Introduction

Atherosclerotic cardiovascular diseases (ASCVD) account for major disease burdens and mortality worldwide. It is estimated that more than 23 million people will die due to cardiovascular diseases annually by the next decade1. Therefore, preventing cardiovascular disease (CVD) is one of the most promising strategies to avoid further burdens and deaths2. Every version of the CVD primary prevention guidelines has emphasized controlling cardiometabolic risk factors as the most effective strategy in primary prevention3. Administration of statins alongside a healthy lifestyle is a common way to avoid plaque formation and cardiovascular events4. Calculation of cardiovascular risk score is a key step for deciding who is appropriate for preventive interventions like statin therapy5,6. Although these tools cover important well-known cardiometabolic risk factors, there are still other risk factors that could be added to these calculators7. Recent studies showed that the living environment influences the risk of different metabolic syndrome-related diseases such as fatty liver disease and cardiovascular diseases8. Previous reports indicated that while ASCVD mortality and morbidity have been increasing in low-income areas, developed regions have been successful in controlling its deaths and burdens9,10. Poor cholesterol control is one of the main weaknesses in primary prevention of ASCVD among rural people which should be addressed in the following studies11.

On the other hand, other reports showed that living in cities with more air pollution increases the risk of Cardiac events and mortality12. Long-term Breathing in a concomitant environment of urban areas provokes endothelial dysfunction and makes vulnerable plaque in systemic circulation and coronary arteries13. Also, a sedentary lifestyle in urban regions increases the lipid profile imbalance in favor of plaque formation14. Migration to urban areas is a controversial risk factor for cardiovascular events in previous studies15,16. Some evidence supports that living in urban areas ameliorates the cardiovascular risk factor profile more than living in rural areas17. Also, other findings supported that the rural population had more risk factors for cardiovascular diseases18. Different lifestyle and environmental risk factors affect CVD risk and need appropriate policies to decrease the CVD risk.

The Iranian community has seen a significant shift in lifestyle, demographics, and socioeconomic standing in recent years as a result of increased industry and urbanization19. Iran has seen a surge in urban population and the fast growth of cities in recent years20. Considering Iran’s urban population in 2006, the country’s urbanization rate was 68.46%, showing an upward trend when compared to 1955 (31.67%). Furthermore, it reached 71.37% in 2011. By 2050, 78.2% of people will live in urban areas, according to UN statistics, which suggests that this tendency will continue in the years to come21,22. Migration from rural to urban areas, which occurs as a result of the income disparity between these two regions and the construction of factories and manufacturing enterprises in the urban centers, is one of the factors contributing to Iran’s increasing urbanization23.

The present study aimed to compare the risk of cardiovascular events in metropolitan and rural areas in the south of Iran using the ASCVD risk score. ASCVD risk score tool is known as the ‘one-size-fits-all’ approach. Although having some inherent limitations, it remains a simple-to-use strategy in the clinic making it the front line of cardiovascular evaluation based on demographic and conventional risk factors24. Also, since our participants were from a general and apparently healthy population, this scoring system was utilized.

Results

The final studied population (n = 12,359) contained 6,258 FACS participants and 6,101 individuals from SHS (Fig. 1) with a mean age of 51.3 ± 7.8 years and 5,850 men (47.3%). Table 1 demonstrates the differences between the participants from rural and urban areas in socio-demographic, anthropometric, laboratory data, and CVD risk factors. The participants from FACS were younger than SHS participants but there was no statistically significant difference in case of sex distribution between the two groups. The participants who lived in rural areas had higher mean BMI, waist, wrist, and hip circumference than those who lived in Metropolitan areas. The participants from the rural areas were more likely to be married, have lower educational attainment, and lower class occupation, in comparison with the participants from Metropolitan areas. Although the LDL level was not significantly different between the two groups (p-value: 0.221), participants from the rural areas had lower cholesterol, triglyceride, FBG, systolic blood pressure, and higher HDL levels. While the prevalence of hypertension was not significantly different between the two groups (p-value: 0.168), diabetes was more prevalent among participants from metropolitan areas. Also, the prevalence of smoking and opium consumption was higher in metropolitan areas; whereas, the prevalence of alcohol consumption was higher in Metropolitan areas. Finally, the participants from the Metropolitan areas had a significantly higher mean ASCVD risk score, in comparison with those from rural areas (5.51 vs. 4.43, p-value < 0.001).

Fig. 1
figure 1

The study population.

