The present cohort study, comprising 2,781 subjects in Beijing Tongren Hospital, focused on detecting how the incidence of MetS changed relative to BP level and what MetS components tend to emerge and change during a 5-year follow-up period. Our study revealed that the higher the BP at baseline, the higher the incidence of MetS at a later stage. We identified that people with different levels of BP would develop different combinations of risk factors. On analyzing the change in risk factors, we found that people with high BP tended to have impaired fasting glucose as the most common additional and new-onset MetS component, and that people with a lower BP level developed raised BP as the initial risk factor of MetS.
SBP and DBP of people with optimal and normal blood pressure at baseline tended to increase with time, while the SBP or DBP dropped in the subjects with high-normal and high blood pressure, according to original Tables 1 and 2. People with high-normal and high blood pressure may be more alert to their health as health education and promotion programs are popular in varies media in Beijing, possible actions could be intentionally or unintentionally taken, and their SBP/ DBP is, therefore, controlled or even lowered.
An association between raised BP and MetS has been reported as the most common MetS component , or even serves as an independent predictor for CVD . Several studies with structural equation modeling indicated that hypertension might play both a direct and indirect roles in the development of MetS [25–27]. However, physiologically, it is not easy to connect insulin-resistance with MetS . In the present study, we found that people with optimal and normal BP tended to have a relative lower incidence of MetS after 5 years comparing with people with high BP, and were less susceptible to developing the disorder. Most subjects who started off as “healthy” remained “healthy”, similar to a previous study in a German population . However, abnormal BP tended to be the first risk factor for MetS. About 17% of subjects with high-normal BP returned to “healthy”, while 12% continued to be in the condition.
By analyzing the shifts in MetS components, we found that raised BP was the most common risk factor for all groups. Previous studies have also shown that hypertension was the most important MetS component for men and one of the three most important components for women . Previous study suggested that prehypertension (SBP = 120–139 mmHg, and/or DBP = 80–89 mmHg) was predictive for risk of MetS .
In our study, subjects with high BP tended to have impaired fasting plasma glucose as a secondary risk factor. This is accordance with other studies, which found that raised fasting glucose was the second common component of MetS and people with MetS tended to have a disorder of glucose metabolism . Prehypertension may be an end-point related to each of the other four components. It is mainly a consequence of systemic low-grade inflammation and apoA-I dysfunction. In addition to the five components of MetS, prothrombotic and proinflammatory states are essential features based on the evidence of impaired function of HDL and apo A-I particles is discernible by biological evidence of functional defectiveness via outcomes studies and/or correlations with inflammatory and anti-inflammatory biomarkers . The aggregation to lipoprotein (Lp)(a) of apolipoprotein (apo) A-I underlies HDL dysfunction, and is an independent risk factor of magnitude similar to conventional components of MetS . Some studies indicated that proinflammatory state and oxidative stress are crucial for cardiometabolic disorders. Factors such as creatinine, platelet-activating factor, acetylhydrolase, thyroid stimulating hormone, acylation-stimulating protein, asymmetric dimethylarginine, and serum lipoprotein (Lp) (a) are key to trigger systemic low-grade inflammation and enhanced autoimmune reactions, which may induce impaired glucose and metabolic syndrome .
In most circumstances, “healthy” was the predominant state, and people with a single risk factor tended to return to the “healthy” state. High-normal BP was a crucial status for MetS prevention. As hypertension has a low rate of awareness in China, it is an important preventable risk factor for MetS and CVD events .
The strengths of this research were that it was a longitudinal study of 5 years in a Chinese population with data of relatively good quality. The limitation was the lack of waist circumference as an indicator for central obesity; however, we used BMI for substitute according to the WHO expert consultation . As Tongren Hospital is located in the center of Beijing, bias may be that there were more people with an urban life style recruited for the research. In addition, this study was based on a population attending for routine health check-up. Further studies using the general population would be desirable.