Among a population aged 55 years or more who had high levels of cardiovascular risk, we found high dementia prevalence. Coupled with the fact that stroke, diabetes, hypertension and depression were significant risk factors, our observations were consistent with other studies 2,8, 23.
In our sample, the age- gender adjusted prevalence of dementia was 10.15%, which was about twice as high compared to the general population aged 65 or older in China (5.14%), according to the national epidemiological survey 2. It was also higher than that of the general population in Zhejiang province (4.9%), but lower than the nursing homes (40.6%) 19. The age- gender adjusted prevalence of MCI was 25.46%, which was also higher than that of the general population in Zhjiang province 2, 19.
Considering demographic factors, the prevalence of dementia and MCI were associated with increased age and decreased education levels, which was consistent with other studies 8, 24. Our study found a higher prevalence of dementia in men than women at high risk for CVD, but other studies had shown a higher prevalence of dementia in women than men among the general population 25.
To our knowledge, ours was one of very few surveys of dementia prevalence in a population at high risk of CVD. The prevalence of CVD risk factors of this study population was relatively high. Hypertension was present more than half of the study population, double of the global age standardized prevalence of hypertension 26. The mean total cholesterol (TC) of our study was 5.33 mmol/L, which was higher than that of the general population (4.63 mmol/L). The stroke prevalence of 4.0% was higher than that of 2.88% among the general Chinese population aged 40 years or more 27. Furthermore, the prevalence of regular exercises of 13.7% was relatively low, compared with that of 33.9% of Chinese residents 27. The smoking rate of nearly 30% among men in the study was high, while it was about 0.36% for women. And the high prevalence of alcohol abuse among men (more than half) was also of great concern and needed to be addressed.
Many factors had been associated with a risk for dementia. Consistent with previous investigations in China and other countries, our study confirmed that older age was a strong risk factor for dementia in populations at high risk of CVD 2, 22. Data of the survey showed that higher education including middle and high schooling were important protective factors for dementia, compared with illiteracy, which supported the view that more education could protect against the consequence of dementia 22, 28. Heavy drinking was a risk factor for dementia, which was confirmed by previous studies 2, 19. Prevalence of dementia had been found to be higher in women than men in some regions but not in all 18. In our survey, being female was a protective factor for dementia.
In addition, CVD including of diabetes, stroke and hypertension were important risk factors of dementia 22, 29. Other studies showed that persons with diabetes had an increased risk for dementia 18. Meanwhile, some studies showed that stroke increased the risk of dementia 30, 31 with most of cases were preventable 32, 33, and the medical history of hypertension might result in cognitive decline 34, 35. Reducing cardiovascular risk factors would be an effective way to reduce the dementia burden.
It should be mentioned that depression was a strong risk factor for dementia among this survey population. An association between depression and dementia had been suggested in at least 4 independent meta-analyses, indicating close to a 2-fold higher risk of developing dementia following depression 36–40, as well as several reviews 41, 42. Additionally, evidence suggested that cerebrovascular changes might constitute a link between depression and dementia. It was not only epidemiologically but also biologically plausible that depression increased dementia risk 34, 43. Further research was needed to investigate whether successful prevention and antidepressive treatment of depression decreased the risk of dementia
Some limitations needed to be mentioned in this study. This was a cross-sectional study, which made it difficult to establish a cause-and-effect relationship for risk factors. Furthermore, due to the limited conditions, imaging and other biological indicators could not be performed for every suspected case to precisely ascertain the dementia subtypes.
Despite these limitations, the strengths included that it was one of very few surveys about dementia prevalence among a population at high risk of CVD. Meanwhile, participants were assessed by trained physicians which made results reliable. And the study was a part of the PEACE Million Persons Project, which providing regional representative data at a population level in Zhejiang province.
In conclusion, cognitive impairment are highly prevalent among elderly at high risk of CVD in Zhejiang province, and it will be increasingly so in the years to come. The existing social supports should be used adequately, focusing on modifiable risk factors of dementia, such as cardiovascular risk factors, and making patients maintain a good psychological state to better prevent CVD and dementia. Meanwhile, more population-based strategies, including raising awareness and advocate for the development of health care and primary prevention policies to address this rapidly growing dementia epidemic and the high prevalence of cardiovascular risk factors are needed. In addition, the development of standardized dementia intervention programs should also be one of the next research priorities.