| Background and objectiveCardiovascular disease (CVD) is a common kind of non-communicable disease, which places a high burden of morbidity on modern populations in the world. It was reported that there were at least 230 million people suffered from CVD in our country. About 3 million patients died due to CVD. It was also reported that CVD incidence and mortality in China were projected to increase.Besides those classical risk factors of CVD, including hypertension, diabetes mellitus, cigarette smoking and obesity, heart rate has attracted more attention in the past decades. Some previous studies pointed out that elevated heart rate could be regarded as a risk marker of CVD, but the opinion was still controversy and inconsistency, especially for the association with the incidence of CVD. And the information in Chinese adults was still scarce.It has been shown that socio-economic disparities were related to risk of CVD when socio-economic status (SES) was defined by occupational status or education in high-income countries from America and Europe. Association within SES and the risk of cardiovascular disease are less consistent in low- and middle-income countries. As far as we know, seldom reports about association within SES and CVD have been published in Asia.We used data from a large, prospective cohort study in Chinese adults with a nationally representative sample to examine the influence of heart rate on the incidence of CVD in China. We also analyzed the relationship between SES (occupational or educational status) and the risk of CVD incidence and mortality in this population.Data and methodsA prospective study was conducted for 169,871 Chinese adults≥40 years of China National Hypertension Survey Epidemiology Follow-up Study (CHEFS) in 1991 and followed during 1999-2000 with a response rate of 93.4%. Heart rate, type of employment, educational background and other covariates were obtained at the baseline survey by a standard protocol.CVD was defined as a confirmed diagnosis of AMI or stroke or an underlying cause of death due to CVD (ICD-9:390.0-398.9,401.0-429.9 and 430.0-438.9) during the period of follow-up. Heart disease was defined as a confirmed diagnosis of AMI or an underlying cause of death (ICD-9:390.0-398.9 and 401.0-429.9); coronary heart disease (CHD), a confirmed diagnosis of AMI or an underlying cause of death (ICD-9:410.0-414.9); and stroke was defined as a confirmed diagnosis of stroke or an underlying cause of death (ICD9: 430.0-438.9).Hazard ratios (HRs) were estimated by Cox proportional hazard regression model. Heart rate was introduced as both a categorical (<60,60-74,75-89 and≥90 beat per minute [bpm]) and a continuous (per 10bpm increase) variable. Types of occupation were categorized into seven groups, including unemployed participants, farmer (farmer and others), worker (worker and service staff), retired group, clerk, professional and manager. Educational background was classified into four categories (illiterate, less then high school education, high school or technical school education, and college school education). A complex index was derived based on the sum scores of occupation and education. All the variables (including occupational, educational categories and the complex index) were analyzed as a dummy variable. The interaction between gender and the complex was also examined.Results1 Heart rate influence on incidence of cardiovascular disease among adults in ChinaAfter an average of 8.3 years' follow-up (836,811 person-years),6837 participants (3932 men,2905 women) developed into CVD.Compared with the participants with heart rate 60-74 bpm, men with 75-89 and≥90 bpm had higher risks of CVD and heart disease after multivariate adjustment. The HRs and 95% conference intervals (CIs) were 1.12(1.04,1.20) and 1.33(1.19,1.48) for CVD, and 1.17(1.05,1.30) and 1.51(1.28,1.77) for heart disease. Heart rate≥90 bpm in men increased the risks of CHD and stroke, the HRs and 95% CIs:1.52(1.27,1.80) and 1.18(1.02,1.37), respectively. Heart rate≥90 bpm increased women's risks of CVD, heart disease and CHD.The corresponding HRs and 95% CIs were 1.24(1.10,1.40),1.51(1.27,1.78) and 1.50 (1.24,1.81), respectively.Positive relationship between heart rate and CVD was also found in the analysis for clustering of CVD risk factors, subgroup analyses (in those age<65 years, normotensive and hypertensive groups) and sensitivity analyses.2 Socio-economic status predicting cardiovascular disease incidence and mortality in Chinese adultsThe total follow-up time was 855,662 person-years.7301 CVD events were occurred (4164 men,3137 women).