Incidence And Trends Of Prevalence Of Hypertension Subtypes Among Chinese Adults

Cardiovascular disease(CVD), the leading cause of death in the world, accounts for 30% of deaths globally. In China, the burden of major CVDs(Coronary Heart Disease(CHD) and stroke), as the leading causes of death and disability, has increased from 1990 to 2010, and CVD deaths resulted in a 4.79-year life expectancy loss in the Chinese population. Hypertension is the main risk factor for CVD mortality, causing more than 7 million deaths worldwide every year. Reducing the burden of diseases associated with hypertension has been identified as a public health priority in the world as well as in China.Consistent with the World Health Organization conventions(1999) and the seventh Joint National Commission guidelines(JNC7), hypertension was defined as a SBP/DBP ≥140/90 mm Hg or current use of antihypertensive medication.Because hypertension is associated with wide phenotypic variability, it can be divided into the following subtypes: isolated systolic hypertension(ISH), isolated diastolic hypertension(IDH), and systolicdiastolic hypertension(SDH). These subtypes may provide important information concerning the causation of hemodynamic and/or structural abnormalities that contribute to hypertension. We were unable to distinguish between ISH, IDH or SDH in incident cases taking antihypertensive medication because their original BP values were unknown, so we classified “current use of antihypertensive medication(MED)” into a specific group. ISH is associated with increased large artery stiffness, which is more common in the elderly, and age, BMI and smoking are significant independent risk factors of ISH. However, the development of IDH and SDH is associated with increased peripheral vascular resistance, which is more prevalent among young adults, and IDH mainly affected by body mass index(BMI).Many cross-sectional studies have reported the prevalence of hypertension. Globally, the overall prevalence in adults ≥25 years of age was 40% in 2008, with the highest being 46% in Africa. The prevalence increased from 24.0% in 1988-1991 to 33.5% in 2005-2008 in American adults. Similarly, several cross-sectional studies have reported the prevalence of hypertension in Chinese adults. The prevalence was reported as 14.5% in 1991 to 34% in 2012. Based on data from the China Health and Nutrition Survey(CHNS), the prevalence has increased from 14.5% in 1991 to 21.4% in 2009.In contrast, longitudinal studies of incident hypertension in large populations have been relatively scarce. In most of these studies, the cumulative incidence rate(CIR, %) was calculated as a measurement indicator of incident hypertension, which was expressed as the percentage of incident cases in a fixed cohort. Average annual CIRs of hypertension ranged from 1.29% to 4.53% in Americans, depending on age, period, gender, ethnicity, and body size of the population. However, so far, few studies have calculated incident hypertension in large cohort studies in China. Over a mean of 8.2 years of follow-up among 10,525 individuals, the CIR of hypertension was 28.9% of men and 26.9% of women, meaning that the average annual CIR was 3.61% in men and 3.36% in women from 1991 to 1999. Based on data from CHNS, the CIR was 26.8% in the CHNS from 1991-2009 and 15.9% in the CHNS from 2000-2004, indicating that the average annual CIR ranged from 2.23% to 3.98% in Chinese adults.However, previous studies using the incidence rate(IR, per 100 personyears) as an indicator for hypertension in long cohort have been relatively rare. There are two reports that have shown that IRs range from 1.8 to 7.4 in Americans. Over a mean of 3.23 years of follow-up among 3,357 individuals in Taiwan, the IR of hypertension was 2.9 in 1994-1997. Based on data from CHNS, only one study to date has reported that the IR of hypertension increased from 2.9 per 100 person-years in CHNS 1991-1997 to 5.3 in 2004-2009. The above incidence of hypertension is inconsistent and could not represent the reality of incident hypertension in the large-scale longitudinal cohort study. The main drawback is the confounding effect of age on the prevalence, since the average age in a cohort will be increasing during the follow-up resulting in a higher prevalence rate even when the age-specific incidence remain stable. To overcome this weakness and considering the CHNS is a dynamic cohort design, we used IR as an indicator in this study. In part one, we calculated the crude prevalence of hypertension subtypes stratified by age and BMI to estimate the age-specific effect of BMI on hypertension in CHNS 2011. In part two, to further understand these aspects of hypertension in Chinese adults, we present a comprehensive analysis of the trends of the prevalence and proportion of hypertension subtypes among the Chinese population using data obtained from CHNS 1991-2011. In part three, we sought to investigate the IR of hypertension and subtypes according to the number of person-years of follow-up utilizing a dynamic cohort study from the CHNS from 1989-2011. More importantly, because elevated body