As we all know, people are living longer and obesity is at appalling levels. For both these (completely separate!) reasons, we expect to see growing rates of dementia. A new analysis using data from the long-running Framingham Heart Study offers some hope to individuals, however.
Looking at the rate of dementia during four distinct periods in the late 1970s, late 1980s, 1990s, and 2000s, using data from 5205 older adults (60+), the researchers found that there was a progressive decline in the incidence of dementia at a given age, with an average reduction of 20% per decade since the 1970s (22%, 38%, and 44% during the second, third, and fourth epochs, respectively).
There are two important things to note about this finding:
- the decline occurred only in people with a high school education and above
- the decline was more pronounced with dementia caused by vascular diseases, such as stroke.
The cumulative risk over five years, adjusted for age and gender, were:
- 3.6 per 100 persons during the first period (late 1970s and early 1980s)
- 2.8 per 100 persons during the second period (late 1980s and early 1990s)
- 2.2 per 100 persons during the third period (late 1990s and early 2000s)
- 2.0 per 100 persons during the fourth period (late 2000s and early 2010s).
Part of the reason for the decline is put down to the decrease in vascular risk factors other than obesity and diabetes, and better management of cardiovascular diseases and stroke. But this doesn't completely explain the decrease. I would speculate that other reasons might include:
- increased mental stimulation
- improvements in lifestyle factors such as diet and exercise
- better health care for infectious and inflammatory conditions.
The finding is not completely unexpected. Recent epidemiological studies in the U.S., Canada, England, the Netherlands, Sweden and Denmark have all suggested that “a 75- to 85-year-old has a lower risk of having Alzheimer’s today than 15 or 20 years ago.” Which actually cuts to the heart of the issue: individual risk of dementia has gone down (for those taking care of their brain and body), but because more and more people are living longer, the numbers of people with dementia are increasing.
 . Incidence of Dementia over Three Decades in the Framingham Heart Study. New England Journal of Medicine [Internet]. 2016 ;374(6):523 - 532. Available from: http://dx.doi.org/10.1056/NEJMoa1504327