To the Editor: The relationship between hypertension duration and the risk of cardiovascular diseases (CVDs) has received considerable attention in recent years.[1-3] A cohort study based on 246,459 Korean adults found a linear dose–response relationship between hypertension duration and stroke.[1] Another cohort study involving 15,472 White and 10,298 Black adults found that the hypertension duration–heart failure relationship was stronger for people with longer hypertension duration, and there was no evidence of race on the relationship.[2] However, previous population-based and observational studies have mainly focused on non-Chinese populations.[1,2] Notably, prospective data from 39,774 coal workers in Chinese Han suggested that the risk of CVDs and stroke increased with increasing hypertension duration, but no associations with myocardial infarction were found.[3] Importantly, to our knowledge, it remains unclear whether ethnicity differentially affects the associations between hypertension duration and CVDs in Chinese individuals.
China is a multiethnic country, the Dong, Miao, and Bouyi ethnic group members in China have all exceeded one million. The comprehensive health status of China ranks in the middle to upper level worldwide; Guizhou Province in Southwest China ranks lower, and ethnic minority areas in this region have relatively few medical resources. Thus, monitoring and prevention of CVDs in Southwest China should be improved.
Is there a potential linear dose–response relationship between hypertension duration and the risk of CVDs? Are there differences in the degree to which hypertension duration affects the risk of CVDs among various ethnicities?
From July 2018 to August 2019, 18,790 participants aged 30 to 79 years were recruited from Guizhou Province, Southwest China, using a multistage, stratified cluster sampling procedure based on the China Multi-Ethnic Cohort Study.[4] Dong, Miao, and Bouyei ethnicities were enrolled in this study. We excluded individuals with incomplete data on hypertension duration (n = 1); the remaining 18,789 participants were included in the final analysis. Details have been described previously and are presented in the Supplementary material, https://links.lww.com/CM9/B366.[4] Ethics approval was obtained from the Sichuan University Medical Ethical Review Board (No. K2016038) and the Research Ethics Committee of the Affiliated Hospital of Guizhou Medical University (No. 2018[094]). All participants signed written informed consent forms before taking part in the study.
We defined hypertension as a combination of previous hypertension diagnosis by a doctor, systolic blood pressure (SBP) ≥140 mmHg, diastolic blood pressure ≥90 mmHg, and/or use of antihypertensive drugs. Hypertensive participants were asked about their age at the first onset. We calculated hypertension duration using the following formula: age of participants − the age of hypertension diagnosis. Hypertension duration was classified as follows: 0 year (reference), >0 to ≤5 years, and >5 years.
The study endpoint was a composite of total CVDs events, including coronary heart disease, stroke, and arrhythmia, which were identified based on self-report questionnaires that asked if people had ever been diagnosed by a doctor. The validity has been verified.[5,6]
The age-standardized prevalence was calculated based on China Census data in 2010. We used multivariable logistic regression models to examine the association of risk of CVDs and hypertension duration among total participants and in the three ethnic groups. Multiadjusted odds ratios (ORs) and 95% confidence intervals (CIs) were reported. Moreover, we performed subgroup analyses stratified by age, sex, and residence. We also performed two sensitivity analyses that excluded current smokers and alcohol consumers (n = 3593) and further excluded people with diabetes, hyperlipidemia, or cancer (n = 1063). As well, we performed a trend test to calculate P for trends using the median value of each exposure factor in multivariable logistic regression models. Additionally, we calculated the multiadjusted ORs and 95% CIs for CVDs per 1-year increase in hypertension duration. An additional analysis was conducted among hypertensive patients and assessed the effect of antihypertensive drugs and hypertension control (based on self-reported data). Potential confounders included age, sex, ethnicity, residence, marital status, education level, annual household income, current tobacco smoking, weekly alcohol consumption, tea consumption, beverage consumption, total energy intake, sleep duration, total physical activity, family history of CVDs, and body mass index, as well as SBP, fasting plasma glucose, total cholesterol, high-density lipoprotein-cholesterol, and serum uric acid levels, except for the stratified variables. All data were analyzed using SAS 9.1 (SAS Inst. Inc., Cary, NC, USA), and figures were plotted using Stata 16.0 (Stata Corp, College Station, TX, USA). Statistical significance was set at P < 0.05 based on two-sided probability.
Supplementary Tables 1–10, https://links.lww.com/CM9/B366 present participant characteristics. Age-standardized CVDs prevalence was 3.18%, 3.02%, and 3.20% among the Dong, Miao, and Bouyei ethnicities, respectively [Supplementary Figure 1, https://links.lww.com/CM9/B366].