weight is the important modifiable risk factor for hypertension, we further calculated the population attributable risk percent(PAR%) to quantify the contribution of body weight to developing incident hypertension and clarified the age-specific effect of BMI on incident hypertension and subtypes in the dynamic cohort over 22 years. Part one: Prevalence of hypertension Subtypes in 2011 among Chinese AdultsObjectives:We calculated the crude prevalence of hypertension subtypes stratified by age and BMI to estimate the age-specific effect of BMI on hypertension in CHNS 2011.Methods:This study focused on adults aged 18 years or older in 2011. To limit biases caused by pre-existing factors, participants who had been diagnosed with pregnancy or lactating and participants with missing information on systolic blood pressure(SBP) or diastolic blood pressure(DBP) or extreme or implausible blood pressure(BP) values(SBP-DBP <10 mm Hg) were excluded, and participants with missing information on height, weight, extreme or implausible height(<120.0 cm) or BMI(BMI <15.0 kg/m2 or >40.0 kg/m2) values were excluded. Analyses were stratified by gender, age and BMI. The prevalence of ISH, IDH and SDH together with the use of antihypertensive medication from the most recent data(the CHNS of 2011) were compared using the chi square test between males and females as well as a comparison of different age groups. Statistical analysis was performed using SPSS software for Windows version 13.0. The statistical significance was determined as a two-tailed P< 0.05.Results:Normotensive participants(n=12,364) at baseline were included. A total of 3,477 cases of hypertension were documented(men and women were 5,808 and 6,559, respectively). According to CHNS 2011, 28.1%(95% CI, 27.3%-28.9%) of the Chinese adults were hypertensive. The prevalence was significantly greater for males compared to females(30.2%, 95% CI,29.0%-31.3% versus 26.3%,95% CI,25.3%-27.4%; 2X =22.6,P <0.001). The subtype-specific prevalence of hypertension was 4.77%(95% CI, 4.40%-5.15%) of ISH, 4.63%(95% CI, 4.26%-5.00%) of IDH, 5.38%(95% CI, 4.98%-5.78%) of SDH and 13.4%(95% CI, 12.8%-13.9%) of the current use of antihypertensive medication. The prevalence of hypertension in 2011 increased with age; with the highest prevalence being 47.4%(95% CI, 45.1%-49.8%) and 49.6%(95% CI, 47.6%-52.1%) in the age group of ≥60 years in males and females. Similar increasing trends were observed in the ISH, SDH and the use of antihypertensive medications. However, the highest prevalence of IDH was 7.39%(95% CI, 6.41%-8.34%) and 4.40%(95% CI, 3.68%-5.13%) in the age group of 40-59 years in males and females, respectively. The prevalence of hypertension subtypes also increased gradually with BMI. To further clarify the effects of BMI on age-specific prevalence of hypertension, the prevalence in the group of those aged ≥60 and a BMI <20(30.6%, 95% CI, 26.3%-34.9%) was similar to the group of those aged 40-59 and a BMI of 26-27(33.5%, 95% CI, 30.5%-36.5%), suggesting that the effect of increasing 6-8 kg/m2 on the risk of hypertension could be equivalent to that of increasing age by twenty years.Conclusions:According to CHNS 2011, 28.1% of the Chinese adults were hypertensive, with 13.4% of the current use of antihypertensive medication. The effect of increasing 6-8 kg/m2 on the risk of hypertension could be equivalent to that of increasing age by twenty years. Part two: Trends of prevalence of hypertension Subtypes from 1991-2011 among Chinese AdultsObjectives:The prevalence and trends of hypertension subtypes among Chinese adults are still unknown. To further understand these aspects of hypertension in Chinese adults, we present a comprehensive analysis of the trends of the prevalence and proportion of hypertension subtypes among the Chinese population using data obtained from CHNS 1991-2011.Methods:This study focused on adults aged 18 years or older in each survey year. To limit biases caused by pre-existing factors, participants who had been diagnosed with pregnancy or lactating and participants with missing information on systolic blood pressure(SBP) or diastolic blood pressure(DBP) or extreme or implausible blood pressure(BP) values(SBP-DBP <10 mm Hg) were excluded, and participants with missing information on height, weight, extreme or implausible height(<120.0 cm) or BMI(BMI <15.0 kg/m2 or >40.0 kg/m2) values were excluded. Taking into account unequal probabilities of selection, the values of hypertension and subtypes were adjusted by direct method to the 2010 census of the Chinese adults using the corresponding age groups. Analyses were stratified by gender, age and BMI. The age-adjusted prevalence estimates of ISH, IDH and SDH together with the use of antihypertensive medication were compared using the chi square test between males and females as well as a comparison of different age groups. Trends in the age-adjusted prevalence of hypertension and subtypes among participants and trends of the proportion of hypertension subtypes from 1991 to 2011 were assessed by using linear-by-linear trend testing. Statistical analysis was performed