This study examined the prevalence and pattern of multimorbidity in older adults by age, sex, and residence level based on a large national dataset in China. It can be seen that chronic disease and multimorbidity among older Chinese is a common public health issue. This study consists of 13 relative comprehensive chronic disease conditions including physical and mental illnesses, which are a reliable basis for exploring chronic diseases and their multimorbidity patterns. The finding indicated that 74.4% of the population had at least one of the 13 diseases and 42.4% suffered from multimorbidity, which was comparable to the results of a previous study [15]. The estimated prevalence of multimorbidity in this study is much lower than previous studies in other countries. For example, a study of 6101 older people in Irish showed a high prevalence of multimorbidity of 73.3% [16]. However, it is difficult to compare the prevalence rates generated by different studies due to differences in the types of diseases selected and the number of multimorbidities and the demographic characteristics of the samples.
Our study further assessed the multimorbidity patterns by age group, especially for aged 90 years and above that have not been mentioned in other studies. Some studies on multimorbidity have indicated that multimorbidity rates increase with age [17–18]. It is interesting that the prevalence of multimorbidity increased with age (43.1% older adults aged 65- 79 years and 48.2% for aged 80- 89 years), but no longer increased, and conversely, was lowest for longevity older adults aged 90- 117 years (36.4%). A Taiwanese cross-sectional study was similar to our results on multimorbidity trends in different age groups (53.1% vs. 64.3% vs. 45.7%) [19]. Besides, a study based on multi-country population indicated that South Africa showed a unique pattern with a gradual decline in the prevalence of multimorbidity in adults with the age of over 65 years old. Poland, as well as Mexico, also began to see a decline in the rate of multimorbidity in people aged 70 years and older [20]. This discrepancy is likely associated with the relatively large proportion of the population over 90 years of age (32.1%) in our study, and the lower prevalence of chronic and multiple diseases in these older adults, which contributed to this difference. It is also possible that older adults with multiple chronic conditions may have died or were unwilling to participate in the study. In addition, many participants aged 90 years or older did not even have access to a definitive diagnosis of a chronic disease due to financial and mobility constraints. By measuring the psychological status of older adults, we found that the rate of depression in older adults increases with age. Many existing studies have also included psychological disorders such as depression in the study of multiple diseases and studies have shown a bidirectional association between depression and multimorbidity. Multiple disorders and geriatric depression may also accelerate the processes of [21–22]. Future studies should investigate the role of depression in the association with clusters of multimorbid chronic diseases. In our study, the 65-79 years older adults had the highest prevalence of the hypertension-diabetes, which was trending younger. Recent studies have shown that the disease burden of diabetes in China is serious and there is an urgent need for greater intervention [23]. The slight gender differences found in this study regarding the multimorbidity of chronic diseases are consistent with van den et al [24]. All combinations of rheumatoid arthritis and visual impairment were more common in women, whereas stroke and respiratory diseases were more common in men, suggesting that a gender-specific disease spectrum for chronic disease management should be constructed for chronic disease control and intervention. We also found that the prevalence of multimorbidity was higher in the urban than those in rural, contrary to the results of another national study [25]. This may be due to the difference in the sample size of our study and the proportion of the population in urban and rural areas. Also, multimorbidity in the most socioeconomically deprived areas might occur 10-15 years earlier and 11-fold higher odds of physical and mental health disorders than those in affluent areas [18, 26]. The relatively low prevalence in our study, with the exception of depression, may represent a rural under-diagnosis in these rural communities with low awareness of the disease and limited access to laboratory testing. However, the diagnosis of depression, which was based on ten questions face-to-face, increased the diagnosis of the disease. This underscores the need to focus our capacity building efforts in these areas.
We observed that among participants with ≥2 chronic conditions, hypertension was present in almost all common multimorbidity patterns in different subgroups, as well as in the association rule results. One study by Ju-Hee Lee showed that the number of patients with hypertensive multimorbidities increases every year and grows more rapidly in older patients [27]. This strengthened the need for the prevention of hypertension to start long before the age of 65. The top 5 chronic diseases in terms of multimorbidity in this study were dyslipidemia, biliary disease, nervous system disease, diabetes, and stroke or CVD. Results also showed that although the prevalence of dyslipidemia is the ninth highest of the 13 chronic diseases, it has the highest multimorbidity rate, which means that older people with dyslipidemia are at great risk of having other complications. There are common behavioral risk factors among the diseases, e.g., poor dietary habits are risk factors for diabetes and can also lead to cardiovascular disease, hitting upon the need for change poor lifestyle before the age of 65 [11]. In contrast, depression, which has the second highest prevalence rate in the entire population, has the lowest multimorbidity rate. This suggests that depression can also develop alone without other chronic conditions.
The greatest strength of this study is the adequate size and representative sample to investigate the multimorbidity patterns among the Chinese older population living in longevity areas. This study also had several limitations. Firstly, this article used cross-sectional data, which cannot observe the complexly changing relationship between multiple chronic diseases. Secondly, our study did not dig into the factors influencing multimorbidity, and further research is needed to investigate the influencing factors related to multimorbidity.