Trend of incidence rate of age related diseases: results from the National Health Insurance Service–National Sample Cohort (NHIS-NSC) database in Korea: A cross- sectional study

Abstract

Background: Age-related diseases (ARDs) do not have a defined category by consensus opinion. This study aims to redefine ARDs in Korea, which is about to have a super-aged society, and to examine the incidence rate of ARDs and identify their characteristics.

Methods: Using a National Health Insurance Service-Sample Cohort (NHIS-NSC), which sampled 1 million individuals who maintained health insurance and medical benefit beneficiaries in Korea for one year in 2006 and followed up from 2002 to 2019, we selected 14 diseases with high disease burden and prevalence among Koreans from 92 ARDs diseases defined in the GBD study as ARDs. The annual incidence rate is the number of subjects newly diagnosed with each ARD each year for a total of 14 years from 2006 to 2019, after excluding subjects with a history of being diagnosed with ARDs from 2002 to 2005. The incidence rate by age was divided into units of 10 years by age as of 2019, the number of subjects with aging-related diseases for each age group was used as the numerator, and the incidence rate of each age group was calculated by age group as the denominator.

Results: From 2006 to 2019, the diseases that showed a decrease in the annual incidence were chronic obstructive pulmonary disease, congestive heart failure, and ischemic heart disease, and diseases that showed significant increase were dyslipidemia, chronic kidney disease, cataract, deafness, and Parkinson's disease. Notably, hypertension, diabetes, cerebrovascular disease, osteoporosis, osteoarthritis, and age-related macular degeneration showed a gradual decrease in the incidence and tendency to increase after 2015. However, almost all diseases showed a difference in degree when the incidence rate of each disease was examined, regardless of the difference in the incidence rate by year; however, the incidence increased exponentially as the age increased, and then at a very high age demonstrate a characteristic form of decrease.

Conclusions: The incidence of diseases belonging to the newly defined ARDs increased exponentially with age and had a common characteristic showing that incidence decreased at a very high age.

Introduction

The elderly population is observed to increase worldwide [1]; additionally, Korea is particularly showing the fastest aging rate among major OECD countries [2]. According to the report of the National Statistical Office, from 1970 to 2018, the rate of aging in Korea is observed to increase at an average annual rate of 3.3%, and Korea is expected to enter a super-aged society in 2025 [3]. An increase in the elderly population is a significant cause of increased medical expenses and the financial burden of health insurance [4]. For example, in 2019, medical expenses for the elderly (age ≥ 65 years) in Korea accounted for 41.6% of the total medical expenses and increased by 9.3% over the past decade. In addition, the annual medical cost per elderly individual is 4.91 million won, three times the annual medical cost per non-elderly individual [5].

It is essential to pay more attention to age-related diseases (ARDs) as a significant portion of medical expenses and health care burden will be concentrated on the elderly population with the rapid advent of the age of super-aging. ARDs generally referred to diseases that increase the incidence with age, including chronic diseases, such as hypertension and diabetes, cardiovascular disease, cerebrovascular disease, Alzheimer's disease, Parkinson's disease, age-related macular degeneration, osteoarthritis, osteoporosis, and cancer [6–12]. However, no consistent consensus has defined the disease categories included in ARD. The distinction between normal aging, which occurs naturally with advancing age and pathological aging is not clear. As geriatric diseases are a combination of an aging-related decline in function and disease, the disease categories included in ARD are slightly different depending on the literature [6–12]. Among those, we focused on the 92 ARDs classified by defining age-related diseases as those with exponentially increasing incidence with age, out of a total of 293 causes of disease from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 [13]. They evaluate the burden of each disease of ARDs using the disability-adjusted life-years (DALYs), and ARDs are accounted for 51.3% of the total disease burden globally based on the data from the 2017 GBD, and the top 10 diseases that had the largest absolute increases in number of DALYs between 1990 and 2019 include six diseases corresponding to ARD, such as ischemic heart disease, chronic kidney disease, lung cancer, and senile hearing loss [14]. Additionally, research results show that ARDs show common characteristics in their incidence despite being of different disease groups and having different pathological characteristics. According to this, the incidence rate of ARD increases with age; however, the incidence rate decreases with a very high age [15].

Therefore, we tried to redefine ARDs in terms of the disease burden to provide information for the management and prevention of the elderly population in Korea and analyzed the characteristics by evaluating the incidence rate of each disease of ARD defined in this manner.

Methods

Results

Discussion

In this study, 14 diseases were selected, and the incidence of each disease was confirmed by defining ARD as a disease with a high prevalence in Koreans when the incidence increases with age. According to this, the diseases that decreased in the annual incidence from 2006 to 2019 were chronic obstructive pulmonary disease, congestive heart failure, and ischemic heart disease. Diseases with an increasing yearly incidence rate were dyslipidemia, chronic kidney disease, cataract, deafness, and Parkinson's disease. In the case of hypertension, diabetes, cerebrovascular disease, osteoporosis, osteoarthritis, and age-related macular degeneration, the incidence rate, which had gradually decreased, showed a tendency to increase after 2015. However, when the incidence rate of each disease was examined by the age of 10 years, almost all diseases, regardless of the difference in the incidence rate by year, had differences in degree; however, the incidence increased exponentially as the age increased, followed by a very high age showed a characteristic form of decreasing. There was a slight difference in the age at which the highest incidence rate of each disease was observed; however, most of the cases appeared to increase and then decrease at approximately 70 ~ 80 years of age.

