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Is the risk of Alzheimer’s disease and dementia declining?

Alzheimer's Research & Therapy

BioMed Central

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      Abstract

      Background

      The number of older adults with dementia will increase around the world in the decades ahead as populations age. Current estimates suggest that about 4.2 million adults in the US have dementia and that the attributable economic cost of their care is about $200 billion per year. The worldwide dementia prevalence is estimated at 44.3 million people and the total cost at $604 billion per year. It is expected that the worldwide prevalence will triple to 135.5 million by 2050. However, a number of recent population-based studies from countries around the world suggest that the age-specific risk of dementia may be declining, which could help moderate the expected increase in dementia cases that will accompany the growing number of older adults.

      Discussion

      At least nine recent population-based studies of dementia incidence or prevalence have shown a declining age-specific risk in the US, England, The Netherlands, Sweden, and Denmark. A number of factors, especially rising levels of education and more aggressive treatment of key cardiovascular risk factors such as hypertension and hypercholesterolemia, may be leading to improving ‘brain health’ and declining age-specific risk of Alzheimer’s disease and dementia in countries around the world.

      Summary

      Multiple epidemiological studies from around the world suggest an optimistic trend of declining population dementia risk in high-income countries over the past 25 years. Rising levels of education and more widespread and successful treatment of key cardiovascular risk factors may be the driving factors accounting for this decline in dementia risk. Whether this optimistic trend will continue in the face of rising worldwide levels of obesity and diabetes and whether this trend is also occurring in low- and middle-income countries are key unanswered questions which will have enormous implications for the extent of the future worldwide impact of Alzheimer’s disease and dementia on patients, families, and societies in the decades ahead.

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      Most cited references 18

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      US trends in prevalence, awareness, treatment, and control of hypertension, 1988-2008.

      Hypertension is a major risk factor for cardiovascular disease and treatment and control of hypertension reduces risk. The Healthy People 2010 goal was to achieve blood pressure (BP) control in 50% of the US population. To assess progress in treating and controlling hypertension in the United States from 1988-2008. The National Health and Nutrition Examination Survey (NHANES) 1988-1994 and 1999-2008 in five 2-year blocks included 42 856 adults aged older than 18 years, representing a probability sample of the US civilian population. Hypertension was defined as systolic BP of at least 140 mm Hg and diastolic BP of at least 90 mm Hg, self-reported use of antihypertensive medications, or both. Hypertension control was defined as systolic BP values of less than 140 mm Hg and diastolic BP values of less than 90 mm Hg. All survey periods were age-adjusted to the year 2000 US population. Rates of hypertension increased from 23.9% (95% confidence interval [CI], 22.7%-25.2%) in 1988-1994 to 28.5% (95% CI, 25.9%-31.3%; P < .001) in 1999-2000, but did not change between 1999-2000 and 2007-2008 (29.0%; 95% CI, 27.6%-30.5%; P = .24). Hypertension control increased from 27.3% (95% CI, 25.6%-29.1%) in 1988-1994 to 50.1% (95% CI, 46.8%-53.5%; P = .006) in 2007-2008, and BP among patients with hypertension decreased from 143.0/80.4 mm Hg (95% CI, 141.9-144.2/79.6-81.1 mm Hg) to 135.2/74.1 mm Hg (95% CI, 134.2-136.2/73.2-75.0 mm Hg; P = .02/P < .001). Blood pressure control improved significantly more in absolute percentages between 1999-2000 and 2007-2008 vs 1988-1994 and 1999-2000 (18.6%; 95% CI, 13.3%-23.9%; vs 4.1%; 95% CI, -0.5% to 8.8%; P < .001). Better BP control reflected improvements in awareness (69.1%; 95% CI, 67.1%-71.1%; vs 80.7%; 95% CI, 78.1%-83.0%; P for trend = .03), treatment (54.0%; 95% CI, 52.0%-56.1%; vs 72.5%; 95% CI, 70.1%-74.8%; P = .004), and proportion of patients who were treated and had controlled hypertension (50.6%; 95% CI, 48.0%-53.2%; vs 69.1%; 95% CI, 65.7%-72.3%; P = .006). Hypertension control improved significantly between 1988-1994 and 2007-2008, across age, race, and sex groups, but was lower among individuals aged 18 to 39 years vs 40 to 59 years (P < .001) and 60 years or older (P < .001), and in Hispanic vs white individuals (P = .004). Blood pressure was controlled in an estimated 50.1% of all patients with hypertension in NHANES 2007-2008, with most of the improvement since 1988 occurring after 1999-2000. Hypertension control was significantly lower among younger than middle-aged individuals and older adults, and Hispanic vs white individuals.
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        Potential for primary prevention of Alzheimer's disease: an analysis of population-based data.

