Risk factors for cardiovascular disease from a population-based screening study in Tianjin, China: a cohort study of 36,215 residents

Introduction

Cardiovascular disease (CVD), sometimes called the “silent disease”, is an ischemic or hemorrhagic disorder of the heart and systemic tissues (1). CVD is caused by bloody lesions and, with no obvious clinical symptoms, is characterized by the secretive, progressive, and systemic manner in which it inflicts damage on the body. CVD is one of the most serious threats to human health worldwide today, especially for middle-aged and older people over the age of 50 (2-5), and its morbidity and mortality have surpassed those of cancer. By 2030, nearly 23.6 million people will die of CVD every year, with only heart disease and stroke causing more fatalities (5).

In China, there are currently 290 million patients with CVD, but with the influence of population increase and aging, the number of patients with CVD is expected to increase by more than 50% by 2030 (6). In recent years, CVD has accounted for 40% of deaths in China, with about 2.6 million people dying from CVD each year (7). This has seen CVD claim its place as the top cause of death and top threat to health in China. Furthermore, the average age of onset of CVD shows a downward trend (8), with more people developing the disease at a younger age. The high incidence of CVD and its impact on quality of life have brought a heavy economic and psychological burden to society, families, and the individuals who suffer with the disease (9).

CVDs include a range of conditions, such as coronary heart disease (heart attack), cerebrovascular disease (stroke), peripheral vascular disease, rheumatic heart disease, and cardiomyopathy. The majority (80%) of patients with CVD are died from heart disease and strokes. The occurrence of CVD is the result of long-term interaction between various adverse factors. Hypertension, diabetes, dyslipidemia, smoking, and obesity are currently recognized as the five major risk factors for CVD (10-12). Related studies have shown that the above-mentioned CVD risk factors have increased in recent decades among the Chinese population, and the accumulation of multiple risk factors is more likely to increase the risk of CVD (13,14). There is evidence that shows that the prevention of risk factors and early screening and diagnosis can greatly reduce the morbidity and mortality of CVD (15).

This study set out to establish a better understanding of CVD risk factors among residents of Tianjin, China, and to provide new insight into the prevention of CVD. This will enable us to effectively control the risk factors of CVD and reduce occurrence and development of the disease in the future.

Methods

Data sources

The data were collected from participants of the Early Screening and Comprehensive Intervention Program for High Risk Population of Cardiovascular Disease in Tianjin on July 31, 2017. A total of 36,215 participants were recruited including 25,494 classified as non-high risk and 10,721 classified as high risk. The criteria for assessing high-risk CVD were CVD history, hypertension, dyslipidemia, WHO risk assessment, and a risk of ≥20% in special subjects.

Data analysis

The information of each participant included personal information, personal and family medical history, biochemical indicators and physical indicators. Personal information included age (one level every five years), gender, ethnicity, household registration, marital status, education, family income, recent smoking status, and drinking status in the past year. Personal medical history took into account hypertension, diabetes, myocardial infarction, stroke, chronic obstructive pulmonary disease, dyslipidemia, bypass surgery, or percutaneous coronary intervention. Family medical history referred to: the number of people in the participant’s family aged >90; the number of family members who had died of myocardial infarction, stroke, cancer, or sudden death; and family members who had received heart bypass surgery, stent implantation, valve replacement, radiofrequency ablation, implantation of automatic defibrillator, heart transplantation, or surgery for congenital heart disease. Biochemical indicators contain cholesterol, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), blood glucose, triglyceride, proteinuria, ketone bodies, and occult blood. Physical indicators included body mass index (BMI), heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), and waist circumference.

Statistical analysis

According to the data type, Pearson’s chi-squared test, with and without Yates’s continuity correction, and Fisher’s exact test were used to analyze the relationship between personal information, personal and family medical history, biochemical and physical indicators, and the relationship between CVD risk and these indicators. The correlation between the indicators was expressed using the number of column connections, and the hierarchical data of two independent samples were analyzed using the Mann-Whitney test.

Logistic regression analysis was conducted to explore related indicators in four categories: personal information, family medical history, biochemical indicators, and physical indicators. Variables were screened using a conditional parameter estimation likelihood ratio test, with an inclusion criterion of P<0.05 and a rejection criterion of P>0.1.

All analyses were performed using SPSS 21.0 (IBM Corporation, America) and R 3.4.4 (the Institute for Statistics and Mathematics of WU, Austria). The network map was drawn using Cytoscape. Statistical significance was considered to exist when P<0.05.

Results

Personal information

There were significant differences found in age, gender, marital status, education level, household income, and smoking and drinking habits between the non-high-risk group and high-risk group (P<0.001), and all the contingency coefficients were within 0.1 [except for age (0.262)], which indicated a certain relationship between these factors and CVD (Table 1). There were no significant differences between ethnicity or household registration and CVD risk (Table 1).

