There is a growing amount of literature exists regarding the benefits of adult education and lifelong learning (See BeLL study, and Schuller, 2017), especially there is strong evidence regarding the positive impact of adult learning on physical health (smoking cessation, amount of exercise, lower risk of coronary heart disease and reduction in drug abuse, see Feinstein & Hammond, 2004; Chandola et al., 2011) and mental wellbeing  (a sense of identity, an ability to cope, a feeling of purpose in life, a greater level of wellbeing, increase in life satisfaction (Duckworth & Cara, 2012; Hammond, 2004). However, the preventive effects of continuing education on cognitive decline and dementia have not been comprehensively and systematically assessed yet. In an aging society, where Dementia is getting a serious health and economic issue it would be crucial to work on alternative preventive programs.

The underlying risks for Alzheimer’s-type dementia are not yet thoroughly understood, and no curative treatment has been found (Scarmeas et al., 2009). Systematic reviews assessing risk factors indicate that low educational level, decreased physical activity, unhealthy diet, smoking, and alcohol abuse might be predictors of dementia [IOM, 2015; Wilson et al. 2013; Bosma et al., 2002; Hultsch et al., 1999). Likewise, chronic medical conditions such as cardiovascular diseases, diabetes, cancers, depression, or genetic factors increase the risk of dementia (IOM, 2015). Some studies, however, found a protective association of cognitively stimulating activities, such as learning a new language in middle age, with a slower cognitive decline during late life (Wilson et al., 2007; Tucker & Stern, 2011; Stern, 2012; Valenzuela & Sachdev, 2006). Such results underpin a theory called the “cognitive reserve hypothesis” (Scarmeas & Stern, 2004). According to this theory, through every activity that stimulates the brain, the cognitive reserve gets boosted and the resistance towards any dementia-related brain pathology gets stronger (Ngandu et al., 2007). A larger cognitive reserve acquired by continuing education activities, thus, might protect against cognitive decline.

For this systematic review, we define continuing education as structured learning activities and programs provided by formal and non-formal educational institutions for persons beyond the age of compulsory schooling. These activities are designed to help individuals satisfy learning needs and interests, to enrich knowledge, to develop and improve abilities and skills, and to foster personality, social competences, families, networks, health, and professional life. Continuing education is voluntary and based on topics and courses that are not directly connected to any special job position or vocational training [UNESCO, 1993; OECD, 1977; Cedefop, 2008; Kil & Thöne-Geyer, 2012).

The multidisciplinary scientific team conducted a systematic review to summarise the evidence investigating the preventive effects of continuing education on the development of cognitive impairment and Alzheimer’s-type dementia using the following questions:

Key question 1a: In adults 45 years of age or older with normal cognition or merely subjective cognitive impairment, does continuing education lead to a reduction in the risk of mild cognitive impairment or Alzheimer’s-type dementia compared with no continuing education?

Key question 1b: (In case no evidence on continuing education is available or the evidence is sparse): In adults 45 years of age or older with normal cognition or merely subjective cognitive impairment, do leisure activities lead to a reduction in the risk of mild cognitive impairment or Alzheimer’s-type dementia compared with no continuing education?

Key question 2: What are the potential harms of continuing education?

Key question 3: Do benefits and harms differ by subgroups based on age, sex/gender, race or ethnicities, level of education, or duration of intervention?

Key question 4: What is the optimal age to start continuing education to prevent mild cognitive impairment or dementia?

To assess evidence directly addressing our objectives, we conducted a systematic review. The protocol of this systematic review was published and registered in PROSPERO (International Prospective Register of Systematic Reviews) (Registration number CRD42017063944). We addressed our research questions with two different methodological approaches: 1) We performed a systematic review of primary studies to assess the preventive effects and potential harms of continuing education provided by formal and non-formal institutions (key questions 1a, 2, 3, and 4) 2) We conducted an overview of systematic reviews to determine the preventive effects and potential harms of related leisure activities (e.g. playing cards, reading books, etc.¸ key question 1b). We chose this two-step approach because studies in the field of continuing education and dementia are very rare. Certain leisure activities, however, are able to mimic continuing education regarding content (e.g. learning a new language privately versus learning a new language as an organized educational activity). Leisure activities are not our primary focus of interest but can be considered as surrogate interventions for continuing education in some circumstances. MEDLINE, PsycINFO, EMBASE, CENTRAL, CINAHL and Scopus for published studies and grey literature databases for unpublished studies from January 1990 to April 2018 were searched systematically. We used a priori established inclusion and exclusion criteria. Two authors independently assessed inclusion and exclusion on abstract and full-text level, rated risk of bias, and determined the certainty of evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation). We resolved all discrepancies by consensus. We synthesized the available evidence narratively. Following criteria was used for eliminating studies during the review process: • Participants: healthy adults (45 years old or older) • Intervention: continuing education activities • Comparators: studies with control groups • Outcomes: cognitive impairment / Alzheimer‘s-type dementia • Timing: 3 months of duration, 1 year of follow up • Settings: continuing education institutions

Our searches identified 4927 studies. For the systematic review, two publications on the same prospective cohort study (Tasmanian Healthy Brain Project) met inclusion criteria; for the overview of reviews we included five systematic reviews. Based on 459 participants, preliminary data of the ongoing cohort study indicated that cognitive reserve statistically significantly increased in persons attending university classes compared to the control group (92.5% vs. 55.7%). Likewise, language processing capacities statistically significantly improved. Episodic memory, working memory, and executive function did not differ significantly between groups. Systematic reviews consistently reported a positive association between participation in cognitively stimulating leisure activities and reduced incidence of dementia and improved cognitive test performance. The five included systematic reviews investigating cognitive leisure activities demonstrated both a reduction of MCI and Alzheimer’s-type dementia incidence and improvements in several cognitive domains. Thus, it is possible to conclude that available results demonstrate that cognitive reserve increases through continuing education and show a positive association of cognitive leisure activities with both improved cognitive function and lower dementia incidence. Healthcare providers and policymakers should promote a healthy lifestyle, which also includes being cognitively active throughout late life supported by lifelong learning through continuing education institutions which offer a wide range of cognitive stimulating activities. Results will be discussed in relation to limitations of the studies and our systematic review.

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