A higher CVDs risk was associated with longer hypertension duration in total participants, and the adjusted ORs (95% CIs) were 2.37 (1.87–2.99) and 3.89 (3.14–4.83) for the >0 to ≤5 years and >5 years, respectively, compared with the reference group (P for trend <0.001; Figure 1). The corresponding values were 2.23 (1.55–3.19) and 2.65 (1.86–3.77) among the Dong ethnicity, 1.88 (1.20–2.93) and 4.66 (3.14–6.91) among the Miao ethnicity, and 3.07 (2.01–4.71) and 5.15 (3.48–7.63) among the Bouyei ethnicity, respectively (all P for trend <0.001; Figure 1).
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Figure 1: Multivariable logistic regression analysis on the risk of CVDs according to hypertension duration. CI: Confidence interval; CVDs: Cardiovascular diseases; OR: Odds ratio.
For every 1-year increase in hypertension duration, CVDs risk increased by 5% (OR 1.05 [95% CI, 1.04–1.06]), 3% (1.03 [1.01–1.04]), 7% (1.07 [1.05–1.10]), and 7% (1.07 [1.05–1.10]) for all participants and participants of the Dong, Miao, and Bouyei ethnicities, respectively [Figure 1].
The results of stratified analyses by age, sex, and residence are presented in the Supplementary Tables 11 and 12, https://links.lww.com/CM9/B366. In the sensitivity analyses, the trend of the hypertension duration–CVDs risk relationship remained almost unchanged [Supplementary Table 13, https://links.lww.com/CM9/B366].
When the hypertension duration–CVDs risk association was examined stratified by CHD and stroke, the results were mostly similar to the main analyses [Supplementary Tables 14–16, https://links.lww.com/CM9/B366]. Additionally, the results among hypertensive patients are presented in the Supplementary Tables 17–19, https://links.lww.com/CM9/B366.
As far as we are aware, there is a paucity of data on the association between hypertension duration and CVDs risk among ethnic groups in Chinese individuals. We examined the associations in a population-based study of 18,789 middle-aged and older adults with different ethnicities in China, and we observed positive and linear dose–response relationships between long-term hypertension and CVDs risk. There were ethnic differences in this association.
Our study provided a more comprehensive understanding of the hypertension duration–CVDs risk relationship among different ethnic groups in China. The risk of CVDs was increased in the Dong, Miao, and Bouyi ethnicities (and the risk increased in the same order). Ethnic differences in the hypertension duration–CVDs risk association make it all the more important to prevent the occurrence or development of hypertension in the Bouyi communities and reduce the hypertension-related CVDs risk. In general, these data indicate that managing blood pressure levels early is a crucial strategy for controlling CVDs to achieve a reduction in the incidence of CVDs among different ethnicities. However, whether long-lasting hypertension truly increases CVDs risk needs further exploration.
Available evidence from epidemiological studies on different populations supports the linear association between hypertension duration and CVDs risk. Consistent with previously published articles, our data indicated a linear trend of the relationship among the included ethnicities. Although similar results were observed when analyses were restricted to participants that did not currently smoke or consume alcohol on a weekly basis, interestingly, CVDs risk decreased compared with the main analyses [Supplementary Table 2]. When the analyses excluded people with several chronic diseases, CVDs risk was further reduced. Moreover, the risk reduction was largest among the Bouyei ethnicity, followed by the Miao and Dong ethnicities. Notably, the proportions of individuals that currently smoked and consumed alcohol on a weekly basis were lower in the Bouyei ethnicity compared with the Dong and Miao ethnicities; thus, larger impact of these unhealthy lifestyles on the hypertension duration–CVDs risk relationship and a higher risk of hypertension-related CVDs attributed to shorter hypertension duration were observed in the Bouyei ethnicity. The present findings place more emphasis on the importance of preventing hypertension early in the course of the disease. Additionally, more attention should be given to smokers, consumers of alcohol, and people with chronic diseases; education and awareness efforts should be doubled to urge people to maintain healthy behaviors, promote a healthy living environment, and achieve optimal health.
Some possible explanations that link hypertension duration to CVDs are as follows: First, left ventricular hypertrophy, left atrial enlargement or fibrosis, or diastolic dysfunction could be induced by long-term hypertension and then lead to an increased risk of CVDs. Additionally, damage to the function of the endothelium and smooth muscle in intracerebral arteries as well as accelerated atherosclerosis, which may be caused by high intraluminal pressure, could increase the risk of brain edema, the formation of local thrombi or ischemic lesions, lacunar infarcts, or intracerebral hemorrhages.[7] In addition, collateral circulation could be negatively impacted by increased resistance in the peripheral vasculature, which may be caused by adaptive structural changes in the resistance vessels.[7] Moreover, people with higher blood pressures may have extensive vascular damage and therefore need to maintain adequate end-organ perfusion. The above mentioned possible mechanisms are possible explanations for the hypertension duration–CVDs risk relationship and warrant further study.
