Dementia decline heralds hope of reduced burden

By Lucy Piper, Senior medwireNews Reporter

Analysis of participants in the Framingham Heart Study has shown a decline in dementia over a period of 3 decades.

The surveillance data collected indicate that since 1977 there has been, on average, a 20% decline in the incidence of dementia per decade, despite increases in life expectancy, and a 5-year delay in its onset from an average of 80 years to 85 years.

Researcher Sudha Seshadri (Boston University School of Medicine, Massachusetts, USA) and colleagues believe their study “offers cautious hope that some cases of dementia might be preventable or at least delayed.”

They recognise that the worldwide burden of dementia will still continue to increase rapidly as the average life expectancy and the number of people at risk increases, but the team suggests that “primary and secondary prevention might be key to diminishing the magnitude of this expected increase.”

Data were collected for 5205 individuals over 40,192 person–years of follow-up. Across four epochs, the percentage of baseline participants remained at 75% to 78% and more than 2000 participants contributed data in each epoch. There were 371 cases of dementia, based on DSM-IV criteria.

Hazard rates for dementia, adjusted for gender and age, declined steadily, from 3.6 per 100 persons in the first epoch (late 1970s to early 1980s) to 2.8 per 100 persons during the second epoch (late 1980s to early 1990s), 2.2 per 100 persons during the third epoch (late 1990s to early 2000s) and 2.0 per 100 persons during the fourth epoch (late 2000s to early 2010s).

Relative to the first epoch, the incidence of dementia declined by 22% during the second epoch, by 38% during the third epoch and by 44% during the fourth epoch, the researchers report in TheNew England Journal of Medicine.

They note, however, that this decline in dementia was limited to people who had a high school diploma and was consistent with parallel improvements in cardiovascular health also only being seen among individuals with a high school education.

Most indicators of cardiovascular health improved over the course of the study, with the exception of an increased prevalence ofobesity and diabetes, and the incidence of stroke and other cardiovascular diseases decreased.

However, the specific effects of these improvements on dementia risk did not change dramatically over the 3 decades. The researchers did observe an increased benefit of antihypertensive medications in more recent epochs, suggesting improved treatment of stroke and heart disease contributed to the dementia decline, but they emphasise that additional explanations still need to be determined.

In a related editorial, David Jones (Harvard Medical School, Boston, Massachusetts, USA) and Jeremy Greene (Johns Hopkins University School of Medicine, Baltimore, Maryland, USA) say the findings give justification for optimism.

“Evidence of dementia’s decline shows once again that our burden of disease is malleable”, they write, but they warn against becoming complacent, noting that the “burden of disease, ever malleable, can easily relapse.”

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