With the increase in life expectancy all over the world, multimorbidity has become a more noticeable public health problem, causing its prevalence was positively correlated with age and it’s associated with poorer life quality, premature death, and an increased need for health care[9–11]. Our study, among more than 200,000 hospitalized elderly patients, revealed that circulatory system diseases, especially hypertension and ischemic heart disease, were the most common conditions in multimorbidities. And many studies have suggested that hypertension and heart disease are the most common chronic diseases[12–14]. These diseases were often accompanied by endocrine, nutritional, and metabolic disorders, particularly diabetes. Besides, compared with 2015–2019, the prevalence of neoplasms in multimorbidity has increased significantly in 2020–2021, which prompts that we need to pay more attention to the public health and clinical research significance of neoplasms in multimorbidity. COVID-19 had a great impact on many social aspects, especially the attention of different diseases[15, 16]. It would also have a great impact on the comorbidity spectrum of hospital inpatients. On the one hand, it might indeed be a change in the disease incidence. On the other hand, some patients with chronic diseases choose not to seek medical treatment due to the fear of spreading COVID-19 or other reasons.
The results of chronic disease comorbidity pattern of the elderly show that among the top ten chronic disease comorbidity combinations, "hypertension + diabetes" is the chronic disease comorbidity pattern with the highest prevalence rate, followed by hypertension and heart diseases (Other forms of heart disease or lschaemic heart diseases). In addition, different types of heart diseases also occur at the same time. From the perspective of network influence, hypertension, diabetes, ischemic heart disease and Other forms of heart disease are the four most common core chronic diseases, and they have the most close interaction and connection with other chronic diseases.
Cardiometabolic diseases as one of the most frequent multimorbidity groups pose a great threat to the life and health of the aged, which is consistent with previous studies[17–19]. Cardiovascular aging and metabolic decline with age are both continuous and irreversible processes that may be facilitated by genetics and poor lifestyle habits[20]. Hypertensive disease is a prominent health issue, not only as a risk factor for cardiovascular morbidity and mortality[21] but also increases the incidence of trauma in aging people[22]. Over the course of this century, the prevalence of hypertension and average blood pressure has declined in high-income regions but increased in less-developed regions. In 2015, 88% of the 8.5 million hypertension-related deaths worldwide occurred in less-developed regions. The onset of hypertension in our country is thought to be related to patients eating too much salt, and we believe that our country still has a lot of work to do in terms of a healthy diet and active health[23].
Diabetes mellitus is a chronic metabolic disease characterized by elevated fasting blood glucose, which can affect both small and large blood vessels and the most prevalent complications are kidney disease, blindness, and amputations[24]. The high economic burden of diabetes also makes the disease an important clinical and public health problem, as shown in the diabetes-related Cost of Disease (COI) study[25]. Fortunately, due to the continuous improvement of China's medical insurance policy and the implementation of the national organization of centralized drug procurement measures, the hospitalization expenditure of elderly multimorbidity patients has decreased in 2020–2022 compared with 2015–2019, which indicates that these measures are of great significance to effectively reduce the economic burden of patients.
As mentioned above, the incidence of neoplasms in multimorbidity has increased significantly in recent years. It might be related to global aging. In 2012, 6.7 million new cancer cases (about half of all cancers) were diagnosed among the aged worldwide, and nearly 48% of these cases occurred in low- and middle-income countries[26]. Meanwhile, it was also affected by COVID-19, which might cause certain difficulties in the treatment of some diseases[27]. In addition, epidemiological studies have found that diabetes is associated with increased incidence and mortality of a variety of tumors, including colorectal cancer and breast cancer[28], this is related to various molecular mechanisms such as hyperglycemia activates cancer-related signaling pathways[29]. It suggested that primary health care institutions could effectively reduce the incidence of chronic disease comorbidity in the elderly or delay its progression by preventing and treating hypertension and improving the efficiency of hypertension management, ultimately improving the physical function and quality of life of the elderly.
With the accelerating process of aging society, comorbidity has become one of the most important health problems faced by the elderly population and gradually attracted widespread attention from the academic community. There are complex associations among comorbidities, which combined with the differences of individual characteristics, further lead to the complexity and heterogeneity of multimorbidities of health management. This study attempts to present the comorbidity relationship and its disease burden from a holistic and systematic perspective through association analysis, to provide a basis for the study of senile comorbidity. Given the complexity and heterogeneity of senile multimorbidities, we have some suggestions. Firstly, we should strengthen multidisciplinary cooperation, such as epidemiology, internal medicine, surgery, oncology, etc., establish multidisciplinary multimorbidities research teams, and utilize their respective advantages to carry out comprehensive research. Secondly, we can establish a large sample, multi-center comorbidity database, collect and collate comorbidity research data and clinical practice experience, and provide more accurate and detailed information for comorbidity research. Thirdly, we can promote and apply advanced technology, such as smart wearable medical devices, gene sequencing, bioinformatics, and so on, in combination with traditional research methods, to carry out in-depth and efficient comorbid research. Moreover, the accuracy, repeatability, and interpretability of comorbidity studies can be improved using multi-layered improved research design methods, while minimizing potential bias. Researchers can apply a variety of research methods, such as cohort study, case-control study, longitudinal study, etc., to analyze the mechanism and influencing factors of comorbidity from different perspectives, and carry out comprehensive and in-depth research on comorbidity.
However, there are some limitations in this study. This is a retrospective study and there may be some unknown biases. Therefore, further research is needed using a prospective study design for older adults. In addition, our study is limited to a single hospital and may not be able to effectively evaluate the impact of demographic and spatial factors, which may be problematic to generalize to regions with different development levels in China. In the following study, a multi-center study should be performed to further analyze and explain the demographic and spatial distribution of multimorbidity.