This study is the first to use intrinsic capacity as a health standard to measure the average life expectancy and healthy life expectancy of elderly individuals in China. Taking the 60-year-old group as an example, the healthy life expectancy of the elderly in China measured in this study was 11.21 more years, which was higher than the healthy life expectancy based on disease. Liu Ying et al. [21] used the 2011 CHARLS data to measure the disease-free healthy life expectancy of elderly individuals in China, and the results showed that the disease-free healthy life expectancy of the 60-year-old group was only 3.2 more years. Disease-free healthy life expectancy is expressed as life expectancy in a healthy state without certain disease, and as the elderly age, the proportion who suffer from chronic diseases increases; the 2022 14th Five-Year Plan for Healthy Aging shows that more than 78% of the elderly population in China have at least one chronic disease [22]. At present, most chronic diseases can be prevented and controlled by lifestyle changes. Kong L et al. [23] found that lifestyle care management can effectively improve medical compliance behavior, reduce the occurrence of chronic disease complications, and thus improve the quality of life of patients. Therefore, using disease as a determinant of health will increase the number of unhealthy people, resulting in a longer unhealthy life expectancy, and a shorter healthy life expectancy. Thus, discussing health in terms of disease no longer meets the health needs of the elderly.
In 2001, the WHO published the International Classification of Functioning, Disability and Health, and scholars from various countries began to use disability or function as a health indicator to measure the healthy life expectancy of elderly individuals. Wang et al. [24] estimated the healthy life expectancy of elderly individuals aged 60 and older in Jiangxi Province, China, in 2018, and the results showed that the disability-free healthy life expectancy of elderly individuals aged 60 was 18.12 more years, which was significantly higher than the results of this study. Disability-free healthy life expectancy evaluates the health status of a population by combining the disability status of a population with life expectancy. In 2006, China conducted a large-scale national sample survey of persons with disabilities, which not only classified disabilities into visual, hearing, speech, physical, intellectual, mental, and multiple disabilities but also graded each type of disability according to the degree of impairment or abnormality [25–26]. Because the determination of disability and disability level is an objective survey based on medical testing standards and even the use of professional equipment by doctors [26], China's disability statistics are relatively low; according to the survey, the total disability prevalence rate of the population ages 60 and older is 24% [27]. Although elderly individuals have defective body parts, if these defects do not affect physical functioning, it is not comprehensive to judge their health based on whether they have physical disabilities.
At present, the most commonly used health indicator in China is the ability to perform the activities of daily living (ADLs). This indicator was originally proposed by Katz, who paid more attention to the physical ability of elderly individuals, and then Lowton et al. extended the concept of ADLs by introducing the ability to perform instrumental activities of daily living (IADLs); both of these indicators are now used to evaluate the ability of elderly individuals to live independently. Wen Yong et al. [28], based on the 2013–2018 CHARLS data, used ADL and IADL as health standards to measure the healthy life expectancy of elderly individuals, and the results indicated that under the ADL standard, the healthy life expectancy of the 60-year-old group in China was 19.8 years. Under the IADL standard, the healthy life expectancy of the 60-year-old group in China was 13.2 years. The data show that the healthy life expectancy measured by ADLs and IADLs is higher than the results of this study, and there are several reasons for the different research results. First, because ADLs mainly measure the physical function of elderly individuals, compared with the assessment of intrinsic capacity, the standard of judging health is relatively low. Thus, the number of healthy people with ADLs as the standard is significantly greater than the number of healthy people based on intrinsic capacity. Older adults with IADL restrictions can achieve the ability to live independently through a variety of social supports that provide the care they need and meet their needs for quality of life. Second, ADL or IADL limitation is usually observed only when a significant decline in function is apparent, whereas the decline in intrinsic capacity, a sensitive dynamic indicator of healthy aging, tends to occur before or even earlier than the onset of age-related diseases or symptoms. Elderly people with reduced intrinsic capacity can be identified through screening and assessment early in life, so the healthy life expectancy based on intrinsic capacity is lower than the healthy life expectancy based on ADLs and IADLs.
Although the reliability and validity of objective measurement indicators such as disease, disability, ADL, IADL, etc., are high, it is difficult to measure large-scale populations, so people expect to find a subjective measurement and a method that can be close to objective health measurement, and some studies believe that health self-assessment is a comprehensive evaluation index that can evaluate all health states [29]. Based on the CHARLS data from 2011 to 2015, Huang et al. [13] calculated the healthy life expectancy of elderly individuals in China with self-rated health as the standard, and the results showed that the healthy life expectancy of the 60-year-old group of elderly individuals in China was 16.2 years. This is higher than the findings of this study, possibly because people self-evaluate their health status by considering lifestyle, disease burden, mental state, social, physical, and emotional factors, and specific cultural factors [29]. Because Chinese people are deeply influenced by the golden mean, they tend to be more neutral in self-rated health options and are more subtle in expressing their opinions than people in Western countries. Second, self-assessment of health largely depends on the subjective empirical perception of the disease in elderly individuals, and many elderly people may subjectively rate their health higher than physical activity status [30].
