The paper assesses the relationship between CVD mortality and socioeconomic and cultural variables in the adult population (over 30 years of age) across countries from 2013 to 2017. The aim of this paper is not to examine the causal relationship between CVD mortality and socioeconomic and behavioral factors, but to investigate the global situation of CVD mortality and to raise / explore some research questions about these associations. To do so, we perform a statistical analysis using traditional regression models that incorporate spatial dependence and allow us to investigate the relationship between them.
Mortality by cardiovascular diseases are related to population age structure, prevalence of risk factors, health conditions, institutional factors, the environment, and the socioeconomic situation to which the population is exposed [8, 13]. In other words, there are several determinants and drivers, but that, in most cases, are not uniformly distributed across countries. Below we present further evidence of the relationships studied separated by continents.
Our findings indicate that, in Oceania, with the exception of Australia and New Zealand, the other countries have high CVD mortality rates and low GDP per capita. According to Roth et al. , significant declines have been observed in the age-standardized CMRCVD over the past two decades in many middle-income countries, except for several countries in Oceania. Regarding urbanization, Oceania is a peculiarity since most countries are located on islands (island countries). Although some of the smallest nations in this part of the world have the highest rates of urbanization, such as Fiji, Kiribati, and Marshall Islands, most of the countries studied are in the low quintile, with an average urbanization of 22%. The expected years of schooling are mainly in the low and medium quintiles, although in Australia and New Zealand the number of years of schooling that a child of school entrance age can expect to receive is 23.3 (the highest value registered among all the countries studied) and 18.9 (ranked in sixth) years, respectively. On the other hand, most of the countries are located in the highest quintile in relation to the prevalence of daily smoking, being that among the five countries with the highest prevalence, three are in Oceania (Kiribati, Papua New Guinea, and Tonga). These countries had a higher estimated prevalence of daily smoking among women when compared to others in the region, while for men the prevalence was greater than 50% in Kiribati, Papua New Guinea, and Timor-Leste .
In Asia, except for cigarettes, the relationship between CVD mortality and the other explanatory variables is quite heterogeneous, a result of their own socioeconomic, behavioral, cultural, spatial, and demographic diversity that characterize the continent. Regarding the relationship between CVD mortality and GDP per capita, of the six countries ranked with the lowest CVD mortality rates, four are in Asia (1st Japan, 2nd South Korea, 4th Israel, and 6th Singapore), all of which are in the high quintile of GDP per capita. At the other extreme, Uzbekistan and Afghanistan, in that order, have the highest CVD mortality rates among all 187 countries studied. In addition, it is worth mentioning the United Arab Emirates, which has one of the highest GDP per capita in the world and is also in the highest quintile of CVD mortality rates. According to Roth et al. , significant declines in the age-standardized CMRCVD occurred over the past two decades in many middle-income countries, with the exception of multiple countries in Southeast Asia, as well as Pakistan, Afghanistan, Kyrgyzstan, and Mongolia. Regarding the relationship between CVD mortality and urbanization, the highest percentages of urbanization are located in the Persian Gulf region (Iraq, Israel, Kuwait, Oman, Palestine, Qatar, Saudi Arabia, United Arab Emirates, etc.), East (Japan and South Korea), and Southeast (Brunei, Malaysia, and Singapore) Asian. In these countries, CVD mortality rates are in the low and medium quintiles. In general, in the Persian Gulf countries, oil revenues invested in health and welfare facilities may be an explanation for the reduction in CVD mortality rates . In the second group of countries, policies for obtaining optimal and equitable health for the population are among the main concerns on the public health agenda . The number of years that a child of school entrance age can expect to receive is in the low and medium quintiles in 75% of the Asian countries. According to the Asia Development Bank , while much progress has been made in recent years, indicators still point to serious education and human-resource shortfalls across the region. Finally, the prevalence of daily smoking is in the middle and high quintiles in approximately 89% of Asian countries. Ng et al.  point out the prevalence of smoking among women in Nepal was comparatively higher than other Asian countries. On the other hand, estimated prevalence was very high among men in South, Southeast, and East Asia.
In Europe, Eastern countries have higher CVD mortality rates than other countries on the continent, although they have declined rapidly over the past twenty-seven years of available data (1990–2017) . Regarding the relationship CVD mortality-GDP per capita, there is a transition in the east–west direction between low mortality / high GDP per capita to high mortality, especially in countries that belonged to the former Soviet Union (USSR), and medium / high GDP per capita. The percentage of urbanization is mainly in the medium / high quintiles. Whether in relation to the urban land expansion or increasing population share, urbanization in Europe is an ongoing phenomenon . The relationship between CVD mortality rates and schooling is almost similar to that observed between the former and GDP per capita. In 80% of countries, the expected years of schooling is at the highest quintile. This says a lot about the many good indicators found in European countries, since education stimulates economic growth and improves people's lives through many ways, including improving health . The prevalence of daily smoking is also observed at the highest quintile for 77% of countries. Greece, Bulgaria, Russia, Cyprus, and Bosnia and Herzegovina are the European countries with the highest prevalence and also those where health risks are most likely to occur . Moldova deserves special mention, as it is the only country on the continent that has high CVD mortality rates and is in the low quintile of GDP per capita, urbanization, and schooling, and high quintile of cigarette use.
