Abstract
Along with rapid global population aging, the age-related cognitive disorders such as mild cognitive impairment (MCI) and dementia have posed a serious threat to public health, health care system, and sustainable economic and societal development of all countries. In this narrative review, we seek to summarize the major epidemiological studies from the life-course perspective that investigate the influence of genetic susceptibility [e.g., apolipoprotein (APOE) ε4 allele] and intellectual or psychosocial factors (e.g., educational attainments and leisure activities) as well as their interactions on cognitive phenotypes in aging. Numerous population-based studies have suggested that early-life educational attainments and socioeconomic status, midlife work complexity and social engagements, late-life leisure activities (social, physical, and mentally-stimulating activities), certain personality traits (e.g., high neuroticism and low conscientiousness), and depression significantly affect late-life cognitive phenotypes. Furthermore, certain intellectual or psychosocial factors (e.g., leisure activities and depression) may interact with genetic susceptibility (e.g., APOE ε4 allele) to affect the phenotypes of cognitive aging such that risk or beneficial effects of these factors on cognitive function may vary by carrying the susceptibility genes. Current evidence from the randomized controlled trials that support the cognitive benefits of cognitive training among cognitive healthy older adults remains limited. The cognitive reserve hypothesis has been proposed to partly explain the beneficial effects of lifetime intellectual and psychosocial factors on late-life cognitive function. This implies that, from a life-course perspective, preventive intervention strategies targeting multiple modifiable intellectual and psychosocial factors could interfere with clinical expression of cognitive disorders in old age and delay the onset of dementia syndrome, and thus, may help achieve healthy brain aging.
Highlights
Cognitive aging can be referred to as a process of gradual deteriorations in cognitive function that occur as people age
Whereas it has been well-established that dementia and cardiovascular disease share common cardiometabolic risk factors from midlife onward, increasing evidence supports the potential role of the life-course intellectual factors in delaying the onset of cognitive disorders
Since the early 1990s when the Shanghai Aging Study linked illiteracy or low education with late-life sporadic dementia and Alzheimer’s disease (Zhang et al, 1990), numerous epidemiological studies have suggested that early-life low educational attainment is associated with an increased risk of late-life cognitive impairment and dementia, in which the association could not be explained by unhealthy lifestyle and low occupational position associated with low education (Karp et al, 2004; Ngandu et al, 2007; Qiu et al, 2010)
Summary
Cognitive aging can be referred to as a process of gradual deteriorations in cognitive function that occur as people age. Several observational studies that were initiated among young and middle-aged people in the 1960s and the 1970s have shifted their initial focus from metabolic and cardiovascular disease (e.g., obesity, hypertension, diabetes, and ischemic heart disease) to phenotypes of cognitive aging (e.g., MCI and dementia) as the study cohorts age (Irie et al, 2008; Håkansson et al, 2009; Chang et al, 2010) These long-term observational studies have significantly contributed to the better understanding of multifactorial etiology and the process of cognitive aging and dementia from the life-course perspective (Whalley et al, 2006; Fratiglioni and Qiu, 2011; Qiu, 2012). This implies that owing to the relatively long-term latent (pre-clinical) period of dementia, the potential reverse causality should be kept in mind when interpreting the associations between exposures to environmental factors and the risk of dementia even from the prospective cohort studies
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