For a long time, China has employed a disease-centered nursing model for elderly individuals, and with the increase in life expectancy, disease-centered medical treatment has been unable to manage the aging trends. With the development of the social economy, people's demand for health is increasing, the understanding of health is more in depth, and the selection of healthy life expectancy indicators not only includes disability, ADLs, IADLs and other objective measurement indicators but also self-assessment of health. These indicators reflect the development level of healthy life expectancy among the general population in China. However, with the acceleration of the aging process, the health of the elderly has received increasing attention, and the Global Report on Aging and Health released by the WHO in 2015 [5] promoted healthy aging as a strategic measure to cope with population aging worldwide. Intrinsic capacity is the core of healthy aging, enriching the connotation of the health of elderly individuals. As a multidimensional and relatively strict evaluation index, intrinsic capacity fully reflects the reserve function of the elderly population and is committed to improving the quality of life of the elderly and extending their healthy life expectancy.
The results of this study found that the healthy life expectancy of male, urban, and high-income elderly individuals is significantly longer than that of female, rural, and economically disadvantaged elderly individuals, which is consistent with most of the findings. Song L J et al. [31], based on the analysis of healthy life expectancy and its ratio to life expectancy, concluded that the value of elderly men is always higher than that of women, and females and elderly people are at a significant disadvantage regarding their health. Although women have a longer life expectancy with age and social divisions of labor, most women still have to take on heavy household chores and household care after retirement, and their health is less robust than that of elderly men. Huang et al. [13] measured the healthy life expectancy of the elderly population in China by self-assessment of health as an indicator and found that the health status of elderly urban residents was significantly better than that of elderly rural residents; not only was the average life expectancy longer, but also the healthy life expectancy was longer and the proportion of individuals with healthy life expectancy was also higher. Qiao X C et al. [32] compared and analyzed the population health indicators among 31 provinces in China and found that the health level of elderly individuals who were socioeconomically advantaged was significantly higher than that of elderly individuals who were disadvantaged. China has long had a dual benefits structure for urban and rural areas. The level of rural health services is lower than that of cities, and the medical facilities are relatively poor, making it difficult to provide relatively sound health and medical services for elderly individuals. Elderly individuals with low incomes cannot flexibly use various health resources, strategies and channels, are limited by economic conditions and are prone to the phenomenon of "minor diseases not treated". Thus, the pursuit of a healthy quality of life is low.
Conventional wisdom holds that the less educated elderly individuals are, the less able they are to understand health-related knowledge. Thus, they cannot make timely and effective responses to health-related problems, resulting in poor health. However, this study found that the average life expectancy and healthy life expectancy of elderly individuals with low education levels are longer, and the proportion of healthy life expectancy is relatively low, which is consistent with the results of Jiao K S et al. [33]. However, contrary to the conclusions of most studies, Wu B Y et al. [34] used ADLs as an indicator to measure the healthy life expectancy of elderly individuals in China and found that the average life expectancy and healthy life expectancy of elderly individuals with higher education levels were longer, but the proportion of healthy life expectancy was relatively low. Elderly individuals with low education levels are mostly physical laborers, and their physical function is relatively good. Thus, they expect their health to continue for a relatively long time. Due to the limitations of income, elderly individuals with low levels of education have a lower functional recovery rate and a higher risk of death; their unhealthy survival period is relatively short, and their healthy life expectancy and proportion are higher than those of elderly individuals with high education levels.
The advantage of this study is that it adopts prospective cohort studies, and for the first time uses intrinsic capacity as an indicator to measure the health of the elderly population by measuring healthy life expectancy, using intrinsic capacity as a framework for assessing and monitoring the health of elderly individuals.. Different from the previous concept of discussing health by the presence of diseases, this perspective pays more attention to the function of elderly individuals and measures the healthy life expectancy of the elderly population with intrinsic capacity. This forms a new health standard by which to measure healthy life expectancy and expands the theoretical framework of health evaluation connotation. Further, we used the multistate life table method to measure and analyze the difference in the healthy life expectancy of the elderly population at different social levels, which not only reflects the changes in the health status of the elderly population but also provides a reference for the formulation of national policies. The study was also flawed. First, intrinsic capacity reflects the overall function of the body and mind, and a reasonable scoring method can better reflect the functional level of elderly individuals and enhance the comparability of different research results. However, the "Guidelines for Integrated Care for the Elderly" do not give a clear scoring method, and the scoring method of intrinsic capacity is still in the exploratory stage. In this study, only the integrity of intrinsic capacity was used as a health criterion for the elderly population, and the decline in intrinsic capacity was considered an unhealthy criterion. Therefore, how to translate each individual function into the scoring method for overall intrinsic capability needs further exploration. Second, older persons are a special group, and existing social stratification standards have certain limitations for them. For example, most people aged 60 and older have withdrawn from the labor market or have become inactive. Therefore, whether the economic income level of the elderly population can become the criterion for social stratification needs further confirmation.