A whole-population approach is required for dementia risk reduction

There are estimated to be more than 55 million cases of dementia globally, an increasing majority of which are in low-income and middle-income countries.1WHOGlobal status report on the public health response to dementia.https://www.who.int/publications/i/item/9789240033245Date: Sept 1, 2021Date accessed: December 13, 2021Google Scholar Dementia is characterised by progressive cognitive impairment, affecting a person's daily life beyond what would normally be expected from biological ageing. Dementia is therefore intrinsically linked to the sociocultural and temporal context of what ageing means to a population. In addition to devastation at the individual level, at a population level dementia is a leading cause of morbidity, health and social care costs, and mortality. The absence of effective treatments for dementia means that risk reduction is one of the key public health challenges of our time. The causes of dementia are multiple, complex, and overlapping. Intensive data collection and synthesis efforts over recent years have identified modifiable risk factors for dementia and shown that action on these risk factors has the potential to prevent a substantial proportion of cases, particularly in low-income settings.2Livingston G Huntley J Sommerlad A et al.Dementia prevention, intervention, and care: 2020 report of the Lancet Commission.Lancet. 2020; 396: 413-446Summary Full Text Full Text PDF PubMed Scopus (1261) Google Scholar This important work has led to the development of clinical trials of dementia risk reduction targeting individual behavioural change. Although many trials that are currently underway have yet to publish their results, those that have been published have reported mixed results.3Ngandu T Lehtisalo J Solomon A et al.A 2 year multidomain intervention of diet, exercise, cognitive training, and vascular risk monitoring versus control to prevent cognitive decline in at-risk elderly people (FINGER): a randomised controlled trial.Lancet. 2015; 385: 2255-2263Summary Full Text Full Text PDF PubMed Scopus (1477) Google Scholar, 4Andrieu S Guyonnet S Coley N et al.Effect of long-term omega 3 polyunsaturated fatty acid supplementation with or without multidomain intervention on cognitive function in elderly adults with memory complaints (MAPT): a randomised, placebo-controlled trial.Lancet Neurol. 2017; 16: 377-389Summary Full Text Full Text PDF PubMed Scopus (369) Google Scholar, 5van Charante EPM Richard E Eurelings LS et al.Effectiveness of a 6-year multidomain vascular care intervention to prevent dementia (preDIVA): a cluster-randomised controlled trial.Lancet. 2016; 388: 797-805Summary Full Text Full Text PDF PubMed Scopus (288) Google Scholar Geoffrey Rose's prevention paradox6Rose GA Khaw K-T Marmot M Rose's strategy of preventive medicine: the complete original text. Oxford University Press, New York, NY, USA2008Crossref Scopus (178) Google Scholar describes two broad approaches to prevention. The at-risk individual approach to prevention constitutes targeted interventions to identify individuals at high risk of disease. Individuals identified as being at high risk can then be educated about their risk and supported to take steps to reduce it. The whole-population-based approach to prevention involves interventions that aim to reduce everyone's risk across society. These interventions tend to induce unconscious behavioural change because the most convenient course of action is now a healthier one. The current trials use the at-risk individual approach. These trials have enrolled late midlife and older individuals at risk of developing dementia, with interventions designed to intensively control risk factors such as cardiovascular or cardiometabolic disease, to increase physical activity and healthy dietary patterns, and to address low cognitive stimulation. Such trials are helpful in providing empirical, interventional evidence of dementia's preventability. Additionally, the high prevalence of these risk factors in modern societies mean that a substantial proportion of the target population are eligible to participate. However, an exclusive focus on such approaches, which neglects whole-population-based approaches, will be insufficient to substantially reduce dementia incidence at the population level. We need whole-population-based approaches for three reasons. First, dementia and its modifiable risk factors are highly prevalent. To substantially reduce the absolute burden of disease, we require scalable interventions that efficiently apply available resources to very large numbers of people. Second, dementia occurs as a result of cumulative exposure to multiple risk factors across the life course. Whole-population-based approaches affect the contexts and environments in which people live, work, and play. Thus, they have the potential to reduce the whole risk profile in the whole population across the life course. Third, dementia incidence follows a socioeconomic gradient,7Kivimäki M Batty GD Pentti J et al.Association between socioeconomic status and the development of mental and physical health conditions in adulthood: a multi-cohort study.Lancet Public Health. 