Tracing the temporal trends of modifiable risk factors in dementia: insights from the English Longitudinal Study of Ageing (2004–2019)

BackgroundDementia's growing impact, especially in ageing societies such as the UK, emphasises the importance of modifiable risk factors as primary prevention targets. Despite this, the temporal progression and the population attributable fraction (PAF) of dementia attributable to these factors remain unclear. This investigation aims to examine the temporal trajectories of the modifiable risk factors for dementia in England from 2004 to 2019.MethodsWe used data from the English Longitudinal Study of Ageing collected between June, 2004, and July, 2019, covering 76 904 participants. We calculated the PAFs for 12 modifiable risk factors, as recommended by the Lancet Commission on dementia prevention, intervention, and care, and the individual weighted PAFs (IW-PAFs) for each risk factor. We analysed temporal trends to understand the changes in the overall PAF and IW-PAF over the study period.FindingsThe overall PAF for dementia showed a decrease from 46·31% in 2004–05 to 43·95% in 2018–19, but this trend was not significant (p=0·226). Hypertension, with an average IW-PAF of 8·67%, has been the primary modifiable determinant of dementia, trailed by obesity (6·42%), social isolation (5·84%), hearing loss (5·02%), depression (4·89%), low education (4·80%), physical inactivity (3·40%), diabetes (2·61%), smoking (2·08%), excessive alcohol consumption (1·22%), air pollution (0·44%), and traumatic brain injury (0·28%). During 2004–19, only IW-PAFs of low education (p=0·001), social isolation (p=0·034), and smoking (p=0·007) showed significant decreasing trends, whereas IW-PAFs of other factors had either stagnated with insignificant changes or, worryingly, climbed upwards.InterpretationThis investigation provides valuable insights into the temporal trends of modifiable risk factors for dementia in England. The observed trends underscore the continuing relevance of these risk factors and the need for targeted public health strategies to address them. Notable, PAF was based on a theoretical scenario in which dementia risk can be wholly eliminated by removing risk factors, which should be explained with caution in practice.FundingUK Foreign, Commonwealth and Development Office; National Institute for Health and Care Research (NIHR).