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Declines in heart disease and stroke mortality rates are conventionally attributed to reductions in cigarette smoking, recognition and treatment of hypertension and diabetes, effective medications to improve serum lipid
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Declines in heart disease and stroke mortality rates are conventionally attributed to reductions in cigarette smoking, recognition and treatment of hypertension and diabetes, effective medications to improve serum lipid levels and to reduce clot formation, and general lifestyle improvements. Recent evidence implicates these and other cerebrovascular factors in the development of a substantial proportion of dementia cases. Analyses were undertaken to determine if corresponding declines in age-specific prevalence and incidence rates for dementia and cognitive impairment have occurred in recent years. Data spanning 1 or 2 decades were examined from community-based epidemiologic studies in Minnesota, Illinois, and Indiana, and from the Health and Retirement Study, a national survey. Although a marginal decline was observed in the Minnesota cohort, no clinically significant trends were apparent in the community studies. A significant reduction in cognitive impairment measured by neuropsychological testing was identified in the national survey. Cautious optimism appears justified.
Life expectancy has increased dramatically over the past century across the globe. This salutary trend unfortunately also has a negative aspect in that common chronic diseases of older people are becoming much more prevalent. The number of people affected by Alzheimer’s disease (AD) was 26.6 million worldwide in 2006, and it was estimated that $156 billion is spent annually to care for dementia patients worldwide. By 2050, the prevalence is expected to quadruple, so that 1 in 85 persons will be living with the disease, and 43.0% of them are expected to need a high level of care (e.g., a nursing home). Although the prevalence of dementia and its associated disability increases exponentially with age [4–6], the focus of research has recently shifted towards younger persons and the early stages of cognitive decline and mild cognitive impairment (MCI). The hope is to discover pathogenetic mechanisms underlying dementia and to delay the conversion of cognitive decline and MCI to full dementia. Indeed, if interventions could delay disease onset or progression by as little as 1 year, nearly 9.2 million fewer AD patients would be expected by the year 2050.
Dementia and AD represent a significant public health challenge for US society and one that is only likely to increase as the population ages. For example, there has been a large increase in diagnosis of AD on US death certificates in the last 10 years. However, it is important to separate increases in death certificate diagnoses due to growing awareness of the disease from increases due to changes in disease occurrence or mortality. Epidemiologists have attempted to uncover a wide range of risk and protective factors for dementia. Advocacy and public health organizations have also made efforts over the last 3 decades to increase the awareness of dementia and its known risk factors among both the public and practicing physicians. Thus far, these efforts have likely altered the risk of dementia only modestly, if at all. Society’s investment in dementia research must eventually be justified by progress made towards reducing the incidence of dementia or at least its associated disability.
Based on the time trends in potential risk and protective factors for cognitive impairment, there are good reasons to expect a decline in the incidence rates of cognitive impairment over time. However, there are also some trends in cardiovascular risk factors that would suggest an expected increase. A cluster of demographic, lifestyle, and medical factors have been identified which appear to alter the risk of developing dementia [8,9]. Prominent amongst these are vascular risk factors, including hypertension and diabetes [10,11]. Because cardiovascular disease and cerebrovascular disease contribute to the risk of dementia, and because there has been a substantial decline in the incidence of stroke in the last 50 years, some decline also in the risk of dementia might be expected. Alternatively, improved survival after stroke, or an increased prevalence of subclinical vascular disease in the absence of overt stroke, might result in more individuals in the population with increased risk of dementia.
New medications and other therapies for cardiovascular disease introduced since the early 1990s (e.g., wider use of antihypertensive and statin medications) may have contributed to a reduction in myocardial infarction and stroke over the past 20 years [12,13]. While the likelihood of treating hypertension and diabetes has increased, so also has the prevalence of these 2 conditions. From 1994 to 2002, in African-Americans over age 65 years, the prevalence of hypertension climbed from 73.0% to 83.0%, and the prevalence of diabetes rose from 26.0% to 36.0% [14,15]. The increased prevalence of hypertension, diabetes, and obesity may have contributed to an increased risk for cognitive decline and dementia, although the negative impact on brain health of diabetes and obesi