2020; 5: e140-e149Summary Full Text Full Text PDF PubMed Scopus (130) Google Scholar and interventions should therefore aim to reduce inequalities. Whole-population-based approaches offer three key advantages here. The first advantage is that they generally require passive engagement and can be designed to be most applicable to individuals from deprived backgrounds. This approach avoids healthy volunteer bias, in which individuals most likely to engage when active enrolment is required are more affluent. Another advantage is that they do not necessitate identification of individuals at high risk of disease, which requires data that are less likely to be available in resource-constrained contexts. The third advantage is that they tend to drive unconscious behavioural change. Unconscious behavioural change (eg, finding yourself exercising more because of the provision of high-quality green spaces in your previously under-served community) is less reliant on cognitive, social, and material resources than interventions that target conscious behavioural change (eg, choosing to go to an exercise class). The resources required for conscious behavioural change are not evenly distributed within our global societies, meaning that approaches reliant on these resources will widen health inequalities.8Marteau TM Rutter H Marmot M Changing behaviour: an essential component of tackling health inequalities.BMJ. 2021; 372: n332Crossref PubMed Scopus (21) Google Scholar The current policy focus, favouring individual-level approaches, will increase inequalities (both within and between countries) and have a relatively small effect on the absolute incidence of disease. A key question, therefore, is what should balanced (both individual-level and population-level approaches) dementia risk reduction look like? The figure considers how policies addressing some modifiable risk factors for dementia might differ according to these two approaches. Both approaches are necessary but insufficient separately. Notably, the examples of whole-population-based approaches require engagement from a much broader range of stakeholders, including national and local governments, industry, the education sector, town planners, and workplaces. Whole-population-based approaches are therefore often seen as political compared with the relatively biomedical individual-level approaches. It is also important to see this work in the context of the broader non-communicable disease agenda, as many of the risk factors listed in the figure are also risk factors for other prevalent diseases such as type 2 diabetes, ischaemic heart disease, and stroke—although other risk factors are relatively exclusive to dementia. Given the association of dementia and its risk factors with low socioeconomic status, it is important to note that adopting whole-population-based approaches does not mean an absence of targeting. Michael Marmot's “proportionate universalism” calls for whole-population approaches, but with a scale and an intensity that are proportionate to the level of disadvantage.9Marmot M Bell R Fair society, healthy lives.Public Health. 2012; 126: S4-10Crossref PubMed Scopus (381) Google Scholar For example, a local government might decide to increase active commuting by investing in, and maintaining, high-quality off-road cycle paths from the suburbs to the city centre, and subsidising cycling equipment. But it might weight this funding on the basis of socioeconomic deprivation, such that the greatest investment goes into the poorest neighbourhoods, where physical activity levels are likely to be lowest. A national government might wish to increase the levels of formal education received for all citizens by introducing a minimum number of years of schooling. Recognising that poorer families rely on the income of teenage children entering the workforce, financial support would be provided to families below an income threshold. The International Research Network on Dementia Prevention (IRNDP), established in 2017, has a goal to “link researchers globally to foster new research and accelerate knowledge translation that will delay or prevent dementia worldwide”. So far, expert IRNDP research groups have led on observational research to identify risk factors, evidence synthesis, and individual-based clinical trials. Now we establish a new expert IRNDP research group: Population-based Approaches to Dementia Risk Reduction. Recognising the increasing burden of dementia in low-income and middle-income countries, and the association of dementia and its risk factors with socioeconomic status in high-income countries, explicit focus will be on research relevant to resource-constrained contexts. This research group aims to balance the global approach to dementia risk reduction, without which we cannot hope to reduce the absolute burden of dementia for future generations. We declare no competing interests. Ethics, evidence, and the environment in dementia risk reduction – Authors' replyTimothy Daly's response to our Comment1 introduces three important considerations that we welcome. Full-Text PDF Open AccessEthics, evidence, and the environment in dementia risk reductionThe Comment by Sebastian Walsh and colleagues on dementia risk reduction for The Lancet Healthy Longevity makes a convincing case for a shift away from individualistic lifestyle interventions to a whole-population approach, which considers both conscious behavioural changes and structural policy changes within society.1 Although the authors provide concrete pragmatic measures at both of these levels, there are three considerations worthy of further reflection on the way to a risk-reducing society. 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