In Africa, it is observed that CVD mortality rates are mainly in the medium / high quintiles. Although Africa is still lagging behind in the stage of epidemiological transition, the prevalence of chronic non-communicable diseases (NCDs), such as cardiovascular diseases, have increased in recent years, while the occurrence of communicable diseases have decreased . On the other hand, 75% of African countries are in the low quintile of GDP per capita, which says a lot about how much the continent still has to go in the fight against poverty and inequality. Regarding urbanization, approximately 64% of countries are in the low quintile, which shows that the continent is still largely rural, although it is one of the fastest urbanizing regions in the world . The relationship between CVD mortality rates and schooling is almost similar to that observed between the former and GDP per capita. The number of years that a child of school entrance age can expect to receive is in the low quintile in 71% of the countries studied. Only three countries (Tunisia, Seychelles, and Mauritius) are at the highest quintile, the last two being islands. At the same time that African countries, in general, present poor indicators for the other explanatory variables, the prevalence of daily smoking is in the lowest quintile for 69% of the countries. However, and according to the WHO , the prevalence of tobacco smoking appears to be increasing in the African region. Overall, there are fewer studies about CVD mortality in Africa. Mensah et al.  investigates cardiovascular mortality trends in Sub-Saharan Africa in the past two decades (1990–2013). They show that CVD mortality represents a small percentage of overall mortality in the region. However, they also suggest that there is a recent increase in CVD mortality related to changes in population age structure and the continuous process of epidemiological transition. In this paper, we find similar trends of CVD mortality in the region and relative high levels of CVD mortality in countries with lower socioeconomic conditions and an increase in smoking (important risk factor). Moreover, the health care system in the region is not mature enough to cover the demands of the population and the region might need to provide a health system for both non-communicable and communicable diseases in the context of changes in population age structure.
In the Americas, CVD mortality is the main cause of death, although there are important regional variations. Recent studies suggest that the number of deaths by CVD will continue to increase in the next few years [68, 69]. Rapid changes in population age structure, high income inequality, urbanization, changes in lifestyle (such as unhealthy diets, increased smoking and obesity and decreased physical activity), and limited access to effective health care are the main causes of the increasing importance of CVDs. According to Roth et al. , from 1990 to 2015, Brazil, Canada, and the United States showed a significant decline in the age-standardized CMRCVD. In the United States, Acosta et al.  show that CVD mortality is higher than in other countries with similar levels of development (Europe). In recent years, mortality levels have been declining much slower, with much of this stagnation explained by an increase in CVD mortality in working-age population and negative impacts of alcohol use and obesity in the trends of CVD mortality in the US. In addition, Peru had the lowest CVD mortality rates among countries on the continent and was ranked 4th overall. Regarding the relationship between CVD mortality and GDP per capita, there appears to be a clearer division between North, Central, and South. The farther from the equator, the lower is the mortality rate and the higher the GDP per capita. As for urbanization, in 2014 Central and South America became the most urbanized regions in the world, where 80% of the population lived in cities . The expected years of schooling in 57% of the countries are in the medium quintile. Urquiola and Calderón  state that if the overall enrollment rates are considered, it shows that Latin America countries spend substantial resources on education. Finally, the prevalence of daily smoking is in the lowest quintile for 63% of the countries. However, there are large variations within the region. Bolivia, Chile, and Uruguay are the only countries that have CVD mortality rates and prevalence of daily smoking in the low and high quintiles, respectively. For women, Chile and Uruguay have much higher estimated prevalence rates than other countries in the region . Regional health-system planning needs an understanding of the absolute burden of cardiovascular disease and the effect of demographic and economic changes. Regions with a declining incidence of cardiovascular diseases may still need to invest heavily in health promotion and treatment given trends in population age structure that might increase the number of deaths from this specific cause. In addition, some countries in Latin America might need to invest heavily in the healthcare system and preventable policies to reduce the possible impacts of CVD mortality [73, 74].
In summary, regional disparities in the distribution of health-disease patterns among countries are very important [13, 75]. In most low- and middle-income countries there is still high prevalence of communicable diseases (diarrhea, lower respiratory, HIV / AIDS, tuberculosis and other common infectious diseases), while in more developed economies and those at an advanced stage of the epidemiologic transition process, the prevalence of chronic non-communicable diseases (NCDs) is observed, in particular, cardiovascular diseases.
We argue that this study provides useful clues for policymakers establishing effective public health planning and measures for the prevention of deaths from cardiovascular disease. The reduction of CVD mortality can positively impact GDP growth because increasing life expectancy enables people to contribute to the economy of the country and its regions for longer. Some important research issues raised by this paper should be considered in future studies. The relationship between CVD and income, and other socioeconomic variables, are important. In addition, it is important to understand how changes in individual behavior across different countries might affect future trends in CVD mortality, especially related to smoking and dietary behaviors. Some studies show a reduction in the decline in CVD mortality in high-income countries . However, in less developed regions of the world, we observe increasing levels of CVD mortality and still relatively low levels of economic development. Thus, future research should focus on the trends of less developed economies in terms of health behavior and mortality trends. How are health measures dealing with the aging process and changes in population behavior? Finally, it is important to consider how public and private health care systems are organized and organizing themselves to deal with these changes across the globe. These questions need to be on the research agenda.
However, this research is also subject to limitations. First, our study is at the aggregated level and there might be important variations within countries and among individuals. As shown before in other studies, some regions of very large countries can behave quite differently on the relation between development and cardiovascular mortality [26, 76, 77]. In the case of CVD mortality, further research should investigate individual behavior and its relation to the macro environment to obtain further knowledge on proper interventions to reduce the levels of mortality. Our study is also limited by the availability of explanatory variables that help to understand levels and trends of CVD mortality across countries. We were limited that variations that are available for all countries and, in some cases, they also present their limitations. Finally, a large percentage of countries do not have a proper operational civil registration and vital statistic (CRVS) system, thus mortality and causes of deaths are based on analytical models using data from regions with adequate data. This reinforces the importance to build and invest in CRVS systems across the globe .