The results of this comparative study revealed that avoidable causes of death had substantial contributions to Iran’s lower LE and higher LI compared to the three neighbour countries in the region during 2015–2016. We also observed variations in cause-specific contributions by age and sex. For instance, while preventable causes of death had generally higher contributions than other avoidable causes of death among males, their contributions were comparable with other causes in females. In addition, Iran generally performed better on treatable causes of death among people aged 60+ years. Higher maternal/infant mortality and injuries-related deaths resulted in higher uncertainty in timing of death among Iranians than their counterparts in the three neighbour countries.
Substantial contributions of avoidable causes of death to the cross-country gap in LE observed in this study is in line with few previous studies conducted in other parts of the world [15, 24]. Higher mortality rates from avoidable causes in Iran compared with the three neighbour countries studied here is consistent with the findings from the GBD study on Healthcare Access and Quality Index, an index based on 32 treatable causes of death, where Iran had the lowest score (71.8 out of 100) compared with Qatar (81.7), Kuwait (80.7) and Turkey (74.4) in 2016 . While a previous study conducted in the UK reported that preventable causes had the greatest contributions to the cross-country gap in LE compared with other avoidable causes in both sexes , this was only the case among males in the current study. This might partially be attributable to cultural differences between the UK and the Middle Eastern countries in females’ roles in the society. For example, drug- and alcohol-related deaths contributed to 11.2 to 14.7% of the LE gap in females across the countries in the UK , while their contributions were 0.7 to 1.8% in this study. Moreover, the contributions of maternal/infant mortality were negligible in the UK , whereas they were among leading causes of LE gap among females in this study.
Within avoidable causes, injuries were the leading cause of LE disadvantage in all pairwise comparisons among Iranian males, and compared to Turkey among Iranian females. Indeed, injuries alongside diabetes mellitus, hypertensive diseases, other treatable and preventable causes, drug-related death and maternal/infant mortality were the only causes that contributed to LE disadvantage in Iran in both sexes in all pairwise comparisons. Importantly, since injuries-related deaths are more common among younger age groups, they were a leading cause of LI disadvantage among Iranian males and females. These findings are not surprising given the fact that the age-standardized mortality rate caused by road traffic injury in Iran is one of the highest worldwide (22 deaths per 100,000 population in 2019), surpassing Kuwait, Turkey, and Qatar (15, 7, and 7 deaths per 100,000 population, respectively) [26, 27]. In particular, males are disproportionately affected, with road traffic injuries being the second leading cause of disability-adjusted life years (DALYs) among Iranian males compared with 6th, 8th and 10th leading cause of DALYs in Qatar, Kuwait and Turkey, respectively, in 2015 . The higher burden of road traffic injuries in Iran compared with the neighbouring countries might be due to poor road safety, poor quality and safety of cars, inadequate public transportation, risky driving behaviours and low adherence to driving regulations (e.g. the use of seatbelt and helmet), as well as inadequate access to high quality trauma care system . Given the substantial contributions of injuries to LE and LI disadvantages in Iran, urgent intersectoral interventions (beyond the healthcare system) such as re-organisation of traffic laws, transportation infrastructure, and controlling the manufacturing industry are strongly needed [30,31,32]. The WHO non-communicable diseases national plan, together with Iran’s Road Safety Strategy Plan, has set a target of 20% relative reduction in deaths due to traffic injuries by 2025 in the country  and several interventions including more stringent regulations (e.g. compulsory seat belt and speed limit laws), increased fines for traffic violations, random drug and alcohol testing, and improvements in the roads network construction have been implemented . Although these actions resulted in a decline in road traffic injuries in recent years in Iran , these injuries still incur a high burden and Iran is unlikely to achieve the targeted reduction in the national plan. In comparison, Qatar has introduced a trauma system that provides emergency care to every citizen and non-citizen, including education, diagnosis, treatment, rehabilitation, and community reintegration of the injured which resulted in substantial reductions in deaths attributable to road traffic and injuries . Qatar has also invested significantly in upgrading the roads and railways-related services together with reducing the pedestrian accidents through the Decade of Action for Global Road Safety . Turkey is another good example given the solid enforcement of the laws against blood alcohol concentration and driving national standards including enforced regulations on passengers’ protection . Turkey launched a six-pillar program called the “New Approaches, Targets and Solutions on Road Traffic Safety” through an intersectoral strategy involving population education, enforcement, support to traffic services, information, motivation of personnel, and legislative matters . It resulted in a 20% decrease in road injuries in 2010 after 3 years of its implementation [37, 38]. All these measures promoted by Qatar and Turkey can be used as a benchmark for Iran.
Besides injuries, maternal/infant mortality was another leading cause of LE and LI disadvantages in Iran. There were 14.7 deaths per 1000 living births (95% confidence interval [CI]: 10.8–19.5) in Iran in 2015 , right below the average of the EMR (44.2, 95%CI: 41.6–46.9), but almost doubling the rate of the six countries having achieved Millennium Development Goal 4 by 2015 in the region (e.g., 8.2[95%CI: 6.5–10.2] and 8.6 [95%CI: 6.0–12.1] in Kuwait and Qatar, respectively) . Higher rates of maternal/infant mortality offset lower mortality rates for other treatable causes, especially infectious diseases and diseases of the respiratory system in Iran, resulting in an overall negative contribution from treatable causes into LE in Iran in three pairwise comparisons. This higher maternal/infant mortality rates might be due to lower access to high quality maternity care, delayed emergency care provision, high rates of caesarean section deliveries, and lower socioeconomic status especially financial hardship experienced in the recent decade following sanctions on Iran [41,42,43,44]. Specifically, for caesarean delivery, Iran has the second highest caesarean rate in the EMR (48%, right below Egypt with 52%), while Kuwait and Qatar have 12 and 20%, respectively. The ease of access to facility-based delivery, women’s fear of labour pain, and clinicians’ convenience, financial gain and fear of litigation have been explained as the main drivers [45, 46]. Although Iran has experienced steep reductions in maternal/infant mortality in recent decades, it still suffers from higher mortality rates than the neighbouring countries. This highlights the need for further actions including promoting maternal education and improving access to antenatal and postnatal care [42,43,44]. In particular, there is a recent shift in family planning policies toward rising restrictions on access to abortion, contraception and birth limiting surgeries in Iran , which might lead to increased maternal/infant mortality and in turn widening the gap in LE and LI with other countries in the region.