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Table 1 Comparison of characteristics of the studied population in Fasa Adult Cohort Study (FACS) and Shiraz Heart Study (SHS).
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Figure 2 depicts the distribution of rural and metropolitan participants among ASCVD risk score categories. In both groups, the majority of participants were classified as low-risk. The prevalence of participants from Metropolitan areas was higher than rural areas in the low-risk category. The prevalence of borderline, intermediate, and high-risk categories.

Fig. 2
figure 2

The distribution of participants from rural and metropolitan areas among ASCVD risk score categories.

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Table 2 shows the association between residing in metropolitan /rural areas and the ASCVD risk score as a continuous variable using linear regression. The unadjusted model (Model 0) indicated that living in metropolitan areas significantly increased the ASCVD risk (β = 1.07; 95%CI, [0.87, 1.28]; p-value, < 0.001). Given the higher mean age of the metropolitan participants and to minimize the effect of sex difference between the two groups, the association between living in metropolitan /rural areas and CVD risk was adjusted for age and sex (model 1). The adjustment for age and sex, weakened this association, however it remained significant. In model 2, the association between living in metropolitan /rural areas and ASCVD risk score was adjusted for sociodemographic factors such as marital status, occupational class, and educational attainment, which strengthened the association. In the next step, the association was adjusted for the anthropometric covariates including BMI, wrist, and waist circumference which resulted in a weaker, but still significant association (Model 3). Finally, adjusting the association for opium and alcohol consumption showed a modest effect. Sex-stratified analysis showed that these associations were consistent among both men and women.

Table 2 Linear regression model to show the 10-year ASCVD risk score (continuous as percent) in the metropolitan area versus the rural area after adjustment in different models.
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Discussion

Our findings indicated that residing in Metropolitan areas is associated with a higher risk of cardiovascular diseases compared to living in rural areas. Participants in the metropolitan areas had a higher prevalence of the established cardiometabolic risk factors such as diabetes, high systolic blood pressure, obesity, and hypercholesterolemia which are components of the ASCVD risk score. However, people in metropolitan areas had higher job class, educational attainment, and lower rates of smoking and opium use, but higher alcohol use. Also, people in rural areas had better status on obesity indicators such as lower BMI, wrist, and waist circumference. Living in metropolitan areas increases the CVD risk by increasing the conventional CVD risk factors like dyslipidemia, obesity, high blood pressure, and diabetes.

In line with our study, a recent study in Iran by Ebrahimi et al. showed male participants and participants living in urban areas were at a higher risk of developing CVD in the next 10 years25. Also, a systematic review in 2014 indicated urban residents have a higher risk of cardiovascular diseases and prevalence of CVD risk factors; however, they are growing rapidly in rural areas26. A study in Bangladesh found that migration from rural areas to cities increased the risk of CVD. Also, long-time residence in the cities was associated with an increased risk of CVD27. A systematic review of eighteen studies in 2011 indicated that in most studies the prevalence of CVD risk factors such as hypertension, obesity, and dyslipidemia was higher in migrants than in rural groups and lower than people in urban areas. The meta-analysis showed that participants in the urban areas had significantly higher diastolic and systolic blood pressure and BMI than migrants but these differences were not significant between migrants and rural group16. Furthermore, several studies in different countries namely China28, Malawi29, Guatemala30, Ghana31, and Kenya32 supported our findings that the prevalence of CVD risk is higher among participants in urban areas.

In contrast, some studies found that individuals in rural areas had a higher risk of CVD than those in urban areas. A study by S. Yusuf and colleagues based on the data from seventeen countries including Iran, revealed that the CVD risk is lower in urban areas of high-income countries and higher in middle- and low-income countries compared to rural areas33. A study in Malaysia found that CVD risk and CVD risk factors such as smoking, diabetes, obesity, and hypertension are higher in rural areas18. Also, a study in Sweden showed that participants in rural areas had a higher prevalence of CVD risk factors34.

Our study revealed that in addition to established CVD risk factors that are components of the prevailing risk scores, sociodemographic risk factors significantly affected CVD risk. Socioeconomic status including occupational status, income, and educational attainment influences the CVD risk. A study of 1.1 million individuals in Japan showed that higher occupational rank was associated with a higher cardiovascular risk35. In contrast, a prospective study in Sweden indicated the highly-skilled occupational groups had lower CVD risk36. On the other hand, education had a converse association with CVD risk, and people in urban areas had higher educational levels. Previous studies supported our findings that higher educational hierarchy had a protective role for cardiovascular diseases. A study of 38 cohorts indicated that higher educational attainment was associated with a lower risk of cardiovascular diseases37. CVD risk was found to be nearly half in those with higher education levels revealed in a cohort study on 9,226 participants. Also, the authors claimed that certain risk factors including BMI, diabetes, and hypertension were significantly associated with the CVD risk38. Also, a prospective study of more than 154,000 individuals from rural and urban areas of 20 countries found that lower educational level was a CVD risk factor in low- and middle-income countries39. Furthermore, a systematic review in 2017 revealed that health education improved CVD risk and its risk factors by increasing physical activity40. Therefore, increasing the knowledge of people in rural areas could pave the way for CVD primary prevention.

