The chapter presents recent evidence for factors that contribute to aging-related cognitive declines, including both normal and pathological changes. The focus is on non-modifiable and modifiable risk and protective factors and their independent, multi-modal, and interactive effects on trajectories of cognitive change. Findings from long-term longitudinal studies and broad-based epidemiological investigations, as well as short-term experimental and intervention studies are considered. Moderating factors are reviewed in the context of alternative processes and outcomes, such as cognitive reserve, resilience and exceptionality. The chapter concludes with a discussion of goals to reduce or delay neurodegenerative risk and associated cognitive declines and ultimately to prevent the onset of cognitive impairment and dementia.

Recent empirical evidence has documented that US middle-aged adults today are reporting lower mental and physical health than same-aged peers several decades ago. Individuals who attained fewer years of education have been most vulnerable to these historical changes. One overarching question is whether this phenomenon is confined to the US or whether it is transpiring across other high-income and upper-middle-income nations. To examine this question, we use nationally representative longitudinal panel data from five nations across different continents and cultural backgrounds (US, Australia, Germany, South Korea, and Mexico). Results revealed historical improvements in physical health for people in their 40s and early 50s across all five nations. Conversely, the direction of historical change in mental health vastly differed across nations. Later-born cohorts of US middle-aged adults exhibit worsening mental health and cognition. Australian middle-aged adults also experienced worsening mental health with historical time. In contrast, historical improvements for mental health were observed in Germany, South Korea, and Mexico. For US middle-aged adults, the protective effect of education diminished in later-born cohorts. Consistent across the other nations, individuals with fewer years of education were most vulnerable to historical declines or benefitted the least fromhistorical improvements. We discuss potential reasons underlying similarities and differences between the US and other nations in these historical trends and consider the role of education.