We read with interest the letter written by Holvoet and colleagues referring to our article published recently in Arteriosclerosis, Thrombosis, and Vascular Biology.1 Holvoet et al discuss reasons for our failure to find increased concentrations of circulating oxidized LDL (oxLDL) in subjects with the metabolic syndrome, a relationship that they2 and others3 have reported previously.
Their first point relates to the use of different definitions of the metabolic syndrome. This point is discussed in our article.
Their second point relates to subject recruitment. They suggest that our stringent exclusion criteria (eg, exclusion of subjects with diabetes mellitus, antihypertensive drug treatment, or a BMI >35 kg/m2) could have affected the relationship between the metabolic syndrome and circulating oxLDL concentrations. Because the characteristics of our cohort are very similar to those of Sigurdardottir et al,3 a cohort in which higher oxLDL concentrations were associated with the metabolic syndrome, we think that this explanation is unlikely. This point is discussed in our article.
Their third suggestion is that small sample size limited our statistical power. This point is discussed in our article.
Their fourth suggestion is that there are fundamental metabolic differences between populations, possibly caused by differences in genetic architecture. However, they say that this seems unlikely. We agree, especially because Sigurdardottir et al3 investigated subjects with an almost identical genetic background (healthy men with Swedish ancestry) to those in our study.
Their final point relates to our failure to adjust oxLDL for LDL-cholesterol concentrations. In our cohort oxLDL concentrations adjusted for LDL-cholesterol were not elevated in the metabolic syndrome.
Thus we thank Holvoet et al for their comments on our study, but consider that to a great extent we had addressed their points in our article.
Sjogren P, Basu S, Rosell M, Silveira A, de Faire U, Vessby B, Hamsten A, Hellenius M-L, Fisher RM. Measures of oxidized low-density lipoprotein and oxidative stress are not related and not elevated in otherwise healthy men with the metabolic syndrome. Arterioscler Thromb Vasc Biol. 2005; 25: 2580–2586.
Holvoet P, Kritchevsky SB, Tracy RP, Mertens A, Rubin SM, Butler J, Goodpaster B, Harris TB. The metabolic syndrome, circulating oxidized LDL, and risk of myocardial infarction in well-functioning elderly people in the Health, Aging, and Body Composition cohort. Diabetes. 2004; 53: 1068–1073.