In this study, smoking and opium use were more prevalent among individuals from rural areas, while alcohol consumption was more common in urban areas. Also, our results showed that alcohol and opium use had a modest effect on the association between living in urban/rural areas and CVD risk. Previous studies have shown opium intensified the CVD risk41,42. However, the current evidence indicates that the effect of alcohol consumption on cardiovascular health is dose-dependent. Inconsistent findings were reported regarding the relationship between alcohol consumption and CVD. While some studies found no significant association43,44, others reported that alcohol consumption leads to important malfunctions in the cardiovascular apparatus such as atrial fibrillation45,46. Also, WHO repeatedly disseminates this notion that there is no safe and healthy amount for alcohol intake47. Therefore, policies should be taken into action to encourage quitting tobacco use and opium in rural areas and alcohol use in urban areas.

Another reason for well-controlled diabetes and hypertension is the healthcare policies in rural areas of Iran. In rural areas, some of the community members were trained to provide primary health care in their own local communities as health care workers (Behvarz). Behvarz workers are trained to identify new cases of some specific diseases namely diabetes and hypertension. Behvarz workers follow the identified cases to improve their management by teaching healthy lifestyle, referring to the physician as needed, and checking their adherence to the treatment through regular visits which is an active process. Patients will be contacted if they miss a visit session and Behvarz workers reach their houses if they miss several appointments or do not answer their phones. Unfortunately, this system is not applied routinely in urban areas of Iran48,49. On the other hand, people in urban areas have better access to advanced healthcare facilities.

A national study reported that rural mortality rates exhibit dynamic spatial patterns that vary over time50. Another study at the national scale declared that both urban and rural areas experienced an annual decrease in avoidable mortality rates of 3.33%; however, Ischemic Heart Disease (IHD) and the transition from preventable to treatable death categories had an impact on these decline rates. Rural areas had greater declines than urban areas in the category of preventable deaths, but the annual decline rate for the IHD category was almost the same in both. Nonetheless, there was no statistically significant decrease in treatable mortality in either urban or rural areas51.

In one national study, the 10-year risk of incident coronary artery disease (CAD) as well as the 10-year risk of fatal atherosclerotic events were measured in a population of 25–64 years old participants. It was revealed that the mean Framingham risk score is remarkably high, and about 20% of the Iranian population was assumed high-risk for the incidence of CAD. Being male and older age augmented this risk. Intriguingly, urban and rural residents showed no significant difference neither in risk score nor in frequency of high-risk participants52. A high risk of cardiovascular events in the Iranian population was previously reported by other investigators53,54. A recent retrospective study among more than 2.1 million participants in the United States revealed that CVD mortality rates are significantly higher in rural areas due to poor healthcare facilities55. One foreign study compared the risk factors and characteristics of carotid atherosclerosis in populations at high risk of stroke in rural and urban settings. In the urban population, high-density lipoprotein cholesterol was protective, while higher education, high salt intake, passive smoking, family history of stroke, and transient ischemic attack were distinct independent risk factors. According to the study, urban and rural populations have different risk factors for carotid atherosclerosis56.

In an intriguing survey, disparities in cardiovascular risk profiles among three groups of rural, urban, and rural-to-urban migrants were examined. The migrant group’s risk levels were in the middle of those of rural and urban populations for the majority of risk factors. Compared to both the rural and migrant groups, the urban population had a higher prevalence of hypertension. The migrant and rural groups were comparable in terms of HbA1c, despite the urban group having higher levels. Triglycerides in the three groups did not differ from one another. The age at which migration takes place also affects the cardiovascular risk profile among migrants. This finding suggests that urbanization does have a negative impact on cardiovascular health57.

Strengths and limitations

Our study had some strengths. This study was conducted based on the validated data from the FACS and SHS with detailed and comprehensive variables that allowed us to acknowledge the CVD risk factors in both populations. Also, our study addressed the modifiable risk factors in the rural and urban areas in the south of Iran, providing valuable insight into CVD primary prevention strategies.

