http://www.medscape.com/viewarticle/807966?src=wnl_edit_specol&uac=107573PV
Dementia prevalence in older people may be dropping. A new study that compared estimated dementia rates across 3 geographic areas in the United Kingdom (UK) in 12 groups 20 years apart shows that the actual prevalence of dementia was 24% lower than expected in the later group.
The results indicate that the older population may be getting healthier, said author Carol Brayne, MD, professor, public health medicine, University of Cambridge, UK, told Medscape Medical News. "It does suggest that all the preventive actions that are going on in midlife and early life are very important. It reinforces the message that having a healthy and active lifestyle is not only good for the heart, but is probably good for the brain, too."
The study was published online July 16 in The Lancet. Some of the data were also presented in Boston at the Alzheimer's Association International Conference (AAIC) 2013 by Fiona Matthews, Medical Research Council Biostatistics Unit, University Fourvie Site, Cambridge, United Kingdom.
Phase Integration
The analysis included the UK Cognitive Function and Ageing Study (CFAS) I, which estimated dementia prevalence in a sample of the population aged 65 and older in Cambridgeshire, Newcastle, and Nottingham, where interviews were conducted from 1990 to 1993. Researchers compared data from this study to those from CFAS II, which involved interviews with participants of the same age and in the same geographic areas but 20 years later, from 2008 to 2011.
The designs of CFAS I and CFAS II were identical, and for both, trained interviewers visited residences up to 3 times. In CFAS I, 7635 residents were interviewed; in CFAS II, 7796 were interviewed.
However, the CFAS I was a 2-stage study whereas CFAS was 1-stage. The CFAS I baseline interview included questions about sociodemographic characteristics, health, day-to-day function, social contacts, cognitive function, and medication. A random sample of 20% of those who had a baseline interview — stratified to represent the entire cognitive spectrum — was invited for assessment with the geriatric mental state (GMS) examination, a standardized interview designed to identify dementia and other psychiatric disorders in older people.
Rather than clinical classifications, assessments on both occasions used the same algorithmic approach to diagnoses, to provide consistency and reasonable validity across areas and time, she said.
The study found a substantial decrease in prevalence of dementia (odds ratio [OR] in CFAS II vs CFAS I: 0.7 [95% confidence interval], 0.6 - 0.9]; P=.003, adjusted in part for age, sex, and area). Women had a consistently higher dementia prevalence than men.
The overall decrease was driven by noncare settings and was not apparent within care settings where the prevalence increased (OR, 1.7). In CFAS I, the number of people with dementia in care setting represented 34% of all dementia cases; in CFAS II, the proportion of the population with dementia living in care was 29%.
The growing percentage of dementia cases living in the community might call for health policy changes to address a growing need for support, and for primary care physicians to be sensitive to their needs, said Dr. Brayne.
Using prevalence estimates from CFAS I in 1991, 664,000 individuals in the United Kingdom were expected to have dementia at that time. Taking into account the effects of population aging, this number would now be expected to be 884,000, but CFAS II puts the number in 2011 at 670,000, or a reduction of 24%.
The researchers found only slight, nonsignificant geographic variation in both CFAS I and CFAS II, but there were strong deprivation effects. A deprivation index uses census data on unemployment, car ownership, home ownership, and household overcrowding for a particular locality.
"If you look at the map of the projections, taking deprivation into account and using the age-sex profile of each of the areas, you do get quite varying prevalence expected in each of the areas across England," said Dr. Brayne.
Highest Areas
The dementia prevalence seems to be highest in areas with older age profiles as well as a high rate of deprivation, she added. "There are areas where the estimates go right up, particularly for men; in some areas, men's estimates get to be towards that for women."
Although the study didn't look at the causes of the decline in dementia, Dr. Brayne speculated that it reflects the benefits of primary prevention — managing hypertension, smoking cessation, better diet, and other lifestyle changes — that have also resulted in a dramatic drop in mortality from stroke and heart disease. Higher education levels, too, may have provided a protective effect, she added.
