mental and social activities dec dementia

Another dementia study. This one finding that increased cognitive stimulation and social connections and support are associated with reduced risk of dementia (see dementia dec with inc cognit reserve jamaneuro2019 in dropbox, or doi:10.1001/jamaneurol.2019.2455)

Details:
--1602 participants free of initial dementia in the Rush Memory and Aging Project, a community-based cohort study with annual follow-up from 1997-2018
--baseline: 76% women, mean age 80, education 15 yrs, never smokers 57%/ever 40%/current 3%, alcohol 61% never or occasional/28% light-to-moderate/12% heavy, BMI 27, MMSE 29 (out of 30), heart disease 9%/hypertension 68%/cerebrovasc dz 9%/diabetes 15, APOE e4 20%
--mean follow-up 6 years, max 20 years, providing 9722 person-yrs of follow-up
--611 people died and had autopsies during follow-up
--they assessed “cognitive reserve” (CR), measured by the proxy construct of education, and social and cognitive activities:
    --education: years of education based on reported years of school (mean was 15 years)
    --cognitive activities: early-life (6-12yo), midlife (young adulthood, approx 18yo, and middle age, approx. 40yo), and late life cognitive activities, evaluated by 37-item cognitive activity questionnaire at baseline, including such items as reading books, visiting library, writing letters
    --social activity in late life: frequency of such things as going to restaurants, going on day or overnight trips, volunteering/doing unpaid community work, visiting relatives or friends, participating in groups (eg senior centers), attending religious services. Also social network function and size (eg connectedness with family/children/close friends with whom they could talk about private matters)
--clinical diagnosis of dementia and Alzheimer Disease (AD) was per specialty guidelines

Results:
--386 people developed dementia (24%)
    --357 had AD-related dementia (22%), 93% of the total
--compared to patients in the lowest CR tertile, adjusting for age, sex, smoking, alcohol, physical activity, BMI, MMSE score, heart disease, hypertension, cerebrovasc disease, diabetes, APOE e4, and death:
    --those in the middle tertile had 23% decreased risk of dementia, with adjusted HR 0.77 (0.59-0.99)
    --those in the highest tertile had 39% decreased risk of dementia, with adjusted HR 0.61 (0.47-0.81)
--limiting to those with AD, the same decreased risk [not surprising, since the vast majority of those with dementia had AD)
--also, the time to developing dementia varied by CR tertile: 12 years in those in th lowest tertile, 15 yrs in the middle, and >20 years in the top tertile
--in the 611 people getting autopsies (mean age 83), 241 were diagnosed as having incident dementia
    --CR was not associated with most brain pathologies, BUT after additional adjusting for brain pathologies, there was a 40% decreased risk of dementia, HR 0.60 (0.42-0.86), with similar reduction for AD-related dementia
    --the highest CR tertile had a 43% decreased dementia risk, even in those with lots of Alzheimer’s disease pathology at autopsy, HR 0.57 (0.37-0.87), and 66% decrease in those with any gross infarcts, HR 0.34 (0.18-0.62)
--on supplemental analyses: no difference in results when excluding those with mild cognitive impairment at baseline, removing education from the model, removing late-life cognitive and social activities, or by the patients’ sex
   
Commentary:
--this study shows that the group with the most cognitive activity, education and social supports had significantly less dementia (including AD) in a dose-dependent way, and this was true even in those patients who died and had AD or vascular pathologies on autopsy
--other studies have found that patients with lots of AD-related neuropathology by both neuroimaging and pathology studies do not have clinical dementia
    --25% of cognitively healthy adults have increased b-amyloid plaques in the brain
--the CR concept is that increased brain stimulation should increase brain resiliency, perhaps through increased brain network efficiency (eg, stimulating more neuronal connnections). The above noted inconsistent relationship between gross pathologic brain changes and clinical cognitive ability confirm that these pathologic changes are not determinant
    --the Mediterranean diet, however, seems to improve both: improved cognition as well as greater gray and white matter brain volumes (see http://gmodestmedblogs.blogspot.com/2015/11/mediterranean-diet-and-brain-volume.html)
--study limitations include that as a longitudinal cohort study, one cannot establish causality (eg, unknown confounders, perhaps related to living conditions, differences in diet/exercise not covered in their analysis, SES, etc). also, for unclear reasons, the vast majority (93%) had AD (very few with vascular dementia, for example).

So, this study adds to prior studies finding that more cognitive and social connections are associated with less dementia, and that if dementia happens, it tends to happen later in life. It is notable in this study that even when there is strong pathological evidence of Alzhemier’s, there is less likelihood of clinical dementia in those with more extensive cognitive/social/educational lives. And this study adds to many suggesting that healthier lifestyles also decrease the likelihood of clinical dementia, including the review reported recently: see http://gmodestmedblogs.blogspot.com/2019/07/dementia-genetics-and-lifestyle-both.html (which also includes references to other blogs)

geoff​

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