Cognitive and social activities and long-term dementia risk
Authors: Robert P Friedland
Journal: The Lancet Public Health (2021)

I read Sarah Floud and colleagues’ Article on activities and dementia risk with concern.1Floud S Balkwill A Sweetland S Brown A et al.Cognitive and social activities and long-term dementia risk: the prospective UK Million Women Study.Lancet Public Health. 2021; 6: e116-e123Summary Full Text Full Text PDF Scopus (6) Google Scholar Considerable evidence supports the concept that cognitive and physical activities have a beneficial effect on the brain and that they protect against dementia development. Floud and colleagues reported that participation in activities in the 10 years before dementia onset was protective because of reverse causality. Why could this relationship not be due to direct causation? There is considerable biological evidence to support this interaction. While Floud and colleagues’ study had a large sample size of 851 307 women and mean follow-up of 16 years, my view is supported by studies with rigorous disease assessment, as well as a longer study period.2Borenstein A Mortimer J Alzheimer's disease. Life course perspectives on risk reduction. Academic Press, Cambridge, MA2016Google Scholar In a case-control study including people with Alzheimer's disease and controls, aged approximately 72 years, participants were asked about their engagement with 26 activities from ages 20 to 60 years. It was found that the odds ratio for Alzheimer's in those performing less than the mean value of activities was 3·85 (95% CI 2·65–5·5; p<0·001).3Friedland RP Fritsch T Smyth KA et al.Patients with Alzheimer's disease have reduced activities in midlife compared with healthy control-group members.Proc Natl Acad Sci USA. 2001; 98: 3440-3445Crossref PubMed Scopus (348) Google Scholar Furthermore, the Nun Study of Aging and Alzheimer's Disease found that linguistic ability, derived from autobiographies written at a mean age of 22 years, was protective.4Riley KP Snowdon DA Desrosiers MF Markesbery WR Early life linguistic ability, late life cognitive function, and neuropathology: findings from the Nun Study.Neurobiol Aging. 2005; 26: 341-347Crossref PubMed Scopus (187) Google Scholar, 5Snowdon DA Kemper SJ Mortimer JA et al.Linguistic ability in early life and cognitive function and Alzheimer's disease in late life: findings from the Nun Study.JAMA. 1996; 275: 528-532Crossref PubMed Google Scholar Also, Floud and colleagues’ study did not assess intensity of participation in the activities assessed, unlike the case-control and Nun studies. Floud and colleagues recommend that guidelines concerning recommendations for activities to prevent dementia, “…should be reconsidered”. This is unwise, considering the available evidence for direct causation, as well as the many studies showing that such activities are nonetheless valuable in the prevention of heart disease and hypertension. I declare no competing interests. Cognitive and social activities and long-term dementia risk: the prospective UK Million Women StudyLife has to be lived forwards, but can be understood only backwards. Long before dementia is diagnosed, there is a progressive reduction in various mental and physical activities, but this is chiefly because its gradual onset causes inactivity and not because inactivity causes dementia. Full-Text PDF Open AccessCognitive and social activities and long-term dementia risk – Authors' replyThe pathological processes that culminate in dementia tend to be gradual, with preclinical manifestations developing slowly over some years. Consistent with this slow progression, weight loss and reductions in physical activity can be seen at least a decade before any definite record of dementia.1,2 In prospective studies, reverse causation bias (whereby preclinical dementia causes behavioural and other changes) would be greater during the first decade after activities were recorded, particularly during the first 5 years, than during the second decade of follow-up. Full-Text PDF Open Access