Prevalence and influencing factors of mild cognitive impairment and dementia in Chinese older adults: A community-based study

To the Editor: Dementia is a common degenerative disease characterized by a progressive decline in cognitive function and the ability to perform activities of daily living. In 2010, >35 million people worldwide were living with dementia, and this number is expected to increase to >115 million by 2050.[1] Mild cognitive impairment (MCI) is an intermediate state between normal aging and dementia, and it has a higher risk of transition to dementia.[2] Over the past few decades, >100 epidemiological studies have been conducted in China to investigate the prevalence of dementia and MCI and their influencing factors. Although these studies are helpful in understanding the pathogenesis of cognitive impairment, their prevalence estimates are highly inconsistent, resulting in unreliable results. These differences may be related to older age spans, inconsistent diagnostic criteria for dementia and MCI, and different assessment tools. To overcome these limitations, we performed a series of subgroup analyses. Our aims were to determine the prevalence of dementia and MCI among the elderly in the Chinese community and investigate the cross-sectional association of dementia/MCI with demographic characteristics, lifestyle, and clinical factors. This study was approved by the Ethics Committee of the Shanghai Mental Health Center (No. CRC2017ZD02-02). All participants provided written informed consent prior to the study. Data were obtained from the Brain Health Cohort study in Shanghai, which aimed to conduct baseline screening of the target population and investigate the prevalence of cognitive dysfunction and related cognitive influencing factors in the elderly in the Shanghai community. Finally, 2434 community participants aged ≥55 years participated. All participants completed a series of surveys regarding general demographic data, clinical assessments, and scale assessments. The diagnosis of dementia was based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition,[3] while the diagnosis of MCI was based on Petersen’s criteria.[4] Continuous variables are expressed as means ± standard deviations, and categorical variables are expressed as numbers and percentages. Next, the independent samples t test and the Chi-square test were used to compare continuous variables and categorical variables between MCI/dementia and normal groups, respectively. Finally, multivariable logistic regression models were used to examine the association of dementia and MCI with sociodemographic features, lifestyle, and clinical conditions. All statistical analyses were performed using SPSS (version 22.0; IBM Corporation, Armonk, NY, USA) and a two-tailed test with a significance level of P <0.05. The mean participants’ age was 69.30 ± 7.88 years, the average length of schooling was 10.54 ± 3.63 years, the average body mass index (BMI) was 23.70 ± 3.86 kg/m2, and 34.84% (848/2434) were male. The results are summarized in Supplementary Table 1, https://links.lww.com/CM9/C230. Among the 2434 participants, 197 (8.09%), 1000 (41.08%), and 1237 (50.82%) had dementia, MCI, and normal cognitive function, respectively. Next, we calculated the proportions of dementia and MCI among men and women, respectively. The proportion of dementia and MCI in men was 10.02% (85/848) and 38.09% (323/848), and the proportion of dementia and MCI in women was 7.06% (112/1586) and 42.69% (677/1586), respectively. However, when we used the Chi-square test followed by ‌Bonferroni test, we found no statistical difference in the proportion of dementia and MCI between men and women. After comparison between the dementia/MCI and the control group, those variables with P <0.05 were entered into the multivaribale analaysis [Supplementary Table 2, https://links.lww.com/CM9/C230]. Using the multivariable logistic regression analysis, we found that education (odds ratio [OR]: 0.901, 95% CI: 0.878–0.924, P <0.001), physical exercise (OR: 0.757, 95% CI: 0.629–0.913, P = 0.003), hyperlipidemia (OR: 0.813, 95% CI: 0.676–0.978, P = 0.028), and cerebral infarction (OR: 1.665, 95% CI: 1.313–2.112, P <0.001) were associated with MCI. Moreover, age (OR: 1.045, 95% CI: 1.020–1.070, P <0.001), education (OR: 0.923, 95% CI: 0.878–0.969, P = 0.001), BMI (OR: 0.905, 95% CI: 0.866–0.947, P <0.001), male sex (OR: 1.678, 95% CI: 1.136–2.477, P = 0.009), tea consumption (OR: 0.594, 95% CI: 0.405–0.873, P = 0.008), physical exercise (OR: 0.235, 95% CI: 0.141–0.394, P <0.001), hypertension (OR: 0.597, 95% CI: 0.410–0.870, P = 0.007), hyperlipidemia (OR: 0.608, 95% CI: 0.402–0.920, P = 0.019), and depression (OR: 5.956, 95% CI: 2.673–13.269, P <0.001) were associated with dementia [Table 1]. Table 1 - Possible influencing factors related to MCI or dementia analyzed by multivariable logistics regression analysis. Variables P OR 95% confidence interval MCI Age 0.238 1.007 0.995–1.019 Education <0.001 0.901 0.878–0.924 Tea consumption 0.065 0.848 0.712–1.010 Physical exercise 0.003 0.757 0.629–0.913 Hypertension 0.097 1.166 0.973–1.399 Coronary heart disease 0.094 1.235 0.965–1.581 Hyperlipidemia 0.028 0.813 0.676–0.978 Cerebral infarction <0.001 1.665 1.313–2.112 Dementia Age <0.001 1.045 1.020–1.070 Education 0.001 0.923 0.878–0.969 BMI <0.001 0.905 0.866–0.947 Males 0.009 1.678 1.136–2.477 Tea consumption 0.008 0.594 0.405–0.873 Physical exercise <0.001 0.235 0.141–0.394 Hypertension 0.007 0.597 0.410–0.870 Hyperlipidemia 0.019 0.608 0.402–0.920 Cerebral infarction 0.123 1.462 0.903–2.368 Depression <0.001 5.956 2.673–13.269 Family history of dementia 0.928 0.938 0.232–3.797 BMI: Body mass index; MCI: Mild cognitive impairment; OR: Odds ratio. The results of our study differed from those of a previous study[5] as we adopted a diagnostic method combining clinical evaluation and scales, which was different from the previous single-diagnosis mode. Second, the prevalence of dementia and MCI may have increased in recent years. Next, we explored the potential effects of sex on the development of dementia and MCI but did not find a statistical difference in the proportion of dementia or MCI between men and women. In addition, we found that BMI, hypertension and hyperlipidemia are associated with a lower risk of dementia, contrary to conclusions of previous studies,[6] which might be caused by the following reasons: first, the participants’ disease information was self-reported, which could have influenced the study results; second, we did not stratify the types of dementia, which could also have skewed the results. In conclusion, we found that education, physical exercise, and hyperlipidemia were associated with dementia and MCI. Moreover, cerebral infarction was associated with MCI. Finally, in addition to education, physical exercise, and hyperlipidemia, BMI, male, tea consumption, hypertension, and depression were associated with dementia. Therefore, we speculate that dementia and MCI are influenced by distinct factors, suggesting the need for tailored interventions based on the specific cognitive state. Funding This research was funded by the China Ministry of Science and Technology (No. STI2030-Major Projects-2022ZD0213100), National Natural Science Foundation of China (Nos. 82101564, 82001123, 82271607), Feixiang Program of Shanghai Mental Health Center (No. 2020-FX-03), Shanghai Clinical Research Center for Mental Health (No. 19MC1911100), Shanghai brain health foundation (No. SHBHF2016001), Chinese Academy of Sciences (No. XDA12040101), Shanghai Clinical Research Center for Mental Health (Nos. SCRC-MH, 19MC1911100), and Shanghai Science and Technology Committee (No. 20Y11906800). Conflicts of interest None.