Clustering of the causes of death in Northeast Iran: a mixed growth modeling

One of the sustainable development goals is good health and well-being [23]. A decrease in mortality is considered a sign of a healthy community. The study of death and its causes is an essential topic worldwide, and this research can help in seeking a more sustainable future for the population’s health. As a consequence, it can improve social welfare, life satisfaction, and quality of life [23]. Health promotion includes health education, health protection, and disease prevention. Achieving health promotion requires planning, increasing people’s knowledge and skills, creating policies that support health, and more education by government and non-governmental institutions to improve people’s lives by 2030 [23, 24]. Therefore, without the implementation of these policies and more research, there is no hope of improving people’s health. High-quality research and precise results require collecting high-quality data in a timely manner.

To distinguish the underlying trends of the causes of individuals’ death and longitudinal changes in heterogeneous subgroups, we analyzed data from 2015 to 2019 extracted from Iran’s most comprehensive system for registering causes of death, which is a strength of this study. We clustered 112 causes of death into three classes. The pattern of changes in mortality due to diseases was constant (87.50%). Second-class diseases had a slightly upward trend (8.92%), and third-class diseases had a completely upward trend (3.57%).

Borumandnia et al. clustered 63 death causes among Iranian men from 1990 to 2016 into four classes. They found that the defined trend in mortality rates over time was increasing, slowly decreasing, stable slowly increasing, and almost sharp trend in classes 1 to 4, respectively. They also found that the non-linear growth mixture model was not significant [25].

According to the current study’s findings, except for lymph, hematopoietic system and related tissue, vascular diseases of the brain, high blood pressure disease, and ischemic heart diseases, all other locations showed a completely upward trend (slop = 108.07 and P-value < 0.001) over time.

Ischemic heart disease had a slowly decreasing trend from 1990 to 2016 in Borumandnia et al. study, while after that (from 2015 to 2019), it showed a completely upward trend. High blood pressure is a risk factor and a major cause of CVD and mortality [26].

In 2019, high systolic blood pressure was reported as a leading cause of death, accounting for nearly 10.8 million deaths worldwide [27]. Additionally, hypertension affected 1.28 billion individuals in 2019 [28].

Lifestyle modifications have been shown to effectively improve cardiovascular disease risk factors, as demonstrated in numerous studies and reviews. However, it is important to note that advanced age and higher body mass index are associated with an increased risk of hypertension [29].

Our study revealed that several factors, including diabetes mellitus, cardiopulmonary diseases, pulmonary circulation diseases, various forms of heart disease, influenza and pneumonia, chronic lower respiratory tract diseases, other respiratory system diseases, kidney failure, death due to unknown causes, traffic accidents and transportation-related incidents, and other unintentional external causes of accidents, were classified as second-class factors. These factors exhibited a slight upward trend with a slope of 14.18, but the P-value was not significant (P = 0.520).

Patients with type II diabetes and metabolic syndrome are at an increased risk of developing cardiovascular disease and related events, thereby reducing life expectancy. Consumption of a high-salt, hypercaloric-high-carbohydrate diet leads to hypertension and hyperinsulinemia, resulting in obesity that further aggravates cardiovascular disease. Therefore, dietary interventions are essential to prevent these outcomes and should not be ignored [29]. Studies have shown that long-term weight loss, adoption of a low-calorie dietary pattern, reduction in blood pressure, and use of anti-hypertensive drugs can be beneficial for patients with type 2 diabetes [29].

Boroujeni et al. utilized latent growth mixture modeling (LGMM) to identify different longitudinal trends in lung cancer incidence in Europe from 1990 to 2016. They performed LGMM on male and female sub-groups separately and found that the overall pattern of incidence related to female and male lung cancer was rising and falling, respectively [30].

A systematic analysis of the Global Burden of Disease (GBD) from 1990 to 2015 highlighted the importance of neurological disorders, which accounted for 6.3% of global Disability-Adjusted Life-Years (DALYs). Neurological disorders caused 9.399 million deaths in 2015, accounting for 16.8% of global deaths [31].

Ghadirzadeh et al. showed that between 2001 and 2010, an annual average of 34.6 per hundred thousand people were killed in traffic accidents, with more than 80% of the casualties being men, and a descending trend over time [32]. However, recent data suggest that traffic accidents have experienced a slightly upward trend, indicating the need for increased attention.

Kidney disease is one of the most common chronic diseases with a global prevalence above 10% and a slight upward trend in the second class. It is associated with other chronic diseases, such as obesity, diabetes, and hypertension. Modifying lifestyle, controlling blood pressure, and using anti-hypertensive medication is recommended to reduce the risk of renal failure [33].

According to WHO’s reports, Air pollutants are responsible for 4.2 million premature deaths and various diseases, including 29% of lung cancer, 25% of ischemic heart disease, 17% of acute lower respiratory infections, 24% of stroke, and 43% of chronic obstructive pulmonary disease [34]. The recent outbreak of COVID-19, a respiratory infection disease, significantly increased the number of deaths [8].

With regards to the discussions surrounding the significance of serious and chronic diseases that result in mortality, as well as the identified increasing trend, there is a pressing need for more rigorous measures to be taken. The primary recommendation is the modification of lifestyle, which plays a prominent role in preventing and controlling diseases. The World Health Organization (WHO) has projected that lifestyle-related diseases are the cause of 70% to 80% of mortalities in developed countries and 40% to 50% in developing countries [35].

In their systematic review study conducted in Iran, Ghanaei et al. found that a poor lifestyle is a significant factor, accounting for 53% of deaths, in the incidence of chronic diseases such as colon cancer, hypertension, chronic obstructive pulmonary diseases, hepatic cirrhosis, HIV, and CVD. Adopting a healthier lifestyle can overcome many major risk factors, promote health, and reduce mortality [35]. In addition to a poor lifestyle, the structural weaknesses of health policy-makers, inadequate attention to general health education, and insufficient educational content on health promotion are important and critical issues that require basic planning to be implemented.

Gender and age are significant factors that impact the prevalence, burden of disease, and mortality rates globally. Neurological disorders exhibit a 10% difference in death and DALY rates between males and females, with higher rates observed in males. The majority of the burden due to neurological disorders is borne by individuals in the age group of 0–5 years. Epilepsy is a disease that affects children and young adults and causes the most burden. Headaches peak between the ages of 25 to 49 years, while the burden of other neurological disorders increases with age. Stroke is the primary contributor to DALY. Geographical regions and their variations are also crucial as communicable neurological disorders are more prevalent in high-income regions and central Europe [31].

Other factors such as seasons and residential areas can also affect disease prevalence and mortality rates. Consequently, these factors may impact the clustering of death causes and their longitudinal trends over time. To obtain more accurate results and implement necessary policies in the field of public health to reduce mortality, larger scale studies are recommended, considering a larger sample size, other medical centers, regions, and provinces. Additionally, data analysis with bivariate or multivariate growth mixture models is recommended.

Limitations

Several limitations must be considered in this study. Firstly, the small number of disease causes limited the use of mixed growth models. Secondly, the heterogeneity of diseases resulted in some classes having a small volume. Accurate and high-quality mortality data are crucial for informing public health policy. In some cases, the cause of death may remain unspecified or the cause of death may be recorded for another reason, limiting the discussion about the cause of death.