Incidence of Dementia over Three Decades in the Framingham Heart Study
BACKGROUND
The prevalence of dementia is expected to soar as the average life expectancy increases, but recent estimates suggest that the age-specific incidence of dementia is declining in high-income countries. Temporal trends are best derived through continuous monitoring of a population over a long period with the use of consistent diagnostic criteria. We describe temporal trends in the incidence of dementia over three decades among participants in the Framingham Heart Study.
METHODS
Participants in the Framingham Heart Study have been under surveillance for incident dementia since 1975. In this analysis, which included 5205 persons 60 years of age or older, we used Cox proportional-hazards models adjusted for age and sex to determine the 5-year incidence of dementia during each of four epochs. We also explored the interactions between epoch and age, sex, apolipoprotein E ε4 status, and educational level, and we examined the effects of these interactions, as well as the effects of vascular risk factors and cardiovascular disease, on temporal trends.
RESULTS
The 5-year age- and sex-adjusted cumulative hazard rates for dementia were 3.6 per 100 persons during the first epoch (late 1970s and early 1980s), 2.8 per 100 persons during the second epoch (late 1980s and early 1990s), 2.2 per 100 persons during the third epoch (late 1990s and early 2000s), and 2.0 per 100 persons during the fourth epoch (late 2000s and early 2010s). Relative to the incidence during the first epoch, the incidence declined by 22%, 38%, and 44% during the second, third, and fourth epochs, respectively. This risk reduction was observed only among persons who had at least a high school diploma (hazard ratio, 0.77; 95% confidence interval, 0.67 to 0.88). The prevalence of most vascular risk factors (except obesity and diabetes) and the risk of dementia associated with stroke, atrial fibrillation, or heart failure have decreased over time, but none of these trends completely explain the decrease in the incidence of dementia.
CONCLUSIONS
Among participants in the Framingham Heart Study, the incidence of dementia has declined over the course of three decades. The factors contributing to this decline have not been completely identified. (Funded by the National Institutes of Health.)
Supported by the National Heart, Lung, and Blood Institute Framingham Heart Study (contract no. N01-HC-25195 and no. HHSN268201500001I) and by grants from the National Institute on Aging (AG08122 and AG033193) and the National Institute of Neurological Disorders and Stroke (NS017950).
Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.
The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute on Aging, the National Institutes of Health, or the National Heart, Lung, and Blood Institute.
We thank the study participants, as well as the study team (especially the investigators and staff of the neurology team) for their contributions to data collection over the past four decades.
SOURCE INFORMATION
From the Boston University Schools of Medicine (C.L.S., A.S.B., V.C., S.S.) and Public Health (A.S.B.), Boston, and the Framingham Heart Study, Framingham (C.L.S., A.S.B., V.C., S.S.) — all in Massachusetts; and Inserm Unité 1219 and CIC 1401-EC (Clinical Epidemiology) and University of Bordeaux, ISPED (Bordeaux School of Public Health) — both in Bordeaux, France (G.C., C.D.).
Address reprint requests to Dr. Seshadri at the Boston University School of Medicine, Department of Neurology, 72 E. Concord St., B602, Boston, MA 02118, or at suseshad@bu.edu.
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