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Satizabal CL, Beiser AS, Chouraki V, Chêne G, Dufouil C, Seshadri S. Incidence of Dementia over Three Decades in the Framingham Heart Study. N Engl J Med. 2016 Feb 11;374(6):523-32. PubMed.
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University of Southern California Keck School of Medicine
The accumulating evidence for decreases in the age-specific incidence of Alzheimer disease or dementia, over fairly short periods of five to 10 years, encourages speculating that this may be due to environmental and public health improvements over the past half-century, and that the Flynn effect and Fries’ predictions of compression of morbidity may be in play. People may be getting smarter, stronger, bigger, and healthier; surviving longer, and pushing back illness and age-related conditions closer to the end of life.
It is tempting to consider that the cohorts who are benefiting were born in the early 20th century and suffered as children through a major flu epidemic, the effects of two world wars, the Great Depression, and periods of starvation and poverty. Then as survivors and adults—into the latter half of the century—they had relatively healthy and prosperous lives with improvements in diet, nutrition, hygiene, education, environmental pollution, automation, and overall quality of life. One might expect this trend to be further enhanced for the baby boomers born into relative and continuing prosperity.
The 22 percent to 44 percent reduction in risk or incidence over short, five- to 10-year periods is remarkably large and of the same magnitude as that expected in Alzheimer’s disease-prevention studies. If a 25 percent risk reduction were to be observed for a drug tested in a prevention clinical trial then we would be talking about a clinically meaningful effect as if it were a “cure.” Such drugs for prevention or for mild Alzheimer disease—if proven effective—will be very costly. For example, solanezumab may command an average wholesale price of about $4,500 per month or $54,000 per year, for a planned effect that is relatively small. Given the epidemiological data, one might wonder if CMS or Medicare would be willing to pay this amount to middle-aged and older beneficiaries for them to engage in further health-promotion activities. Although much more than an ounce of prevention, this public health intervention still might outweigh several thousand pounds of cure.
View all comments by Lon S. SchneiderCambridge University
We did a comprehensive analysis of the studies that have been comparable that have been published in Europe, with indications of stabilization or reduction in both prevalence and incidence (Wu et al., 2016). The Rotterdam study within that analysis is, like Framingham, a dynamic cohort with refreshment of younger cohorts, and it suggests incidence reduction. All incidence studies to date have been single-site comparisons across time within single countries. The Framingham and those emerging from France have also looked at the profile of risk across time.
There is growing evidence from the United States and Western Europe that dementia itself is changing as health and other life experience profiles change across generations.
There are more studies of incidence to come. We will need to know whether or not such patterns are confirmed in further, larger comparative studies that look across geographies (including low- and middle-income countries). Japan has not reported such changes for example, although it is possible that diagnostic drift could account for the observed increase in prevalence.
It certainly points to the fact that we should not assume that current dementia is the same as dementia in the past, nor will it be the same in the future. This is a shift in thinking compared to a decade ago, even though vascular factors were beginning to be re-recognized at that stage. This has implications for the nature of future dementia policy and research investment.
References:
Wu YT, Fratiglioni L, Matthews FE, Lobo A, Breteler MM, Skoog I, Brayne C. Dementia in western Europe: epidemiological evidence and implications for policy making. Lancet Neurol. 2016 Jan;15(1):116-24. Epub 2015 Aug 21 PubMed.
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