Combined healthy lifestyle behaviours and incident dementia: A systematic review and dose-response meta-analysis of cohort studies

Background: The associations of combined healthy lifestyle behaviours and incident dementia have not been systematically reviewed and the dose-response relationship was uncertain. Objectives: To evaluate the associations of combined healthy lifestyle behaviours with incident dementia and other cognitive outcomes, assess the dose-response relationship between the number of lifestyle behaviours and incident dementia, and summarise the adherence to healthy lifestyle behaviours. Design: Systematic review and meta-analysis. Methods: PubMed, EMBASE, Web of Science and PsycINFO were searched from inception to 20 Jan 2024. Cohort studies reporting associations of combined healthy lifestyle behaviours with incident dementia or other cognitive outcomes were included. We used the random-effects meta-analysis to pool the risk estimates and the robust error meta-regression method to examine the dose-response relationship. The methodological quality was assessed using the Newcastle-Ottawa Scale. Results: A total of 22 articles including 25 cohort studies mostly from high-income economics were included, with all assessed as high methodological quality. Adherence to a healthy lifestyle was associated with a decreased risk of incident dementia, either per healthy lifestyle behaviour increase (pooled hazard ratio 0.89, 95 % confidence interval 0.85-0.94) or the highest level versus the lowest level (pooled hazard ratio 0.61, 95 % confidence interval 0.49-0.76). An inverse, linear dose-response relationship (Pnon-linear = 0.845) between the number of healthy lifestyle behaviours and incident dementia was observed, with an 11 % risk reduction for each healthy behaviour increase. A relatively limited number of included studies indicated that adherence to a healthy lifestyle combination could yield benefits for cognitive decline, global cognition, memory and executive function. In addition, the adherence rates typically decreased as the number of healthy lifestyle behaviours increased. Conclusions: Adherence to a healthy lifestyle was associated with a lower risk of incident dementia and other cognitive outcomes. It is important to find a subtle balance between the benefits and adherence. Further large cohort studies for combined lifestyle behaviours with specific cognitive outcomes and dose-response relationships are required, especially based on middle- and low-income populations. Registration: The study was registered in PROSPERO (CRD42023418509). Tweetable abstract: Engaging in a greater number of healthy lifestyle behaviours yields increased benefits in preventing dementia, albeit with lower adherence rates as a trade-off. Finding a delicate balance between the benefits and adherence is crucial.