Table 1 The relationship between cardiovascular disease (CVD) risk and personal information
Full table

Personal and family medical history

With the exception of chronic obstructive pulmonary disease, all other personal medical history indicators were associated with CVD risk, and had significant difference (P<0.001). Among these indicators, hypertension or stroke had a contingency coefficient with CVD risk of more than 0.3 (Table 2). For diabetes, myocardial infarction, dyslipidemia, and percutaneous coronary intervention the contingency coefficient with CVD risk reached 0.15–0.30 (Table 2). Patients whose relatives who had undergone heart transplant and valve replacement surgery were also associated with CVD risk. Of the other family-related indicators, the number of relatives aged >90 (Figure 1A), and relatives with myocardial infarction, stroke, and cancer, were associated with CVD risk with contingency coefficients higher than 0.15 (Table 3).

Table 2 The relationship between cardiovascular disease (CVD) risk and personal disease history
Full table

Figure 1 Density plots of high risk of CVD in all participants. Data are shown stratified by the number of family members over 90 years of age (A), the number of relatives with myocardial infarction (B), cholesterol (C), blood glucose (D), systolic blood pressure (E) and diastolic blood pressure (F). The density means estimated probability risk of CVD. The area under the curve is 1.

Table 3 The relationship between cardiovascular disease (CVD) risk and disease history of relatives
Full table

Biochemical index and physical fitness index

All the biochemical indicators apart from ketone bodies were significantly associated with CVD risk (Figure 1B). The contingency coefficient of cholesterol (Figure 1C), LDL-C, and blood glucose (Figure 1D) and the risk of CVD reached more than 0.2 (Table 4). The contingency coefficient between other indicators and CVD risk were low, but there were significant differences between the high-risk and non-high-risk groups (P<0.001). Among the physical indicators, the contingency coefficient of SBP and DBP and CVD risk in the high-risk and non-high-risk groups were 0.339 and 0.257, respectively, and the P value was less than 0.001 (Table 4, Figure 1E,F). There were meaningful differences in BMI, waist, and heart rate between the high-risk and non-high-risk groups, but the contingency coefficient with CVD risk was not high (Table 4).

Table 4 The relationship between cardiovascular disease (CVD) risk and biochemical index
Full table

Multi-factor logistic regression analysis

Our logistic regression model comprised 12 indicators with a predictive power of 78.6%. According to the results of regression analysis, the risk of CVD increased by 0.296 for every 5-year increase in age. Compared with patients with SBP >140 mmHg, the risk of CVD was only 0.344 and 0.310 in patients with SBP <130 and 130–140 mmHg, respectively. Compared with subjects with DBP >90 mmHg, subjects with DBP <60 mmHg and between 60 and 90 mmHg had only 0.268 and 0.320 risk of CVD, respectively. For every additional person in a subject’s family who was >90 years old or had suffered a stroke, the risk of CVD was 2.69 times or 2.307 times higher, respectively, than that of normal people (Table 5).

Table 5 Multi-factor Logistic regression for cardiovascular disease (CVD) risk
Full table

Decision tree model analysis

Subjects with incomplete information were excluded, and the remaining 32,262 cases were randomly divided into two sets: 70% in the training set and 30% in the validation set. Firstly, focusing on the training set, we selected meaningful indicators (including personal information, family medical history, biochemical indicators, and physical indicators) to construct decision trees. The decision tree model had 17 nodes and 8 endpoints with a depth of 3 (Figure 2). In the decision tree, the first layer was SBP, indicating it had the strongest association with the risk of CVD. Participants with SBP >140 mmHg had higher incidence of CVD. In addition, having more than 2 family members aged >90 years had the most significant impact on the risk of CVD. When the SBP >140 mmHg and there were 0 or 1 family members >90 years of age, the participants with DBP >90 mmHg had a higher risk of CVD than those with <90 mmHg. Moreover, participants who had 2 or 3 family members >90 years old were part of high-risk group (Figure 2). The accuracy of the decision tree model on the training and validation sets was 77.4% and 77.3%, respectively.

Figure 2 Tree diagram generated by decision tree model.

Correlation analysis among factors

By analyzing the correlations among the various indicators, we filtered out the correlations with relative coefficient >0.2 to construct a network map. In the network, a correlation was identified between hypertension and seven indicators, including SBP, DBP, and BMI. Hypertension and SBP had the largest correlation. SBP had a correlation with six indicators, while BMI, cholesterol, and blood glucose were associated with five other indicators (Figure 3).

Figure 3 Correlation network between different indicators. Different colored lines indicate different correlation. The diamond indicates that the indicator had a correlation with more than five indicators.

Discussion

The characteristics of CVD risk factors differ from region to region according to variations in diet and lifestyle. A large number of studies have analyzed the risk factors for CVD in different regions of China. This study provided a unique opportunity to analyze in detail the CVD risk factors to public health in Tianjin, China. In the present research, we focused on the correlation of various factors with CVD degrees, and displayed it through a network diagram. In this network, SBP, DBP, BMI, age, diabetes, waist circumference, and hypertension were all associated with CVD risk. BMI, cholesterol, and blood glucose were associated with five other indicators. These results allow us to understand the relationship between CVD and its risk factors, especially family disease history and physical indicators, and this is conducive to the design of reasonable strategies to control the morbidity of CVD.

