Decline in Dementia Over 30 Years

Research Highlights

Dementia is one of the most prevalent and debilitating diseases among the elderly across the world. As the medical and technologic communities continue to innovate, average life expectancy keeps increasing. However, this calls for concern when it comes to diseases with onset at older ages. A long-term study in Framingham, Massachusetts observed individuals over an extended period of time to determine the incidence trend of dementia as people are expected to live longer.

            The study, named the Framingham Heart study, was initially started in 1948. 5209 Framingham residents were involved, which included examinations performed every 2 years. The examinations included a medical history, lab tests, and a physical exam. In 1971, 5214 offspring of the original participants, as well the spouses of this next generation, began an offspring study. While the original study held exams every 2 years, up to a total of 32 examinations, the offspring study delayed the exam intervals to every 4 years, with a maximum of 9 total exams.

            Beginning in 1975, cognitive status was monitored in the original study. An alternative group was created, which included dementia-free participants. After 1981, participants were assessed using the MMSE – Mini-Mental State Examination. The offspring study started undergoing MMSEs since 1991, with neuropsychological exams also being administered every 5-6 years after 1999. A dementia review panel went over every possible case of dementia and cognitive decline found in the entire study. The panel was able to determine if a participant had dementia, and if so, which dementia subtype as well as a date of onset.

            Over the 30 year duration of the study, certain trends were observed. Vascular risk factors had a lower prevalence over time, with diabetes and obesity being the only exceptions and had actually increased over time. Additionally, a trend was observed towards a higher education level over time.

            Ultimately, the study yielded 371 total cases of dementia. A trend was found that mean age at diagnosis had increased over time from 80 to 85 years of age. The total participants and 30 years of data were separated into 4 different periods, referenced as epochs. From the first epoch to the second, the incidence of dementia was down by 22%. Between the first epoch and the fourth, the dementia incidence rate declined by 44%.  Since 1977, an average 20% decline per decade was observed. Alternatively, the incidence decline of Alzheimer’s disease was not significant and did not follow a similar trend, indicating that this decline in incidence over time was not apparent for all diseases and was particular of dementia. The Framingham Heart Study was able to show a decline dementia over 30 years. This trend was also paralleled by an improved cardiovascular heart trend, as well as education level, possibly indicating these factors might have helped progressively decline the occurrence of dementia.

Lena Chatterjee is the 2015-2016 Research Highlights Editor.

10.1056/NEJMoa1504327