Numerous studies have suggested that MS is a cluster of CVD risk factor[15–18]. A meta-analysis by Mottillo et al. that included 87 different studies found that MS was associated with an increased risk of CVD(relative risk: 2.35; 95% CI: 2.02–2.73). The predictive value of MS and its contribution to CVD should be ascertained in region-specific populations, considering that its effects have been studied in select populations. However, longitudinal data regarding the predictive value of MS in Kazakh population are sparse. In this study, MS was associated with CVD in Kazakh subjects, and the increased risks of CVD remained significant after adjusting for age, sex, drinking, and family history of hypertension, diabetes, and CVD. These findings were also reported in some earlier studies[22–25]. These results imply a significant role of MS in the development of CVD in this ethnic population. However, McNeill et al. found no significant correlation between MS and CVD in a biracial cohort of Whites and Blacks, even after adjusting for risks associated with MS components, a finding that was also highlighted in the West of Scotland Coronary Prevention Study. These discrepancies may be explained in part by the different MS definitions used and the prevalence of individual components of MS in the studied populations.
Our present study suggested that each component of MS was associated with an increased prospective risk of CVD. Furthermore, as the number of MS components increased, the risk of CVD also increased, exhibiting a significant and cumulative-component response trend. This suggests the presence of a cumulative effect of MS components in elevating the CVD risk. These findings are vital because the relationships between clustering patterns of MS and CVD risk have not been thoroughly characterized in Kazakh populations. This synergistic association is also noteworthy as it provides valuable information for the establishment of appropriate policies in preventive public health care for the inhabitants of Xinjiang. This linear synergistic correlation has been previously reported in other ethnic groups[24, 25].
Recently, there has been an increase in research concerning the independent association of MS and its components for predicting CVD. However, which MS component is associated with CVD to a larger degree remains unclear. In the Asia Pacific region, up to 66% of some subtypes of CVD can be attributed to hypertension. Numerous studies have suggested a more important role for BP than other components in determining cardiovascular events[29, 30]. Likewise, the present study found that after adjusting for 4 other MS components as well as age, sex, drinking, and family history of hypertension, diabetes, and CVD, the BP factor was still independently associated with increased risks of CVD in Kazakh population. A report by Iso et al. suggested that the National Cholesterol Education Program-defined MS was associated with CVD, even though the body mass index(BMI) was used instead of the Asian criterion for WC. Therefore, adjusting for BMI in models where WC may be entered would be an over adjustment. we did not adjust the BMI in the Cox regression models. The above studies were relatively consistent in finding that BP was an independent risk factor for the development of CVD.
Moreover, our results showed that BP, WC and TG were independent risk factors for CVD in the Kazakh population. Suh et al. found that BP and abdominal obesity were key predictors of CVD in Koreans when adjusted for general risk factors and MS components. For subjects in the National Health and Nutrition Examination Survey III, BP and HDL-C were associated with CHD when adjusted for general risk factors and MS components. Hadaegh et al.studied Middle-East Caucasian residents in Tehrani and highlighted that the FPG level in women and WC in men were independently associated with CVD. These reports are inconsistent in terms of the MS components that predict CVD. These discrepancies may be explained in part by the different study populations, follow-up periods, MS definition used, and prevalence of individual components of MS in different populations.
The present study found that BP, WC and TG were independent risk factors for CVD in Kazakhs, which requsted further consideration of whether WC and TG, WC / TG and BP interact for cardiovascular risk. As a result, we analyzed the interaction between TG and WC or between WC / TG and BP and explored whether their coexistence is an additional risk factor for CVD. Our results showed that when TG and WC coexisted, the aOR was 2.16, which indicated that the accumulation of TG and WC fortifies CVD risk. Therefore, it is plausible that the coexistence of TG and WC contribute to the highest CVD risk, as observed in this study. This indicates that the growing double epidemic of obesity and dyslipidemia among Kazakh people may greatly and rapidly increase their burden of developing CVD. However, the additive interaction indexes indicated no additive interaction between TG and WC. This result was consistent with the results obtained by Kang et al. The above phenomenon indicated that when multiple metabolic abnormalities occur at the same time, the risk of CVD caused by MS is not greater than the sum of their components, indicating that the presence of MS does not provide a clinician with more or better information. This may be because the MS components have a common physiological basis, such as inflammation, or central obesity, or are closely related to one another.