Incidence of Dementia and Cognitive Impairment, Not Dementia in the United States

Objective: Estimates of incident dementia, and cognitive impairment, not dementia (CIND) (or the related mild cognitive impairment) are important for public health and clinical care policy. In this paper, we report US national incidence rates for dementia and CIND. Methods: Participants in the Aging, Demographic, and Memory Study (ADAMS) were evaluated for cognitive impairment using a comprehensive in-home assessment. A total of 456 individuals aged 72 years and older, who were not demented at baseline, were followed longitudinally from August 2001 to December 2009. An expert consensus panel assigned a diagnosis of normal cognition, CIND, or dementia and its subtypes. Using a population-weighted sample, we estimated the incidence of dementia, Alzheimer disease (AD), vascular dementia (VaD), and CIND by age. We also estimated the incidence of progression from CIND to dementia. Results: The incidence of dementia was 33.3 (standard error [SE], 4.2) per 1,000 person-years and 22.9 (SE, 2.9) per 1,000 person-years for AD. The incidence of CIND was 60.4 (SE, 7.2) cases per 1,000 person-years. An estimated 120.3 (SE, 16.9) individuals per 1,000 person-years progressed from CIND to dementia. Over a 5.9-year period, about 3.4 million individuals aged 72 and older in the United States developed incident dementia, of whom approximately 2.3 million developed AD, and about 637,000 developed VaD. Over this same period, almost 4.8 million individuals developed incident CIND. Interpretation: The incidence of CIND is greater than the incidence of dementia, and those with CIND are at high risk of progressing to dementia, making CIND a potentially valuable target for treatments aimed at slowing cognitive decline. ANN NEUROL 2011;70:418-426