Our results suggested that while IHD was generally associated with LE advantage for Iranian males, it contributed to LE disadvantage for Iranian females compared with their counterparts in the neighbouring countries. Iran is among the countries with the highest rates for cardiovascular diseases (CVD) exhibiting more than 9000 age-standardised cases of CVD per 100,000 persons . IHD has also the highest disease burden, accounting for 26% of total deaths in the country, and with higher incidence rates in females than in males among people aged 70+ years . In addition, a recent study from Isfahan province in Iran reported a greater rise in IHD incidence among females than males during recent two decades . Although it should be noted that despite LE disadvantage from IHD for Iranian females in our cross-country comparison, IHD mortality rates are higher for males than females in Iran. Our results possibly reflect greater cross-country differences in IHD’s risk factors (e.g. hypertension, metabolic syndrome, obesity, socioeconomic and cultural distress, unhealthy lifestyle, low affordability, poor accessibility to primary healthcare)  for females compared with males. For instance, while the age-standardised prevalence of hypertension (19.6%) and dyslipidaemia (58.1%) is higher among Iranian females compared to females in Kuwait (15 and 55.7%) and Qatar (13.6 and 57.6%), the prevalence is generally lower in Iranian males (21.2 and 41.8%) than males in Kuwait (23.1 and 56.2%) and Qatar (19.6 and 56.8%) . Moreover, we speculate that population-based interventions and intersectoral public health policies implemented in Iran in the recent decades might have benefited Iranian males more substantially than Iranian females either due to higher rates of IHD mortality among males or due to unequal access to these interventions. Further analyses are needed to explore the underlying causes of higher IHD mortality rates among Iranian females compared with females in the neighbouring countries.
Avoidable causes could also be prevented if healthcare systems are strengthened. Iran has improved towards universal health coverage (UHC) through the coordination of the Ministry of Health and Medical Education, but free health insurance coverage is not yet a reality for secondary and tertiary health services . In contrast, Qatar, Kuwait and Turkey have national health insurance schemes with a state-fund healthcare system providing free access and treatment to the primary services, avoiding excessive out-of-pocket expenditures (OOP) [53,54,55,56]. The significant share of OOP (35%) from total healthcare expenditure , derived from the dual organisation of the healthcare system (public and private) with the private part providing vast healthcare services, also contributed to socioeconomic inequalities in healthcare use and mortality rates in Iran.
Our study is subject to some limitations. First, the OECD classification utilises an age threshold of around 75 years to calculate avoidable (premature) deaths, which might not mirror specific countries’ characteristics. Deaths in people above 75 years old are not considered avoidable, even though these could have been avoided through the correct prevention or treatment. Future analyses should incorporate specific age-targeted definitions of avoidable causes of death. Second, the causes of death are treated as mutually exclusive although they may be linked to each other. Third, death registration and certifications systems might confront different completeness rates and coding practices, which could bias mortality outcomes and our study findings. For instance, WHO reports that completion rates for death counts provided by countries’ CVRS were 90, 50, 50, 91% for Iran, Kuwait, Qatar and Turkey, respectively ; similar to those reported by the GBD . These discrepancies in countries’ CVRS quality and completeness might be partially responsible for the estimated contributions of avoidable causes of death to cross-country differences in LE/LI in our study. While it is hard to quantify the magnitude of the bias, these problems call for great caution in interpreting our findings. Also, we acknowledge that our analyses were sensitive to the data source used, exhibiting variations in the age structure of all-cause mortality and consecutively on age-specific contribution to LE/LI. The estimates from IHME and UN are modelled estimates relying on assumptions that might not accurately capture the distributions of deaths by age, sex, and cause [59, 60]. For example, the IHME’s estimates rely on the availability of high quality mortality data and when such data for a location, time, age group or cause is not available, the model borrows the data from other sources which include mainly data from high-income countries [59, 61]. However, such data might not accurately represent the distribution of deaths in other locations particularly low- and middle-income countries. In addition, to our knowledge, no comparable data on causes of death by ICD-10 codes are publicly available in other sources, including the IHME and UN. However, raw data from CRVS used in WHO mortality database are prone to coding errors, misclassification bias, imprecise causes of death (“ill-defined” death), and incomplete coverage which can bias the age- and cause-specific contributions to LE/LI . Therefore, complementing WHO mortality data with age-specific deaths estimated from other sources such as IHME, as has been done in the present study, would provide better insights on age- and cause-specific contributions to cross-country gaps in LE/LD. Fourth, avoidable mortality may be indirectly related to the contribution of intersectoral public health policies in each country from a non-causal perspective, but not directly. Finally, even though the countries selected are neighbours, they may differ in their characteristics (e.g., culture and demographic composition), which represent further challenges to quantify the differences between them realistically.