A lot of research has been done on the risk factors for CVD. Yu et al. (16) studied CVD-related prevalence and demographic-related risk factors in Jilin Province, and pointed out that people who are elderly, or who have low-income or low-education should be targeted in the prevention of CVD. Based on the prevalence and risk factors of CVD in rural communities in Fangshan District of Beijing, He et al. (17) forecast that high-risk factors of CVD and population aging might become public health problems in developing rural areas. Xu et al. (18) found that hypertension, diabetes, overweight/obesity, dyslipidemia, and current smoking were major CVD risk factors in the Tibetan population. However, little exploration has been carried out of the characteristics of CVD risk factors in Tianjin.

This study analyzed the statistical data of the Early Screening and Comprehensive Intervention Program for High Risk Population of Cardiovascular Disease, conducted by the National Cardiovascular Center in Tianjin. SBP, number of relatives over 90 years old, hypertension, and BMI were the major CVD risk factors in Tianjin residents. The predictive ability of the logistic regression model was 78.6%, indicating that this study has certain significance for guiding the prevention and intervention of CVD in Tianjin.

CVD risk factors can be divided into genetic and environmental risk factors, with the latter closely related to lifestyle and of greater importance. Smoking, obesity, hypertension, diabetes, unhealthy diet, and lack of physical activity are environmental risk factors, and eliminating or changing related behaviors can help to prevent CVD.

Hypertension is the most crucial and independent risk factor for CVD (19), and is currently one of the most common diseases in China (20). Hypertension can easily cause atherosclerosis, further damage to areas including the heart, cerebrovascular system, kidneys, and aorta, and the incidence of coronary heart disease can be enhanced (20). This study found that people with SBP >140 mmHg or DBP >90 mmHg showed an increased risk of CVD. An increased systolic and DBP heighten the risk of hypertension, which may further trigger CVD.

In addition, family history of CVD is a hereditary, unchangeable risk factor. Family history of CVD is a recognized risk factor, and multiple prospective studies have demonstrated consistent and independent associations between family history and CVD (21). A study has shown that family history of early coronary heart disease (CHD) is associated with a sustained increase in the risk of CHD and CVD death during long-term follow-up, resulting in a significant increase in lifetime risk assessment. A study by Ranthe et al. (22) concluded that the family history of early-onset CVD death is consistently and markedly associated with the risk of early-onset CVD, which indicates a genetic heart disease susceptibility. In our study, we demonstrated that participants who had a relative older than 90 or a stroke patient member in their family had a 2.069-fold and 2.307-fold increased risk of CVD, respectively. Additionally, SBP, DBP, the number of relatives aged over 90, and stroke patients in the family constituted the decision tree model. The accuracy of the decision tree model on the training set and test set was 77.4% and 77.3%, respectively. These four indicators in the model may be an important component of CVD screening and diagnosis.

Typically, each CVD patient has multiple risk factors. With societal advancements and improved living standards, everyone has increased exposure to CVD risk factors. The accumulation of multiple CVD risk factors in the same individual poses a serious issue. Previous studies have found that the relative risks of coronary heart disease or stroke associated with 1, 2, 3, and ≥4 risk factors were 1.6 or 1.4, 2.2 or 1.9, 3.1 or 2.3, and 5.0 or 4.3, respectively (23). Reported by Yang et al. (23) compared with patients without risk factors, patients with 1, 2, 3 or ≥4 risk factors had an odds ratio of 2.36, 4.24, 4.88, and 7.22 for CVD, respectively. Many studies have revealed that the occurrence of CVD is the result of long-term interactions of multiple adverse factors. Our study considered the relationship between various risk factors in the CVD prevention and screening process, which is of great significance for the prevention of CVD and the improvement of public health awareness.

Conclusions

In conclusion, this study provided a scientific basis for the development of CVD prevention and control measures and strategies. By designing ongoing individualized coaching and support, better long-term clinical improvements in patients with CVD can be achieved.

Acknowledgments

We would like to thank all the members of our research group for their enthusiastic participation in this study.

Funding: This work was funded by the Program of Tianjin Science and Technology Plan from Tianjin Science and Technology Commission (15ZXHLSY00320). The Tianjin Science and Technology Commission and its partners had no role in the study design, data collection, analysis, or interpretation. The research was conducted independently of the funders, and the views expressed in this paper are those of the authors and not necessarily those of the Tianjin Science and Technology Commission or other government departments. The final version of the paper and ultimate decision to submit for publication was determined by the authors.

Footnote

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/atm.2020.03.139). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The data for the research was obtained from an existing database containing details held by the Early Screening and Comprehensive Intervention Program for High Risk Population of Cardiovascular Disease.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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