        Recent estimates suggesting that over half of Alzheimer's disease burden worldwide might be attributed to potentially modifiable risk factors do not take into account risk-factor non-independence. We aimed to provide specific estimates of preventive potential by accounting for the association between risk factors. Using relative risks from existing meta-analyses, we estimated the population-attributable risk (PAR) of Alzheimer's disease worldwide and in the USA, Europe, and the UK for seven potentially modifiable risk factors that have consistent evidence of an association with the disease (diabetes, midlife hypertension, midlife obesity, physical inactivity, depression, smoking, and low educational attainment). The combined PAR associated with the risk factors was calculated using data from the Health Survey for England 2006 to estimate and adjust for the association between risk factors. The potential of risk factor reduction was assessed by examining the combined effect of relative reductions of 10% and 20% per decade for each of the seven risk factors on projections for Alzheimer's disease cases to 2050. Worldwide, the highest estimated PAR was for low educational attainment (19·1%, 95% CI 12·3-25·6). The highest estimated PAR was for physical inactivity in the USA (21·0%, 95% CI 5·8-36·6), Europe (20·3%, 5·6-35·6), and the UK (21·8%, 6·1-37·7). Assuming independence, the combined worldwide PAR for the seven risk factors was 49·4% (95% CI 25·7-68·4), which equates to 16·8 million attributable cases (95% CI 8·7-23·2 million) of 33·9 million cases. However, after adjustment for the association between the risk factors, the estimate reduced to 28·2% (95% CI 14·2-41·5), which equates to 9·6 million attributable cases (95% CI 4·8-14·1 million) of 33·9 million cases. Combined PAR estimates were about 30% for the USA, Europe, and the UK. Assuming a causal relation and intervention at the correct age for prevention, relative reductions of 10% per decade in the prevalence of each of the seven risk factors could reduce the prevalence of Alzheimer's disease in 2050 by 8·3% worldwide. After accounting for non-independence between risk factors, around a third of Alzheimer's diseases cases worldwide might be attributable to potentially modifiable risk factors. Alzheimer's disease incidence might be reduced through improved access to education and use of effective methods targeted at reducing the prevalence of vascular risk factors (eg, physical inactivity, smoking, midlife hypertension, midlife obesity, and diabetes) and depression. National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care for Cambridgeshire and Peterborough. Copyright © 2014 Elsevier Ltd. All rights reserved.
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          Changes in diabetes-related complications in the United States, 1990-2010.

          Preventive care for adults with diabetes has improved substantially in recent decades. We examined trends in the incidence of diabetes-related complications in the United States from 1990 through 2010. We used data from the National Health Interview Survey, the National Hospital Discharge Survey, the U.S. Renal Data System, and the U.S. National Vital Statistics System to compare the incidences of lower-extremity amputation, end-stage renal disease, acute myocardial infarction, stroke, and death from hyperglycemic crisis between 1990 and 2010, with age standardized to the U.S. population in the year 2000. Rates of all five complications declined between 1990 and 2010, with the largest relative declines in acute myocardial infarction (-67.8%; 95% confidence interval [CI], -76.2 to -59.3) and death from hyperglycemic crisis (-64.4%; 95% CI, -68.0 to -60.9), followed by stroke and amputations, which each declined by approximately half (-52.7% and -51.4%, respectively); the smallest decline was in end-stage renal disease (-28.3%; 95% CI, -34.6 to -21.6). The greatest absolute decline was in the number of cases of acute myocardial infarction (95.6 fewer cases per 10,000 persons; 95% CI, 76.6 to 114.6), and the smallest absolute decline was in the number of deaths from hyperglycemic crisis (-2.7; 95% CI, -2.4 to -3.0). Rate reductions were larger among adults with diabetes than among adults without diabetes, leading to a reduction in the relative risk of complications associated with diabetes. When expressed as rates for the overall population, in which a change in prevalence also affects complication rates, there was a decline in rates of acute myocardial infarction and death from hyperglycemic crisis (2.7 and 0.1 fewer cases per 10,000, respectively) but not in rates of amputation, stroke, or end-stage renal disease. Rates of diabetes-related complications have declined substantially in the past two decades, but a large burden of disease persists because of the continued increase in the prevalence of diabetes. (Funded by the Centers for Disease Control and Prevention.).
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            Author and article information

            Affiliations
            [ ]Division of General Medicine, University of Michigan Health System, 2800 Plymouth Road, Bldg 16, Room 430 W, Ann Arbor, MI 48109-0429 USA
            [ ]Veterans Affairs Center for Practice Management and Outcomes Research, 2215 Fuller Road, Ann Arbor, MI 48105 USA
            [ ]Institute for Social Research, University of Michigan, 426 Thompson Street, Ann Arbor, MI 48105 USA
            [ ]Institute of Gerontology, University of Michigan, 300 N. Ingalls Street, Ann Arbor, MI 48109 USA
            [ ]Institute for Healthcare Policy and Innovation, University of Michigan, 2800 Plymouth Road, Ann Arbor, MI 48109 USA
            Contributors
            klanga@umich.edu
            Journal
            Alzheimers Res Ther
            Alzheimers Res Ther
            Alzheimer's Research & Therapy
            BioMed Central (London )
            1758-9193
            26 March 2015
            26 March 2015
            2015
            : 7
            : 1
            4374373
            118
            10.1186/s13195-015-0118-1
            © Langa; licensee BioMed Central. 2015

            This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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