The cross-sectional study obtained regional prevalence of CVDs and associated risk factors among representative population of Nanjing adults. Participants with CVDs had higher levels of BMI, BP, FPG, TG, TC, LDL-C and a lower HDL-C level than subjects without CVDs. We also found that five modifiable risk factors could be associated with CVD events, and risk factors clustering had possibly increase gradually risks of self-reported CHD or stroke regardless of genders.
The overall weighted prevalence of self-reported CHD and stroke in the present study was higher than that in the nationwide population , but lower than in the United States . A nationally representative sample of 46,239 adults aged ≥ 20 years from the 2007–2008 China National Diabetes and Metabolic Disorders Study indicated that the standardized prevalence of self-reported CHD and stroke was 0.6%, 0.8%, respectively . In 2008–2011 multicenter prospective population-based Hispanic Community Health Study , the overall prevalence of CHD and stroke among persons aged 18 to 74 years was 4.2% and 2.0% for men, and 2.4% and 1.2% for women, respectively.
Sino-Monitoring Trends and Determinants in Cardiovascular Disease (Sino-MONICA) project [32, 33], the China Multicenter Collaborative Study conducted from 1987 to 1993, indicated that stroke incidence and mortality were higher compared with western countries, but the same rates for CHD were lower than western countries. The pattern of CVDs occurrence in China was the high stroke events combined with low CHD events, which was similar to other eastern Asian countries (Korea, Japan, Singapore and Thailand). The epidemic pattern was thought to be associated with higher BP levels and lower serum TC levels as seen in Sino-MONICA study .
In previous studies [6, 32, 33], the morbidity and mortality of CVDs in China was significantly higher in northern and rural areas than southern and urban counterparts, respectively. The geographic variations in CVD mortality and incidence may attribute to the north-south differences in CVD risk factor profiles. Dietary preferences of salt or other spices in northern China were related to the higher prevalence of hypertension. It has been estimated that 1.7 million annual cardiovascular deaths have been due to excess salt/sodium intake (more than 5 g per day) globally in 2010 . High salt consumption is related to raised blood pressure and increased risk of CVD events. Furthermore, the cold weather may limit outdoor physical activity, enhance fat reservation, and consequently increase the risk of obesity and metabolic abnormalities in northern regions. Additionally, increasing urbanization, limited medical resources and imperfect healthcare system may be responsible for the higher prevalence of CVDs and its risk factors in rural regions.
Our findings revealed that higher levels of BMI, SBP and FPG could be associated with increased risks of self-reported CHD and stroke, whereas higher level of HDL-C could be related to lower risks of CHD. In addition, hypertension, diabetes and dyslipidemia had possibly positively associations with the risk of CVDs, which was consistent with previous observations [7–12]. In China, the five leading risk factors were high blood pressure, tobacco smoking, high sodium intake, high FPG and high BMI as reported the 2013 Global Burden of Disease Study . Although the prevalence of CVD risk factors has decreased in economically developed countries, the corresponding prevalence has increased in economically developing countries, including China. Hypertension, as one of the most important risk factor for CVDs, has been found to be highly prevalent in China currently. According to the 2002 the China National Nutrition and Health Survey (NNHS) , the prevalence of hypertension among Chinese adults aged over 18 years was 18.8%, and increased to 25.2% in the 2015 report of China National Nutrition and Chronic Disease Survey (NNCDS) , which was close to our finding (25.0%). Based on data from 2013 report on chronic disease risk factor surveillance in China , the awareness (40.9%), treatment (32.5%) and control (9.7%) of hypertension were still suboptimal. A reduction of 10 mmHg in SBP was connected with a 22% reduction in CHD and 41% reduction in stroke in randomized trials . The overall prevalence of diabetes was estimated to be 11.6% in the Chinese adult aged 18 years and older from the 2010 China Chronic Disease and Risk Factor Surveillance , whereas the rate was 2.6% in 2002 . The prevalence of dyslipidemia (34.0%) among Chinese adults was high, but rates of awareness (31.0%), treatment (19.5%) and control (8.9%) of dyslipidemia were low in the general Chinese population aged more than 18 years between 2007 and 2010 . The 2015 NNCDS reported  that the prevalence of overweight and obesity reached 30.1% and 11.9%, whereas the corresponding value was 17.6% and 5.6% in the 2002 NNHS , respectively. In the 2010 Global Adult Tobacco Survey , the overall smoking rate among Chinese adults over 15 years of age was 28.1% (52.9% of men and 2.4% of women). The rate of diabetes, dyslipidemia, overweight or obesity, current smoking in the present study was lower than the national levels mentioned above [36, 39–41].
