Historical development and current status of longitudinal studies of ageing with dementia relevance in the majority world

Longitudinal studies play a crucial role in understanding the progression of ageing-related conditions and dementia, as they offer valuable insights into the incidence, prevalence, risk factors, and associated outcomes. By tracking individuals over an extended period, researchers can observe changes in cognitive function, identify early markers of dementia, and assess the effectiveness of various interventions aimed at slowing the progression of disease symptoms. However, well-designed longitudinal epidemiological research is lacking in low- and middle-income countries (LMICs), where two of every three people living with dementia reside. Dementia is under-recognised, underdiagnosed, undertreated, and under-managed in LMICs, partly due to the high prevalence of stigma and poor health literacy regarding the disease, as well as under-resourced public health systems and limited expertise in mental health. This chapter evaluates the historical development and the current state of longitudinal ageing studies in the majority world, shedding light on their relevance to understanding dementia in the context of LMICs.