In Spain, throughout the first 2 decades of the twenty-first century, there was a decrease in avoidable mortality and in mortality from all other causes of death, both in rural and urban areas. A greater reduction was observed in avoidable mortality than in mortality from all other causes of death. Large urban areas and rural areas showed the largest and smallest reduction in avoidable mortality and in mortality from all other causes of death. As consequence, the mortality advantage found in rural areas at the beginning of the study period was reduced or disappeared at the end of it. In general, the reduction in mortality from the main avoidable causes of death according to area of residence showed a similar pattern, except in women in mortality from infectious diseases, diabetes, and heart disease.

As in our study, other investigations carried out in different rich countries have also shown a greater reduction in avoidable mortality than in mortality from all other causes of death (Karanikolos et al. 2018; Nolasco et al. 2018; Mackenbach et al. 2017). These findings have been attributed to advances in treatment for certain diseases, which means that health services are more effective in reducing premature deaths in patients suffering from these diseases. The efficacy of health promotion and disease prevention measures may also have contributed to these findings.

Deaths from treatable cancers and cardiovascular diseases account for about 85% and 80% of avoidable deaths in men and women respectively. Advances in treatment for these conditions explain this important reduction in avoidable mortality. To this must be added the contribution of measures to reduce health risk behaviours, in the case of cardiovascular diseases, and the contribution of early disease detection programs, in the case of cancers. In Spain, the percentage of smokers in 2003 was 34% in men and 22% in women, while in 2019 it was 23% and 16% respectively. Likewise, the percentage of sedentary people between 2003 and 2019 was reduced from 41% to 32% in men and from 52% to 40% in women (Ministerio de Sanidad 2022a). On the other hand, in the first 2 decades of the twenty-first century, an increase in the coverage of early cancer detection programs was observed, reaching 80% of the target population in 2019 for breast and cervical cancers and 32% for colon cancer (Ministerio de Sanidad 2022a).

Other causes of death, such as infectious diseases, contribute little to the overall number of deaths from avoidable causes. However, mortality from infectious diseases was the one that showed the greatest reduction throughout the period analysed. Most probably, the effectiveness of the vaccines is behind this finding. Throughout the period analysed, coverage of diphtheria, tetanus, polio, measles, and whooping cough vaccine was greater than 95% (Ministerio de Sanidad 2022b).

In contrast, mortality from pneumonia and influenza showed little reduction, and therefore the decrease in mortality from respiratory diseases was of little magnitude. Variation in the number of deaths from pneumonia and influenza, as a consequence of influenza epidemics over time, may explain this finding. Digestive diseases were another cause of death whose mortality experienced little reduction. Most of the avoidable digestive diseases require surgical treatment — appendicitis, abdominal hernia, and cholelithiasis and cholecystistis — and mortality from these health problems is probably related to suffering from concurrent chronic diseases.

Lower accessibility to health services in rural areas could explain the lower reduction in avoidable mortality in these areas. The authors of some previous studies carried out in Spain suggested this possibility. For example, two investigations, using hospitalization data in 2006 and primary health care data in 2010, showed a lower frequency of avoidable hospitalization and lower frequency of morbidity in the population of rural areas than in the population of urban areas (Borda-Olivas et al. 2013; Foguet-Boreu et al. 2014; Sarria-Santamera et al. 2015). The authors pointed out that this lower frequency of health problems recorded in hospitals and primary care centres could be due to less accessibility to health services in rural areas. However, in another investigation in which a lower frequency of use of emergency services was found in the population of rural areas, with data from 2006 and 2011, the authors concluded that this finding could imply an overuse of these emergency services in urban areas and not an underuse of those services in rural areas (Sarria-Santamera et al. 2015).

According to the second interpretation, the findings on avoidable hospitalization and morbidity in primary care, together with the lower avoidable mortality and the lower mortality from all other causes of death observed in rural areas in those years, suggest a lower burden of disease in rural areas than in urban areas rather than lower accessibility to services in rural areas. In fact, in different health surveys, only 1% of the Spanish population reported inaccessibility to health services due to transportation difficulties or long distances (Instituto Nacional de Estadística 2022b). In any case, the fact that the population in rural areas shows the lowest reduction in the mortality rate, both from avoidable causes and from all other causes of death, does not support a lower geographical accessibility to health services in rural areas. Likewise, the findings in women about mortality rate from infectious diseases, diabetes, and heart disease, whose greatest reduction was observed in rural areas, do not support this explanation either.

