Temporal Trends in Incidence of Dementia in a Birth Cohorts Analysis of the Framingham Heart Study

TL;DR

This study re-examines dementia incidence trends over four decades using advanced multistate modeling in the Framingham Heart Study, finding no decline in risk but higher risks for women, emphasizing improved analytical methods.

Contribution

It introduces a multistate modeling framework tailored for interval-censored data to accurately assess dementia trends across birth cohorts.

Findings

No decline in dementia risk across cohorts.

Women have higher lifetime dementia risks than men.

Multistate modeling improves trend estimation accuracy.

Abstract

Background: Dementia leads to a high burden of disability and the number of dementia patients worldwide doubled between 1990 and 2016. Nevertheless, some studies indicated a decrease in dementia risk which may be due to a bias caused by conventional analysis methods that do not adequately account for missing disease information due to death. Methods: This study re-examines potential trends in dementia incidence over four decades in the Framingham Heart Study. We apply a multistate modeling framework tailored to interval-censored illness-death data and define three non-overlapping birth cohorts (1915-1924, 1925-1934, and 1935-1944). Trends are evaluated based on both dementia prevalence and dementia risk, using age as the underlying timescale. Additionally, age-conditional dementia probabilities stratified by sex are estimated. Results: A total of 731 out of 3828 individuals were diagnosed with dementia. The multistate model analysis revealed no temporal decline in dementia risk across birth cohorts, irrespective of sex. When stratified by sex and adjusted for education, women consistently exhibited higher lifetime age-conditional risks (46%-50%) than men (30%-34%) over the study period. Conclusions: We recommend using a combination of multistate approach and separation into birth cohorts to adequately estimate trends of disease risk in cohort studies as well as to communicate patient-relevant outcomes such age-conditional disease risks.