Several limitations should be acknowledged in this study. First of all, the ASCVD risk score was used instead of the actual 10-year incidence of CVD in this study. Therefore, further research with a longitudinal study design is needed in the future. Second, there are still some CVD risk factors like physical activity and dietary patterns that we could not compare between these two populations. Third, this study may have differential measurement bias, because the data from two distinct cohort studies were included which was collected by different teams. However, most of the questionnaires were similar and the data for this article was objective.

Conclusion

In conclusion, living in urban areas was associated with a higher CVD risk. Notably, socioeconomic parameters including marital, occupational, and educational statuses seem to have a strong impact on cardiovascular risk factors. Residing in the cities increased the established CVD risk factors such as diabetes, dyslipidemia, hypertension, and obesity. Smoking, opium use, and lower educational attainment were the CVD risk factors of living in rural areas. Therefore, using lipid-lowering and anti-hypertensive drugs alongside lifestyle modification are recommended in metropolitan areas. Smoking cessation and health educational interventions are suggested to demote the CVD risk in rural areas.

Method and materials

Study Design and Population

The present cross-sectional study integrated and compared data from two cohorts: The Fasa Adult Cohort Study (FACS) and the Shiraz Heart Study (SHS). The study included participants aged 40 to 70 years old and without prior history of CVD.

The FACS protocol and profile were explained in detail in previous studies58,59. This research focused on 10,138 adult participants (aged 35 to 70 years) from a rural area in Fasa County, located in Sheshdeh, the eastern part of Fars province, Iran. The majority of the residents were involved in agriculture or animal husbandry, leading to high levels of physical activity, compared to the urban population. Furthermore, their diet primarily consisted of homemade and fresh foods.

The protocol for SHS was previously reported60. Briefly, this study is the first to investigate cardiovascular diseases and their risk factors in a metropolitan area in Iran. The study recruited 7,225 participants with a cluster sampling method from the family physician system in Shiraz metropolis60. Shiraz, the capital of Fars province, is a prominent metropolitan area in Iran, boasting a population of approximately two million residents and covering an area of 240 square kilometers. This bustling urban area is home to a sophisticated public transportation network, comprising buses, two metro lines, and a fleet of 12,000 taxis. The Shiraz metro system consists of two lines spanning over 28 km in total, facilitating an impressive annual ridership of 18 million passengers. The majority of residents in Shiraz are engaged in complex urban activities, mainly working as employees or in non-agricultural occupations, reflecting Shiraz’s urban-centric lifestyle61.

Measurements

The demographic features were collected based on the reports of individuals and their documents, including sex (male/ female), age (year), education (None, no education/ Low class, primary and secondary school/ Medium class, college/ High, university), job (None, no occupation/ Low class, no skill and no education/ Medium, skilled and no education/ High class, skilled and educated), and marital status (married / unmarried (single, widow, divorced)). The habits, including smoking, opium addiction, and drinking alcohol were asked and completed based on ICD-10 guideline62,63.

The medical history and chronic non-communicable diseases of participants such as diabetes, cardiovascular diseases, history of myocardial infarction, and hypertension, were reported based on the visit of a physician. Also, the anthropometric features, including height (cm), weight (kg), body mass index (BMI, kg/m2), waist circumference (cm), wrist circumference (cm), hip circumference (cm), and blood pressure (mmHg) were assessed. The serum level of fasting blood glucose (FBG), triglyceride (TG), cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL), were measured by biochemical tests and reported in mg/dl.

ASCVD risk score

We utilized the atherosclerotic cardiovascular disease (ASCVD) risk score to estimate the 10-year CVD risk. The ASCVD risk score was first introduced by the American College of Cardiology/American Heart Association (ACC/AHA) in 2013 and remains fundamental in the primary prevention guidelines. The calculation of the ASCVD risk score involves variables such as sex, age, systolic blood pressure, total cholesterol, HDL, history of diabetes, smoking, and antihypertensive drug use for individuals aged 40 to 70 years64. Although the ASCVD risk score was based on the data from the United States cohorts, a recent study showed that the ASCVD risk score had an acceptable performance in the Iranian population65. Our previous study66 provides detailed information on the ASCVD risk score calculation. The risk score is classified as follows: Low-risk: < 5%, Borderline: 5–7.5%, Intermediate-risk: 7.5–20%, and High-risk: ≥ 20%.

Statistical analysis

The categorical and continuous variables were reported as frequency (percent) and mean ± standard deviation. The data were analyzed in IBM Inc. SPSS version 16. The independent sample t-test and chi-square test were applied to compare the variables among two cohorts of FACS and SHS. Adjusted and unadjusted linear regression was applied to evaluate the association of living in urban versus rural areas with ASCVD risk adjusted for some covariates. A significance level of p-value < 0.05 was used to determine statistical significance.