Validation of the Sex Difference in the Trend of Carotid Artery Intima Media Thickness by the Number of Metabolic Components

To the Editor: Hartley et al1 examined the association between metabolic syndrome (MetS) and the carotid artery intima media thickness (IMT) in male and female police officers. They measured three carotid IMT variables, and the mean common carotid artery (CCA) IMT was measured in 12 CCA segments measuring approximately 10 mm in length: the near and far wall and, from three interrogation angles, on both the right and left sides (2 walls × 3 angles × 2 sides = 12). I would be very interested in the sex difference of the mean carotid artery IMT, especially the mean CCA-IMT, stratified by the number of MetS components. Although Iglesias del Sol et al2 examined the differences in the predictive ability of the measurement sites for future myocardial infarction and concluded that the IMT of the CCA, carotid bifurcation, and internal carotid artery showed the same predictive ability, Polak et al3 reported a cohort survey and showed that the CCA-IMT, rather than the IMT at the carotid artery bulb and internal carotid arteries, can be explained by traditional cardiovascular risk factors. Hartley et al1 conducted an analysis of variance with statistical adjustments for age, smoking status and low-density lipoprotein cholesterol. In addition, a trend test was performed to check the linearity of the IMT values. The results revealed that the unadjusted mean CCA-IMT was significantly and positively associated with number of MetS components among 106 women and among 304 men, respectively. However, the significant association was no longer seen among men after the adjustments. The percentage of subjects younger than 50 years was 84.6% in the males and 91.6% in the females in their study. The prevalence of MetS in their study was 26.1% but its prevalence in the male officers was higher than that in the female officers (32.2% vs 8.5%). In addition, a half of the female officers had no MetS components. Several reports have indicated that the influence of MetS on the early progression of atherosclerosis may be stronger in women than in men,4–7 which lends support to the sex-related difference presented by Hartley et al.1 However, the age and occupation of the subjects varied among the reports. Is this result related to occupational factors? I want to present the opposite results by fitting the same analysis procedure as that conducted by Hartley et al.1 A total of 771 subjects (669 males and 102 females) were included in our intensive health examination. Their age ranged from 35 to 59 years and the mean (standard deviation) ages were 45.8 (7.0) years in males and 49.5 (7.2) years in females. The type of job could not be specified, and percentages of workers with income were 93.8% in males and 50.0% in females in this study. The prevalence of MetS was 28.7% in the males and 15.7% in the females and the percentage of subjects with no MetS components was 23.9% in the males and 36.3% in the females. The CCA-IMT was measured on the left and right sides separately; although, the left-right difference could not be recognized in the trend analysis. This study was with the approval of the institutional review board at Ota General Hospital, Gunma Prefecture, Japan (July 17, 2010). As presented in Table 1, the unadjusted and adjusted mean CCA-IMT was significantly and positively associated with the number of MetS components among males. However, there was no significant association among the females. Hartley et al1 recommend a larger population study, especially for females, and a longitudinal analysis. I agree with their proposal, as understanding of the gender-specific mechanisms underlying these results will help in concluding whether a significant association between the number of MetS components and the CCA-IMT might exist only among females.