Brayne Carol, Gao Lu, Dewey Michael, Matthews Fiona E
Department of Public Health and Primary Care, Institute of Public Health, Cambridge University, Cambridge, United Kingdom.
PLoS Med. 2006 Oct;3(10):e397. doi: 10.1371/journal.pmed.0030397.
Dementia and severe cognitive impairment are very closely linked to ageing. The longer we live the more likely we are to suffer from these conditions. Given population increases in longevity it is important to understand not only risk and protective factors for dementia and severe cognitive impairment at given ages but also whether protection affects cumulative risk. This can be explored by examining the effect on cumulative risk by time of death of factors found consistently to reduce risk at particular ages, such as education and social status.
In this analysis we report the prevalence of dementia and severe cognitive impairment in the year before death in a large population sample. In the Medical Research Council Cognitive Function and Ageing Study (a 10-y population-based cohort study of individuals 65 and over in England and Wales), these prevalences have been estimated by age, sex, social class, and education. Differences have been explored using logistic regression. The overall prevalence of dementia at death was 30%. There was a strong increasing trend for dementia with age from 6% for those aged 65-69 y at time of death to 58% for those aged 95 y and above at time of death. Higher prevalences were seen for severe cognitive impairment, with similar patterns. People with higher education and social class had significantly reduced dementia and severe cognitive impairment before death, but the absolute difference was small (under 10%).
Reducing risk for dementia at a given age will lead to further extension of life, thus cumulative risk (even in populations at lower risk for given ages) remains high. Ageing of populations is likely to result in an increase in the number of people dying with dementia and severe cognitive impairment even in the presence of preventative programmes. Policy development and research for dementia must address the needs of individuals who will continue to experience these conditions before death.
痴呆症和严重认知障碍与衰老密切相关。我们活得越久，患这些疾病的可能性就越大。鉴于人口预期寿命的增加，不仅了解特定年龄阶段痴呆症和严重认知障碍的风险因素和保护因素很重要，而且了解保护因素是否会影响累积风险也很重要。这可以通过研究在特定年龄阶段持续发现的降低风险的因素（如教育程度和社会地位）对死亡时间的累积风险的影响来进行探索。
在本分析中，我们报告了一大群人样本在死亡前一年的痴呆症和严重认知障碍患病率。在医学研究委员会认知功能与衰老研究（一项针对英格兰和威尔士65岁及以上人群的为期10年的基于人群的队列研究）中，这些患病率已按年龄、性别、社会阶层和教育程度进行了估算。使用逻辑回归探讨了差异。死亡时痴呆症的总体患病率为30%。痴呆症患病率随年龄增长呈强劲上升趋势，从死亡时年龄在65 - 69岁的人群中的6%上升到死亡时年龄在95岁及以上人群中的5&。严重认知障碍的患病率更高，且模式相似。教育程度和社会阶层较高的人在死亡前患痴呆症和严重认知障碍的比例显著降低，但绝对差异较小（低于10%）。
在特定年龄降低痴呆症风险将导致寿命进一步延长，因此累积风险（即使在特定年龄风险较低的人群中）仍然很高。即使存在预防计划，人口老龄化也可能导致死于痴呆症和严重认知障碍人数的增加。痴呆症的政策制定和研究必须满足那些在死亡前仍将经历这些疾病的个体的需求。
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