As the incidence of dementia is rapidly increasing around the world, especially in developing countries, it has become one of the most important health and social challenges facing humanity. This volume has reviewed research on social and psychological factors that could moderate the development of dementia in late life through social connection. This last chapter reviews psychosocial interventions connected with various aspects of social connection or lack thereof, such as social networks, social relationships, social engagement, loneliness, and sense of belonging, to examine interventions and their key factors that have shown efficacy in enhancing the moderators. It also introduces three evidence-based components that can be adopted in strategies and policies that aim to reduce the modifiable risks of dementia.

Sources of resilience against neurodegenerative diseases, such as cognitive reserve, have been identified as modifiable factors that can prevent the manifestation of clinical dementia. A recent trend in dementia research has employed the concepts of reserve and resilience in the context of a lifespan to develop a life course approach, which integrates the risks of dementia and provides prevention strategies throughout life. This chapter introduces the life course approach to understanding dementia, which is a scientific discipline based on the span of life involving biology, psychology, and the social sciences in a single integrated causal structure to provide a framework to organize the multifactorial process involved in human aging and dementia. The cognitive reserve hypothesis and essential studies validating the theory are introduced; these report the moderating effects of literacy and formal education in dementia manifestation. Brain maintenance, another important component in understanding the resistance to brain aging and neurodegenerative diseases, is also discussed. Lastly, the chapter proposes a hypothetical pathway model to help understand the complex interaction between social relation and brain aging underlying the moderation that could either reduce or increase the risks of dementia.

Loneliness is a complex trait that has been linked to negative mental and physical health outcomes, including cognitive impairment. With mounting efforts to examine the underlying mechanisms of the link between loneliness and health, recent genomics studies suggest genetic predispositions associated with social isolation and cognitive functions. Ongoing genome-wide association studies (GWASs) have identified several genetic loci linked to age-related neuropathological conditions, including the apolipoprotein E (APOE e4) allele. Moreover, emerging evidence suggests genetic influences on loneliness and social integration. In addition to the genetic factors, social genomic research suggests altered gene expression patterns under social isolation or neurodegenerative diseases; for example, chronic loneliness triggers less effective immune response gene expression patterns (conserved transcriptional response to adversity [CTRA]) in white blood cells. Moreover, a recent transcriptional analysis reported altered gene expression patterns associated with myelination in the prefrontal cortex of patients with Alzheimer’s disease. These genomics studies not only suggest that loneliness and neuropathological processes are polymorphic heritable traits but also that genetic variants interact with environmental factors regulating gene expressions on the transcriptional level. This chapter focuses on social genomics research that investigates the favorable social conditions (e.g., social integration) linked to altering gene expression profiles.

A growing body of evidence suggests a strong link between how individuals maintain an enriched social network and their brain health. Both the quantity and quality of social networks provide abundant social connections. Through persistent social interactions, individuals’ neurocognitive health appears to benefit from cognitively stimulating activity as well as social support. By utilizing various neuroimaging methods, researchers have found that maintaining an enriched social network is likely to lead to better neural functioning that could delay or counter the effects of neuropathological progression in late life. This chapter reviews studies examining the relationship between social network characteristics and neurocognitive health. The studies highlight that social connectedness and brain functioning have reciprocal effects. It also discusses whether larger and cohesively connected social networks lead to a healthier brain and better cognitive function, as well as the moderators of this association.