Temporal trend in dementia incidence since 2002 and projections for prevalence in England and Wales to 2040: modelling studyBMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j2856 (Published 05 July 2017) Cite this as: BMJ 2017;358:j2856
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Ahmadi-Abhari et al1 forecasted dementia prevalence with a dynamic modelling approach that integrates calendar trends in dementia incidence with those for mortality and cardiovascular disease. They observed that despite the decrease in incidence and age specific prevalence, the number of people with dementia was projected to increase to 872 000, 1 092 000, and 1 205 000 in 2020, 2030, and 2040, respectively. The number of people with dementia in England and Wales is likely to increase by 57% from 2016 to 2040. This increase is mainly driven by improved life expectancy.
It is a good news that the incidence and age specific prevalence decreased. Why did it occured? Cardiometabolic syndrome consisting of obesity, dyslipidemia of high triglycerides or low high-density lipoprotein cholesterol, pre-hypertension, and pre-diabetes showing fasting glucose >100 mg/dl are major risk factor for cardiovascular diseases (CVD) such as hypertension, diabetes mellitus, coronary heart disease, and heart failure as well as cancer, congenital malformations, and dementia. Obesity is the most important factor among others and also can be controlled by diet and physical activity.2-4 Indeed, physical activity and many drug interventions are often potentially similar in terms of their mortality benefits in the secondary prevention of coronary heart disease, rehabilitation after stroke, treatment of heart failure, and prevention of diabetes.5 This study points the importance of therapeutic life style changes compared with drugs intervention.
Also, nowadays to control dyslipidemia of high low-density lipoprotein cholesterol, triglycerides or low high-density lipoprotein cholesterol, hypertension, and diabetes becomes possible with some drug interventions confirmed in a large scaled randomized clinical trials.6 To take these confirmed drugs and to perform therapeutic life style changes with diet and physical activity would expect to cut-off the incidence and age specific prevalence of dementia to a greater extent.
1. Ahmadi-Abhari S, Guzman-Castillo M, Bandosz P, Shipley MJ, Muniz-Terrera G, Singh-Manoux A, Kivimäki M, Steptoe A, Capewell S, O'Flaherty M, Brunner EJ. Temporal trend in dementia incidence since 2002 and projections for prevalence in England and Wales to 2040: modelling study. BMJ. 2017;358:j2856.
2. Koh KK. To take or not to take drugs? That is the question. BMJ 2013, Published 30 December 2013, http://www.bmj.com/content/347/bmj.f5577/rr/679697
3. Koh KK. Reconfirm to follow guidelines to prevent cardiovascular diseases. BMJ 2016, Published on 5 March 2016, http://www.bmj.com/content/352/bmj.i721/rr-0.
4. Kim SH, Després JP, Koh KK. Obesity and cardiovascular disease: friend or foe? Eur Heart J. 2016;37:3560-3568.
5. Naci H, Ioannidis JPA. Comparative effectiveness of exercise and drug interventions on mortality outcomes: metaepidemiological study. BMJ 2013;347:f5577
6. Koh KK. Letter by Koh Regarding Article, “Predicting the 10-Year Risks of Atherosclerotic Cardiovascular Disease in Chinese Population: The China-PAR Project (Prediction for ASCVD Risk in China)” and “Distribution of Estimated 10-Year Risk of Recurrent Vascular Events and Residual Risk in a Secondary Prevention Population”. Circulation. 2017;135:e818-e819.
Competing interests: No competing interests
Could cohort composition be driving this? Re: Temporal trend in dementia incidence since 2002 and projections for prevalence in England and Wales to 2040: modelling study
Ahmadi-Abhari and coauthors are to be congratulated for a timely and methodologically sophisticated work on past trend and future projection of dementia in England. In such an accomplished work results are bound to be nuanced. Although the future numbers of people with dementia are likely to increase in concert with life expectancy, the age specific prevalence is likely to decrease. This trend entails cost implications, and we will be better prepared to make the necessary allocation were we to have some idea as to the drivers of reduced prevalence.
Using the same English Longitudinal Study of Ageing 2002–2013 with joint model, I identified a comparable trend and found a new driver: delayed onset of cognitive impairment and cohort effect (1). The projected reduced prevalence in these authors’ new work is likely driven by delayed onset of dementia among the younger (post-War) cohort alive today and will increase in preponderance in future. Some evidence of precisely this delayed onset has recently arrived from across the pond thanks to a sister study to the English one, the US Health and Retirement Study. Over the last decade, dementia onset in older Americans has been delayed from an average age of 80.7 to one of 82.4 years (2, 3). This delayed onset has been posited on this side of the Atlantic (1, Figure 4).
But can we say more? Recent results comparing cohort effects on both sides of the Atlantic suggest a positive answer. We estimated that the three cohorts composing older people today (pre-War, War, and post-War) followed markedly different trajectories in each of the two countries which can be consequential for trends in health outcomes (4). Importantly, we found that the War cohort in America have better mental health trajectories than the English War cohort. (The other two cohorts are broadly similar: the pre-War cohorts in both countries are relatively similar to each other, likewise the post-War cohorts). Moreover, mental health of the English study members, as well as their gait speed and cognitive function have been shown to be significantly influenced by their childhood or cohort conditions (5). In sum, cohort effect shapes trends in dementia prevalence and onset in both countries. Since dementia onset in America has been found to be markedly delayed, and cohort composition in America is advantageous, it is likely that dementia onset in England will be delayed by at most the same amount. Future cost models of dementia burden may benefit from such a reasoned estimate.
1. Tampubolon. 2015. Cognitive ageing in Great Britain in the new century: Cohort differences in episodic memory. PLoS One. 10(12): e0144907 DOI: 10.1371/journal.pone.0144907
2. Crimmins et al. 2016. Change in cognitively healthy and cognitively impaired life expectancy in the United States: 2000–2010. SSM – Population Health. DOI: 10.1016/j.ssmph.2016.10.007
3. Kolata. 2016. U.S. dementia rates are dropping even as population ages. The New York Times. 21 November 2016. https://www.nytimes.com/2016/11/21/health/dementia-rates-united-states.html. Accessed: 19 July 2017.
4. Tampubolon and Maharani. 2017. When did old age stop being depressing? Depression trajectories of older Americans and Britons 2002-2012. American Journal of Geriatric Psychiatry. DOI: 10.1016/j.jagp.2017.06.006
5. Tampubolon. 2015. Growing up in poverty, growing old in infirmity: The long arm of childhood conditions in Great Britain. PLoS One. 10 (12): e0144722 DOI: 10.1371/journal.pone.0144722
Competing interests: No competing interests