It could be argued that the avoidable mortality itself included a large spectrum of diseases; and for many diseases, patients can seek treatment in an urban hospital, so this may not be affected by the rural access. However, the gateway to the public health care system in Spain is the general practitioner. Likewise, the estimates of the national health surveys, by interviews carried out in 2003 and the last one in 2017, reveal an absence of differences in the frequency of medical consultation in rural and urban areas in Spain (Ministerio de Sanidad 2023). Probably, this absence of difference in medical consultation between urban and rural areas reflects public health coverage. During the study period, the percentage of the population with public health coverage was practically universal: 99% in large urban areas and over 99.5% in rural areas (Ministerio de Sanidad 2023).

In these surveys, the response of the people interviewed about accessibility to health services does not reflect participation in population screening programs. Numerous studies carried out in rich countries have found a lower frequency of use of population screening services in rural areas (Horner-Johnson et al. 2015; Leung et al. 2014). These findings could help explain the higher mortality from treatable cancer in rural areas observed in some countries. Likewise, studies carried out in Spain in the first decade of the twenty-first century also found a lower frequency of population screening in rural areas (Puig-Tintoré et al. 2008; Ricardo-Rodrigues et al. 2015). This could explain the lower observed reduction in mortality from treatable cancers in rural areas than in urban areas, given deaths from colon cancer, breast cancer, and cervical cancer account for three-quarters of deaths from treatable cancers (Instituto Nacional de Estadística 2022c). In any case, geographical differences in participation in population screening programs may be only part of the explanation, since rural areas also show the lowest reduction in mortality from all other causes of death.

On the other hand, the similar trends in avoidable mortality and in mortality from all other causes of death suggest the existence of some other factor related to both area of residence and health. One such factor could be health risk behaviours. However, this explanation is implausible, given that the prevalence of smoking and the prevalence of physical inactivity showed the greatest reduction in rural areas throughout the period considered (Moreno-Lostao et al. 2019).

It could also be argued that the results are due to deaths in older people, since most deaths occur between 50 and 74 years of age. However, the findings by age groups showed a similar pattern. In men, the average annual percentage change in avoidable mortality in people under 15 years of age, in those aged 15 to 49 years, and in those aged 50 to 74 years were, respectively, −6.9%, −5.0%, and −3.4% in large urban areas, and −6.6%, −4.2% and −2.4% in rural areas. In women, the average annual percentage change in avoidable mortality in these three age groups was, respectively, −6.3%, −3.3%, and −3.0% in large urban areas and −-5.1% , −2.7%, and −2.7% in rural areas.

A sociodemographic characteristic strongly associated with mortality is educational level. People with university education show the lowest premature mortality from most leading causes of death (Reques et al. 2014). However, this characteristic cannot be responsible for the findings of the present study, since the percentage of the population with university education, throughout the first 2 decades of the twenty-first century, multiplied by 2 in urban areas and by 3 in rural areas (Instituto Nacional de Estadística 2023)

There is evidence that places where the number of inhabitants is reduced show high mortality rate, while those where the population is growing show low mortality rates (Davey Smith et al. 1998; Molarius and Janson 2000; Davey Smith et al. 2001; Regidor et al. 2002). This could be a consequence of the healthy immigrant bias. That is, people who move to areas with population growth could be healthier than people who stay. In the present study, we have classified the areas of residence into urban and rural and we have found that, between 2003 and 2019, the population increased by 10% in urban areas, but decreased by 3% in rural areas. Therefore, we cannot rule out the possibility that this variation in population size may have contributed to the different trend in avoidable mortality and in mortality from all other causes of death.

In many rich countries, mortality in rural areas is higher than in urban areas. However, in the present study, mortality in rural areas is lower than mortality in large urban areas. Similar findings have been observed at various locations in the UK (O’Reilly et al. 2007; Gartner et al. 2008) and in other countries (Fukuda et al. 2004). Probably the greater reduction in lifestyle-related health risk factors and other exposures in urban areas than in rural areas started earlier in some countries than in others.

One of the strengths of this study is the availability of information on deaths and population in rural and urban areas in Spain in the first 2 decades of the twenty-first century. Another strength is the analysis of a negative control of the outcome variable. It has been observed that the trend in avoidable mortality is similar to the trend in mortality from all other causes of death. One of the limitations is the lack of information on the socioeconomic characteristics of the areas and the inhabitants who reside in them. The socioeconomic profile of the areas and individuals may have varied over time. Likewise, the existence of a numerator–denominator classification bias is possible, given that annual deaths have been analysed but the population corresponds to January 1 of each year. In any case, its influence on the results must have been minimal, since it is unlikely that this bias would have changed from one year to another.

In summary, in the populations of rural and urban areas, a similar trend has been observed in avoidable mortality and in mortality from all other causes of death, which suggests a common factor responsible for both trends. Future research should test whether the increase in population in urban areas is responsible for this finding, as consequence of the migration of healthy individuals to those areas. Likewise, health interventions, in order to reduce the burden of disease, should establish priorities by taking into account that the advantages in mortality of rural areas have been disappearing.