using SPSS software for Windows version 13.0. The statistical significance was determined as a two-tailed P <0.05.Results:Compared with 1991, the prevalence increased from 15.6% to 20.9% for hypertension(P<0.001) and from 3.04% to 3.30% for isolated systolic hypertension(P<0.001); However, the prevalence decreased from 4.77% to 4.44% for isolated diastolic hypertension(P =0.023) and from from 5.27% to 4.11% for systolic-diastolic hypertension(P <0.001). Consistent with these findings, the percentage of current use of antihypertensive medication increased from 2.55% to 9.01%, which accounted for approximately 43.1% of the total number of cases in 2011. Importantly, only 36.9%(equivalent to 17.5% of the total number of hypertensive people) of cases of current use of antihypertensive medication were adequately controlled.Conclusions:Both the prevalence of hypertension and the percentage of current use of antihypertensive medication significantly increased from 1991 to 2011. Compared with 1991, the prevalence increased from 15.6% to 20.9% for hypertension. The percentage of current use of antihypertensive medication increased from 2.55% to 9.01% Part three: Joint effects of age and body mass index on the incidence of hypertension subtypes in the china health and nutrition survey: a cohort study over 22 yearsObjectives:We investigated the Incidence rates(IRs, per 100 person-years) of hypertension subtypes utilizing a dynamic cohort study from the China Health and Nutrition Survey(CHNS) 1989-2011. Furthermore, we calculated adjusted relative risks(RRs) and population attributable risk percent(PAR%) of BMI for hypertension, and clarified the age-specific effect of BMI on incident hypertension subtypes. Stratified analyses and Cox proportional hazards models were performed.Methods:We utilized data from the CHNS 1989-2011, a Chinese cohort using multistage random cluster sampling over a 22-year period. To limit biases caused by pre-existing factors, participants who had been diagnosed with pregnancy or lactating and participants with missing information on systolic blood pressure(SBP) or diastolic blood pressure(DBP) or extreme or implausible blood pressure(BP) values(SBP-DBP <10 mm Hg) were excluded, and participants with missing information on height, weight, extreme or implausible height(<120.0 cm) or BMI(BMI <15.0 kg/m2 or >40.0 kg/m2) values were excluded. Stratified analyses were performed to calculate the incidence rates(IRs) and examine the relationship between age, baseline BMI, and joint risks for hypertension and subtypes. Trends of incident hypertension(P for trend) with classifications of age or BMI were assessed using Cox proportional hazards models. Using the ideal BMI(BMI <22 kg/m2) as the referent, we calculated the adjusted relative risks(RRs) of BMI for hypertension by Cox models to control for covariates, such as age, region, ever smoking, alcohol intake, and we used the attributable risk percent(AR%) to reflect BMI as risk factor for developing hypertension. Further, we calculated the population attributable risk percent(PAR %) to quantify the contribution of BMI to developing incident hypertension. We calculated the adjusted relative risks(RRs) of the age-specific effect of BMI on incident hypertension and subtypes by Cox models to control for covariates, such as age, region, ever smoking, alcohol intake; for each analysis, the lowest IR was used as the referent.All statistical tests were performed using SPSS statistical software. Statistical significance was set at a two-tailed P ≤0.05.Results:Normotensive participants(n =53,028) at baseline were included, with mean age was 41.7(95% CI, 41.6-41.7) years old. Men and women were 24,941(47.0%) and 28,087(53.0%), respectively. During a total of 118,694 person years(average was 6.38 years) of follow-up, a total of 5,208 incident cases of hypertension were documented. In this dynamic cohort, the crude IR of hypertension was 4.4(95% CI, 4.3-4.5) per 100 person-years over the 22 years, with an IR of 5.0(95% CI, 4.8-5.1) in men and 3.9(95% CI, 3.7-4.0) in women(P <0.001), respectively. The IR increased gradually with age from 1.5(95% CI, 1.4-1.6) in those aged 18-34 years to 11.3(95% CI, 10.7-12.0) in those aged ≥65 years(Ptrend <0.001). The IR also increased gradually with BMI from 3.0(95% CI, 2.9-3.1) in those with BMI <22 to 9.9(95% CI, 9.1-10.6) in those with BMI ≥28(Ptrend <0.001). Compared with those with BMI <22 kg/m2, the RR of hypertension was 3.13(95% CI, 2.84-3.45) in the group with BMI ≥28 kg/m2, and the PAR% of BMI in Chinese population was 32%(95% CI, 29-34%). Similar trends were observed in all age and BMI groups for both isolated systolic hypertension and systolic-diastolic hypertension, which were mainly affected by age. In contrast, the peak IR of isolated diastolic hypertension was observed in participants aged 30-49 years with higher BMIs.Conclusions:The IRs of hypertension were 4.4(95% CI, 4.3-4.5). The PAR% of elevated body weight for hypertension was 32% in Chinese population. After stratification by age and BMI, incident isolated diastolic hypertension was mainly influenced by BMI.