Just in time for the big AAIC2019 meeting, three recent articles may provide better evidence that increased activity (i.e. exercise or mental work or lifestyle) may have an impact on dementia incidence or severity, even in the face of neuroimaging or brain autopsy evidence of an amyloid-beta burden, or genetic risk, in subjects.

These are basically correlation studies with retrospective components, not direct clinical intervention studies.

The first is from the Harvard Aging Cohort in JAMA Neurology; in previous studies, these subjects actually improved on their cognitive tests over time, suggesting they learn well (no comment). Rabin et al had a group of 182 subjects, initially clinically normal, who had PET scans for amyloid and MRI scans for sizing areas of the brain. Subjects wore pedometers.  Adjusting and controlling for vascular risk factors, those who walked more did better, even if they had higher amyloid-beta on PET scan (seemingly different than Mayo studies which call amyloid on PET either positive or negative).  Subjects’ hippocampal volumes still seemed to shrink even in those who walked more, but other brain areas seemed better preserved.  Figure 1B also shows that some subjects improved on their cognitive scores, so refreshing to see in these longitudinal studies with seemingly inevitable declines!

The second is from a Rush (Chicago) cohort in JAMA Neurology, looking at the concept of “cognitive reserve” and correlating brain pathology at autopsy.  Cognitive Reserve (CR) is variously defined but assessed here based on factors such as education, lifespan cognitive activities, and social activities/network.  There is a hypothesis that stronger reserve leads to less overt dementia; Hu et al had a group of 1602 subjects followed over time for CR; 611 had eventual brain autopsies.  Higher CR scores seemed to be associated with less dementia, even when there was an amyloid-beta burden in the brain.

The third article is from a NHS-UK cohort, in JAMA;  Lourida et al studied almost 200-thousand folks with genetic testing information (amyloid-associated and other dementia risk genes) and correlated their lifestyle (smoking, alcohol, diet and activity, over 1.5 million person-years), with an ICD-coded diagnosis of dementia. Even with high genetic risks scores and an unfavourable lifestyle (ooooh, it that judgy?) the incidence of dementia was less that 2%. But those with higher genetic risk and a better lifestyle seemed to have about one-third fewer cases of dementia than those with high risk and a bad lifestyle.

So, is amyloid-beta all that important, or can you walk it away, or take more classes, or do more sudoku, and go to more fun active parties (but not at smoking pubs)?

Earlier this year, I was “mad and sad” at the World Health Org’s Dementia Risk Reduction document, because their own evidence tables show that many of the articles they studied were of moderate to low certainty; they obviously worked hard at meta-analyses (review of reviews), but I wasn’t so sure about their making vague recommendations based on uncertain data.

While I still have mixed feelings about the WHO guidelines, perhaps the WHO authors had heard some of this presented at meetings, and couldn’t cite the then unpublished work.  These articles are not total convincers (all three have nice “limitations” sections), but they help me, at least, feel less guilty about going out and having fun.

This blog is not so much about prevention.  Many folks with Early-Onset (Young-Onset) Alzheimer Disease don’t seem to have ANY of the twelve WHO risk factors, had a good lifestyle, and would seem to ace cognitive reserve, so prevention strategies based on these ideas would probably not help them.  Work that may help prevention is important, but how do we help those already afflicted, especially if amyloid is not crucial?