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Floud S, Balkwill A, Sweetland S, Brown A, Reus EM, Hofman A, Blacker D, Kivimaki M, Green J, Peto R, Reeves GK, Beral V. Cognitive and social activities and long-term dementia risk: the prospective UK Million Women Study. Lancet Public Health. 2021 Feb;6(2):e116-e123. PubMed.
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Sahlgrenska University Hospital
This study by Floud et al. is a very nice and large study including over 800,000 women followed for approximately 16 years. The women were aged approximately 60 years when information on social and cognitive activity was collected. The social and cognitive activities were adult education, engagement in group activities including art, craft, or music, and engaging in voluntary work. They found that the protective effect of social and cognitive activity on risk of dementia was especially strong during the first four years of follow-up and that the effect diminished during the second decade. This has also been shown for physical activity in a recent report based on the same population and with similar methods.
As the authors state, these results show that engagement in leisure-time activity declines due to preclinical dementia. The authors also conclude that leisure-time activity has no causal relation to dementia risk. However, although evidence suggest that engagement in leisure-time activities declines in the years preceding dementia onset, leisure-time activities may still have a causal relation with dementia risk. One need not exclude the other.
This is supported by findings from studies with observation periods over four decades (e.g., Carlson et al., 2008; Najar et al., 2019; Hörder et al., 2018). In our 2019 study, we found that midlife leisure-time cognitive activity reduced risk of all-cause dementia and Alzheimer’s disease after 44 years of follow-up, while midlife physical activity was associated with reduced risk of mixed vascular dementia disorders. Also, to minimize the risk of preclinical dementia affecting our results, we performed sensitivity analyses excluding those with dementia within 22 years of follow-up. The results remained similar, if not a little bit stronger for at least physical activity, which then also associated with all-cause dementia.
There are of course several methodological differences between these two studies that could explain the divergent results. For example, the women included in our study were younger at baseline (mean age 47 years), assessment of dementia differed between the studies (we used the DSM-III-R criteria, which are based on neuropsychiatric examinations, while Floud and colleagues used electronic health records), and we had a longer follow-up period.
In conclusion, this work highlights an important aspect in studies examining risk factors for dementia, namely the risk of reverse causation due to preclinical dementia. Therefore, studies with observation periods longer than the assumed preclinical phase of dementia (>20–30 years) are needed to better understand causal relations between lifestyle factors and risk of dementia.
References:
Carlson MC, Helms MJ, Steffens DC, Burke JR, Potter GG, Plassman BL. Midlife activity predicts risk of dementia in older male twin pairs. Alzheimers Dement. 2008 Sep 1;4(5):324-31. PubMed.
Najar J, Östling S, Gudmundsson P, Sundh V, Johansson L, Kern S, Guo X, Hällström T, Skoog I. Cognitive and physical activity and dementia: A 44-year longitudinal population study of women. Neurology. 2019 Mar 19;92(12):e1322-e1330. Epub 2019 Feb 20 PubMed.
Hörder H, Johansson L, Guo X, Grimby G, Kern S, Östling S, Skoog I. Midlife cardiovascular fitness and dementia: A 44-year longitudinal population study in women. Neurology. 2018 Apr 10;90(15):e1298-e1305. Epub 2018 Mar 14 PubMed.
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