"All these things caused a 'cohort' effect, so in this cohort coming through now, the good things seem to be outweighing the bad things," which include more diabetes and cognitive side effects of stroke survival.
Policy changes over the 20 years between studies, which made it more difficult to access data, and a lower response rate for the second CFAS (56% compared with 80% in the earlier study) that may reflect a reluctance of family members to allow their loved ones to be interviewed, created some barriers for CFAS II, said Dr. Brayne.
"We will be doing formal analyses of nonresponses because we think it's a very important societal change. With some studies back in the 1980s, there was a 95% response rate."
In a statement from The Lancet, Editor-in-Chief Richard Horton said, "A reduction in prevalence of dementia in the older population is an important and welcome finding. But it is not a signal for the government to deprioritise investment in dementia care and research. Dementia remains a substantial challenge for those affected, their families, the NHS, and the Treasury.
"We need to understand better why the prevalence of dementia has fallen, and what that means for prevention and treatment services," Dr. Horton adds. "Sadly, dementia care and research are too often neglected and underfunded in the UK."
Commenting in an accompanying editorial, Sube Banerjee, MD, professor, mental health and ageing, King’s College, London, United Kingdom, said the study findings are "unequivocally good news."
He agreed that the study seems to support the idea that changes in health behavior have prevented or delayed the onset of dementia at a population level. "The next questions must be: how much further can we go in pursuit of this preventive agenda? How many more cases can be prevented? What do we need to do to have the greatest effect? These questions need empirical investigation followed by purposeful strategy formulation and implementation."
The notion that lifestyle changes, for example in diet, exercise, and smoking habits, might reduce the risk for dementia and promote more general health and well-being should be incorporated into health promotion messaging, said Dr. Banerjee.
But although it's a message of empowerment, it comes with a warning, he added. If positive changes in health behavior can decrease the prevalence of dementia, then negative lifestyle choices might promote, rather than prevent, dementia. "It is plausible that the present epidemic of morbid obesity, with consequent cardiovascular disorders, stroke, and diabetes, might act to increase the proportion of people with dementia in future cohorts."
The new data do not mean that dementia should be any less of a priority. Dementia remains "very common, very expensive, and profoundly negative" in its effects on patients and their families, said Dr. Banerjee. "Even with a small decrease in incidence and prevalence, population aging will still double the numbers with dementia worldwide in the next generation."
Numbers Still Up
Weighing in on the possible implications of these lowered dementia estimates, Mathew Baumgart, senior director of public policy, Alzheimer's Association, said that just because dementia estimates fall short of projections doesn't mean that the numbers aren't going up.
"Notwithstanding all the details and minutiae of this study, I think it confirms that we have a growing problem," he said. "The current prevalence estimate in this UK study is lower than what the projection would have been 20 years ago had they made a projection 20 years ago, but the actual prevalence is higher and therefore the stress and burden on the health care system and society are still greater."
According to the Alzheimer's Association, 5 million Americans aged 65 and over currently live with Alzheimer's disease, and that number will increase to 13.8 million by the year 2050.
Although the UK study adjusted only for age and gender, the models used to develop the U.S. projections also take into account other factors, such as the changing racial and ethnic composition of the population, mortality rates, and educational attainment, said Baumgart.
But he doesn't see any discrepancy between the two. "The issue is how do you measure what happens in the future and what are the factors that go into what's going to happen in a projection in the future, and both of these models are showing higher numbers."
In a statement, the Alzheimer's Association reiterates this point. While many older and middle aged people are now undertaking potentially brain-healthy but unproven steps, such as increased access to healthcare and increased physical and mental activity, whether that is actually affecting how many get dementia, "we simply do not know yet."
"However, even if the percentage of new cases in the population is going down (and we don't know for certain that it is) because the older population is growing at such a fast rate, dementia prevalence - that is, the total number of people with the disease - is continuing to rise. In other words, it is likely that prevalence is not going down but it could be increasing at a slightly slower pace," the statement notes.
This particular study used different methods from those in current prevalence studies in the United States, and it is not expected to have implications for dementia prevalence estimates in the United States, the statement adds.
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