Much of the scientic literature in this area uses a phrase like ‘dementia prevention’ to refer to reducing the prevalence of dementia in a specic population. However, more recently some concerns have been expressed about this use of language, which highlights a frequent confusion between
a description at the level of the population and one at the level of the individual. In his classic paper ‘Sick individuals and sick populations’, Georey Rose distinguishes between factors which aect the incidence of a disease in a population and those which aect whether an individual will develop the disease (Rose, 1985). For example, if a public health intervention succeeds in reducing a risk factor in the population (such as shiing the population distribution of systolic blood pressure to the le – i.e. more like the Kenyan nomads than the London civil servants in Figure 55.1) this may reduce the incidence of dementia. However, even in the lower risk population as a whole, there will still be individuals with ‘high’ levels of the risk factor and, thus, still at increased risk. Indeed, an individual with an optimized risk factor prole may still develop dementia, assuming that this single risk factor is not, on its own, a sucient cause. Alternatively, the individual may unsuccessfully attempt to reduce this risk factor, even though the population mean of the risk factor and the incidence of dementia both reduce. e individual in this case might meet talk of ‘prevention’ with consternation – they reduced their level of the risk factor but still developed dementia; or they tried and failed to diminish the risk factor, thus failing to prevent dementia. Does this mean they are in some way responsible for developing the disease? It is clear that we must be very careful, both in our thinking and our language here. Indeed, some have called for us to talk in terms of ‘risk reduction’ rather than ‘prevention.’ However, there is a clear and important dierence between these concepts – risk reduction strategies would focus on the exposure variable thought to be associated with the outcome, whereas prevention implies a focus on reducing the frequency or incidence of the outcome, which may be achieved not only by risk reduction but also specic – perhaps pharmacological – interventions. ‘Risk’ in the former sense could potentially be reduced but is unlikely to be eliminated completely. Notwithstanding these caveats,
for simplicity we will continue to use the term ‘prevention’ in this chapter.