Each disease included in the ARD group is caused by different causes affecting various organs, such as mutations, dysregulated homeostasis, fibrosis, and degenerative processes [9]. However, previous studies have shown that diseases belonging to ARD tend to increase approximately exponentially with age and then decrease in very old age; additionally, the slope of the rising portion of the incidence curve is similar at 6–8% per year [19, 20]. This similarity suggests that a general biological aging process dominates the pathogenesis of various diseases, which can be explained by the accumulation of senescent cells and differences in individual susceptibility to diseases [15].

Senescent cells stop dividing cells in response to various stresses and accumulate in the body with increasing age. They secrete Senescence Associated Secretion Profile (SASP) to induce inflammation or reproduce normal cells [21]. According to one study on the relationship between age and senescent cells, the turnover of senescent cells produced and eliminated rapidly occurs at a young age; however, with increasing age, the turnover slows, especially the rate of elimination [22], and this was used to develop a statistical probability model for the generation and removal of senescent cells. This is called the Saturated-Removal (SR) model, and it can be confirmed that the accumulation of senescent cells occurs because the generation of senescent cells increases by various stresses as the age increases; however, the self-removal rate slows down [23]. Nevertheless, since the number of senescent cells is different in individuals, the rate of removal of senescent cells has various distributions. If it is assumed that death occurs when senescent cells exceed the threshold, the SR model can explain the distribution of death time [22–23].

Since aging cells are associated with several ARDs, if ARDs occur when ARDs exceeds a specific disease-specific threshold, aging cells secrete SASPs that affect the 'physiological parameters' related to the occurrence of certain diseases, causing the disease to exceed the threshold. Therefore, it can be explained that the number of aging cells increases exponentially with age, and the disease increases exponentially with age [15].

Also, the decrease in the incidence at a very high age can be explained by differences in individual susceptibility to specific diseases [24–25]. Each population has a different susceptibility to disease due to the differences in genetic or environmental factors; therefore, the risk of developing a disease may appear differently. Thus, the onset of ARD will occur in individuals with a low threshold for each disease, and ARD will not occur during normal aging in a population with a high disease threshold. However, at a very high age, most people with a low threshold for the disease will have already been afflicted with the disease, and most of the remaining people have a high threshold for the disease; therefore, the probability of developing a new disease is relatively low, resulting in a decrease in the incidence.

Some limitations of this study are as follows. First, since the collected claim data were used for management purposes for insurance claims and refunds, information, such as diagnostic codes might be inaccurate, possibly affecting the incidence rate, and second, because of this, the actual disease may have been underestimated or overestimated compared to the number of occurrences. Finally, because the disease category of ARD was selected through an expert meeting based on the ARD proposed by Chang et al. and published data, there is a limitation since the DALY on the exponential increase in the incidence rate was calculated and not based on the ARD.

However, this study is significant and has meaning because it is the first to show the characteristics of ARD in the Korean population, which increases exponentially with age, and decreases at a very high age, based on a sample cohort of 1 million representative Koreans.

Conclusion

As in previous studies, our findings showed that the incidence of diseases belonging to defined ARDs increased exponentially with age and had a standard feature that decreased at a very high age. Understanding the general characteristics of ARD and its disease burden could help provide public health policies for healthy aging.

Declarations

Ethics approval and consent to participate

The Institutional Review Board of National Health Insurance Service (NHIMC) Ilsan Hospital approved the current study (approval IRB number: NHIS-2021-1-459). The need for patient consent was waived by the Ethics Committee of the IRB of NHIMC Ilsan Hospital owing to the retrospective nature of the study and the strict anonymization of data. All methods were conducted in accordance with the ethical standards of the 1964 Declaration of Helsinki and its later amendments, or comparable ethical standards.

Consent for publication

Not applicable.

Data Availability Statement

Data cannot be shared publicly because health information data which are collected, managed, and maintained by the National Health Insurance Corporation to be modified as requested in the purpose of policy and academic research, however it can be requested from the corresponding author if there is a reasonable request.  

Competing Interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

This research was supported by the National Health Insurance Service Ilsan Hospital Fund (grant number 2021-20-014) 

Author’s contributions

In sun Ryou: Conceptualization, Methodology, Writing - Original Draft, Writing - Review & Editing. Sang Wha Lee: Conceptualization, Methodology. Hanbit Mun, SungYoun Chui: Methodology, Statistical analysis, Kyunghee Cho: Conceptualization, Formal analysis, Writing - Review & Editing, Supervision, Funding acquisition. 

Acknowledgements

Not applicable.

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