillaci et al. (4) reported an HR associated with the MetSyn of 1.73 (95% CI 1.25 to 2.38), after adjustment for blood pressure as the only component of the MetSyn, without mention of any analysis adjusting the risk associated with the MetSyn for its specific components. In conclusion and in agreement with recent observations (5,6), no study cited supports a synergic effect of the individual factors of the MetSyn on cardiovascular risk, excluding, at the moment, the necessity to consider the MetSyn as a specific cardiovascular risk factor beyond its components.
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References
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1. Gami AS, Witt BJ, Howard DE, et al. Metabolic syndrome and risk of incident cardiovascular events and death: a systematic review and meta-analysis of longitudinal studies J Am Coll Cardiol 2007;49:403-414.[Abstract/Free Full Text]2. McNeill AM, Rosamond WD, Girman CJ, et al. The metabolic syndrome and 11-year risk of incident cardiovascular disease in the Atherosclerosis Risk in Communities study Diabetes Care 2005;28:385-390.[Abstract/Free Full Text] 3. Sattar N, Gaw A, Scherbakova O, et al. Metabolic syndrome with and without C-reactive protein as a predictor of coronary heart disease and diabetes in the West of Scotland Coronary Prevention Study Circulation 2003;108:414-419.[Abstract/Free Full Text] 4. Schillaci G, Pirro M, Vaudo G, et al. Prognostic value of the metabolic syndrome in essential hypertension J Am Coll Cardiol 2004;43:1817-1822.[Abstract/Free Full Text] 5. Sundstrom H, Vallhagen E, Riserus U, et al. Risk associated with the metabolic syndrome versus the sum of its individual components Diabetes Care 2006;29:1673-1674.[Free Full Text] 6. Iribarren C, Go AS, Husson G, et al. Metabolic syndrome and early-onset coronary artery disease: is the whole greater than its parts? J Am Coll Cardiol 2006;48:1800-1807.[Abstract/Free Full Text]
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