Our finding also indicated that the risks for self-reported CHD and stroke were likely to increase substantially with each additional risk factor, in line with other previous reports [13, 42, 43]. Numerous studies [12, 42, 43] have confirmed that CVD incidence and all-cause mortality increased markedly with risk factor clustering. Data from the First National Health and Nutrition Examination Surveys Epidemiologic Follow-up Study , the adjusted relative risks of CHD in adults with one, two, three, four or more risk factors were 1.6, 2.2, 3.1 and 5.0 during 21 years of follow-up, respectively, compared to those with no risk factors. The adjusted relative risks of stroke associated with the same risk levels were 1.4, 1.9, 2.3 and 4.3, respectively. After 26 years of follow-up, favorable cardiovascular risk profile in middle age was associated with better quality of life and lower risk of CVDs in older age from the Chicago Heart Association Detection Project in Industry . By applying the recalibrated Framingham risk function to the Inter Asia study , the 10-year CHD risk increased 0.2%, 1.7%, 3.2% and 10.4%, respectively, for Chinese adults with none, one, two and at least three of risk factors. A prospective cohort study  carried out in Chinese population aged 35–64 years showed that the incidence rate of CVDs increased significantly with the number of risk factor clustering, and found that there were a significant synergistic effects between each CVD risk factor.
Proper management including lifestyle modification or medical treatment may be the most effective strategy in reduction the pervasive CVDs burden under the supervision of the government. At the national health conference in 2016, China government ensured that health became an explicit national political priority with the approval of the Healthy China 2030 Planning Outline by China’s Central Party Committee and the State Council. This document was the first general guideline for the promotion of healthy lifestyles and physical fitness at the national level, which stressed that the health should be combined into all major policies.
First, China has launched national fitness program vigorously and promoted comprehensive development of both recreational and competitive sports in recent years. Sufficient physical activity can reduce the risk of cancer, diabetes, CVDs and all-cause mortality . To meet the requirement of growing health, government has designated 8th August as “national fitness day” since 2009. In 2013, only 15% of Chinese residents aged over 18 years took regular exercise (participating moderate or vigorous intensive PA at least 10 minutes three days per week) in leisure time . The percentage of regular physical activity among Chinese adults will increase to 40% in 2030. Second, Chinese adults are recommended to adopt healthy dietary pattern, with high intake of whole grains, fresh vegetables and fruits, dairy products, soy foods, poultry meat, fish and shrimp, unsaturated cooking oil, and low intake of processed meat, red meat, fried foods, western fast foods, snacks and desserts . Meanwhile, reduction in salt intake is also an essential part of CVDs management strategy. The average daily intake of salt in 2012 was 10.5 g per person , which was much higher than the recommended level by 2016 dietary guidelines for Chinese residents (lee than 6 g/d). The daily intake of salt in 2030 will be reduced relatively by 20% compared to 2012 national level. Third, China has tightened rules on smoking in public places. The rule that smoking is banned in indoor public places has been in force since 1 May 2011. The Ministry of Education and Ministry of Health jointly issued guidelines with regard to the further enhancement of tobacco control in schools in June 2011. All indoor and outdoor areas of kindergartens, primary and secondary schools, including vocational schools, should be smoke-free. Additionally, the overall prevalence of smoking among Chinese adults aged over 15 years will reduce to 20.0% in 2025. Fourth, with the increasing prevalence of hypertension, diabetes, dyslipidemia and obesity in China, better management of CVD risk factors are in urgently needed. Due to the poor public awareness, treatment and control of risk factors, more education and training (e.g., increased government investment), the application of evidence-based screening, prevention and therapies should be encouraged in China .
Several limitations of our study should be noted. Firstly, this study was a single-center, observational study. The associations between CVD risk factors and CVD events should be evaluated in the future prospective studies from multiply centers. Secondly, the information on smoking status, CHD and stroke status was based on self-reported data, which could be subject to reporting bias and may underestimate the prevalence of CVDs. To ensure the reliability of these self-reported measures, the survey respondents with a history of CHD or stroke were asked to provide investigators with their medical records in tertiary hospitals. Thirdly, CVD risk factors were involved modifiable and non-modifiable risk factors, only five major modifiable factors were considered in the present study. However, other relative risk factors (older age, men, lower levels of SES, having family history of CVDs, physical inactivity and unhealthy dietary habits) were taken into account to enter into the logistic regression analyses. Finally, cross-sectional studies with binary outcomes analyzed by logistic regression are frequent in the epidemiological literature. There is nothing intrinsically wrong with them. However, the ORs can importantly overestimate the prevalence ratio. Therefore, the different alternatives to analyze our data using prevalence ratios instead of ORs can be chosen for the future.
The present study also had several strengths. This was the first study to explore the association of CVD risk factors, their clustering with CVDs among a large representative sample of Nanjing adults. Another strength was that a strict quality control was implemented to ensure the reliability and validity of study data, which suggested that the findings could be cautiously generalized to other population.