(1) occupational status and cardiovascular disease incidence/mortalityTypes of occupations were categorized into seven groups, including unemployed participants, farmer (farmer and others), worker (worker and service staff), retired group, clerk, professional and manager. Baseline age, hypertension, cigarette smoking, alcohol consumption, body mass index, physical activity, higher heart rate (≥90bpm), geographic region, and urbanization were adjusted in the analysis.We found statistically significant inverse relationships between occupational status and risk of CVD, heart disease, stroke in both men and women (all p<0.01). In men, for CVD, compared with the unemployed participants, those in groups of worker, retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95% CIs:0.65(0.44,0.97),0.58(0.48,0.71),0.47(0.36, 0.62),0.36(0.28,0.46) and 0.42(0.32,0.54). For heart disease, those in groups of retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95% Cls:0.68(0.51,0.91),0.38(0.24,0.61),0.45(0.31,0.66)and0.50(0.34,0.73). For CHD, those in groups of clerk, professional and manager had lower risks, with corresponding HRs and 95% CIs:0.48(0.23,0.99),0.45(0.23,0.88) and 0.49(0.25, 0.96). For stroke, those in groups of retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95% CIs:0.52(0.40,0.69),0.48(0.33, 0.66),0.30(0.22,0.43) and 0.36(0.26,0.50). In women, only those in groups of clerk and professional had lower risks than in groups of unemployed participants, with corresponding HRs (95%Cls):0.58(0.36,0.92) and 0.65(0.46,0.92).We also found statistically significant inverse relationships between occupational status and risk of death from CVD, heart disease, stroke in both men and women (all p<0.01). In addition, we found significant inverse relationships between occuaptional status and death of CHD in men (p=0.002). In men, for all death, compared with the unemployed participants, those in groups of worker, retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95%Cls:0.65(0.49,0.86),0.63(0.55,0.73),0.44(0.36,0.55),0.31(0.26,0.38) and 0.38(0.31,0.46). For CVD, those in groups of retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95% Cls:0.64(0.51,0.78), 0.36(0.25,0.51),0.29(0.21,0.40)and 0.37(0.27,0.50). For heart disease, those in groups of clerk, professional and manager had lower risks, with corresponding HRs and 95% Cls:0.21(0.11,0.41),0.38(0.25,0.59)and 0.46(0.30,0.71). For CHD, those in groups of clerk, professional and manager had lower risks, with corresponding HRs and 95% Cls:0.23(0.08,0.70),0.28(0.12,0.66)and 0.36(0.16, 0.84). For stroke, those in groups of retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95% Cls:0.49(0.36,0.68),0.42(0.26,0.67), 0.21(0.13,0.34)and 0.28(0.18,0.44). In women, for for all death, compared with the unemployed participants, those in groups of farmer, retiree, clerk, professional and manager had lower risks, with corresponding HRs and 95%Cls:0.64(0.42, 0.99),0.79(0.68,0.92),0.46(0.31,0.69),0.42(0.32,0.57)and 0.60(0.39,0.92). For CVD, those in groups of clerk and professional had lower risks, with corresponding HRs and 95% Cls:0.41(0.20,0.86) and 0.33(0.18,0.58). For heart disease, those in groups of clerk, professional and manager had lower risks, with corresponding HRs and 95%Cls:0.20(0.05,0.84) and 0.29(0.13,0.66). For stroke, those in groups of professional had a lower risk, with corresponding HRs and 95%Cls:0.37(0.17,0.81).(2) Educational status and cardiovascular disease incidence/mortalityEducational background was classified into four categories (illiterate, less then high school education, high school or technical school education, and college school education). After multivariate adjustment, we found statistically significant inverse relationships between educational status and risk of CVD, heart disease and stroke in both men and women (all p<0.05). In addition, we also found statistically significant inverse relationships between educational status and risk of total,CVD, heart disease and stroke death in both men and women (all p<0.01). Educational status had an impressive effect on women, especially for stroke. Compared with illiterate, those in group of college school education had lower risks of CVD, heart disease and stroke.The corresponding HRs were only 35%,38% and 31% of the reference's in women; 50%,52% and 48% of the reference's in men.(3) Complex index and cardiovascular disease incidence/mortalityAfter multivariate-adjustment, we found inverse relationships between the comlex index and the risk of CVD incidence/mortality both in men and women. Statistically significant interaction between the complex index and gender was found (p<0.001 for risk of CVD incidence, and p=0.011 for CVD mortality). Compared with men accepted 0 score, women with≥5 scores had a lowest risk of CVD incidence, and the HR was reduced to 40% of the reference. Women with≥7 scores only had 17% of the CVD mortality risk of the reference.Conclusions1 Heart rate influence on incidence of cardiovascular disease among adults in ChinaElevated heart rate was associated with higher CVD incidence in Chinese adults, especially in men. This suggests that higher heart rate might be a risk marker for CVD incidence in Chinese adults.2 Socio-economic status predicting cardiovascular disease incidence and mortality in Chinese adultsOccupational social class has an inverse influence on the risk of CVD in Chinese adults aged≥40 years especially in men in this study population. Educational status was associated with risk of CVD in both men and women, especially in women. This suggests that special attention should be paid and special strategy should be made for cardiovascular disease prevention in the unprivileged Chinese adults.
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