Notably, the potential public health implications of these findings should be highlighted. If a longer hypertension duration associates with increased CVDs risk, this highlights the importance of detecting hypertension early and improving the control of blood pressure early in the disease to curb subsequent CVDs epidemics as much as possible. Given the sheer size of China's population, the multiethnic characteristics, and limited awareness of hypertension status, insufficient treatment and control, these recommendations will potentially benefit targeted ethnicity-specific people.
The primary strength of our study is that data on the hypertension duration–CVDs risk relationship for various ethnic groups are limited, especially for data in China, and we investigated the association in different ethnicities in China. Another strength of the study is that we performed trend tests to explore potential dose–response relationships.
Nevertheless, our study has some notable limitations. First, the real impact of long-term hypertension on CVDs risk and the inference of causal association were difficult to make based on the cross-sectional design. More detailed analyses could be performed using longitudinal data from our ongoing cohort study over future years of follow-up years. Second, we aimed to preliminarily assess the association based on available data of this cross-sectional study, hypertension prevalence may be underestimated because data of hypertension duration mainly came from questionnaire, we will combine questionnaire results and data of hypertensive individuals identified during follow-up survey to conduct a more detailed assessment. Third, other CVDs subtypes were not included because the data were unavailable. Fourth, we did not evaluate arrhythmia, or subtypes of CHD and stroke, or analyze hypertension duration by categories, and thus may have found inapplicable results because of the limited sample size. Finally, our analysis may include potentially relevant residual confounders or incomplete adjustments.
In summary, hypertension-attributable risk of CVDs is a major public health challenge. Our data provide additional evidence of the association between hypertension duration and prevalent CVDs among different ethnic groups in China, especially in patients with long-term hypertension. Ethnicity-specific strategies should be formulated and optimized. Positive interventions targeting different ethnicities with hypertension are emphasized. Ameliorating further increase in the epidemic and disease burden of CVDs associated with long-term hypertension requires the combined efforts of health policy-makers, health care providers, the general population, and individuals. If future studies support the findings of this study, it could reinforce the value of our study and have far-reaching consequences for CVDs prevention.
Acknowledgments
The authors gratefully acknowledge all the staffs and participants of The China Multi-Ethnic Cohort Study for their participation and contribution.
Funding
This study was supported by a grant from the National Key Research and Development Program of China (No. 2017YFC0907301).
Conflicts of interest
None.
References
1. Kim T, Yang P, Yu HT, Jang E, Shin H, Kim HY, et al. Effect of hypertension duration and blood pressure level on ischaemic stroke risk in atrial fibrillation: Nationwide data covering the entire Korean population. Eur Heart J 2019;40:809–819. doi: 10.1093/eurheartj/ehy877.
2. Mefford MT, Goyal P, Howard G, Durant RW, Dunlap NE, Safford MM, et al. The association of hypertension, hypertension duration, and control with incident heart failure in black and white adults. J Clin Hypertens 2020;22:857–866. doi: 10.1111/jch.13856.
3. Wang C, Yuan Y, Zheng M, Pan A, Wang M, Zhao M, et al. Association of age of onset of hypertension with cardiovascular diseases and mortality. J Am Coll Cardiol 2020;75:2921–2930. doi: 10.1016/j.jacc.2020.04.038.
4. Zhao X, Hong F, Yin J, Tang W, Zhang G, Liang X, et al. Cohort profile: the China Multi-Ethnic Cohort (CMEC) Study. Int J Epidemiol 2021;50:721–721l. doi: 10.1093/ije/dyaa185.
5. Yang BY, Guo Y, Morawska L, Bloom MS, Markevych I, Heinrich J, et al. Ambient PM1 air pollution and cardiovascular disease prevalence: insights from the 33 Communities Chinese Health Study. Environ Int 2019;123:310–317. doi: 10.1016/j.envint.2018.12.012.
6. Davies NM, Dickson M, Smith GD, van den Berg GJ, Windmeijer F. The causal effects of education on health outcomes in the UK Biobank. Nat Hum Behav 2018;2:117–125. doi: 10.1038/s41562-017-0279-y.
7. Johansson BB. Hypertension mechanisms causing stroke. Clin Exp Pharmacol Physiol 1999;26:563–565. doi: 10.1046/j.1440-1681.1999.03081.x.
