Neuropsychologia 45 (2007) 459–464 Note Bilingualism as a protection against the onset of symptoms of dementia Ellen Bialystok a,b,∗ , Fergus I.M. Craik b,c , Morris Freedman b,d,e a Department of Psychology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3 b Rotman Research Institute at Baycrest, Canada c Department of Psychology, University of Toronto, Canada d Division of Neurology, Baycrest, Canada e Department of Medicine, Division of Neurology, Mt. Sinai Hospital, University Health Network, and University of Toronto, Canada Received 19 June 2006; received in revised form 23 October 2006; accepted 24 October 2006 Abstract This study examined the effect of lifelong bilingualism on maintaining cognitive functioning and delaying the onset of symptoms of dementia in old age. The sample was selected from the records of 228 patients referred to a Memory Clinic with cognitive complaints. The final sample consisted of 184 patients diagnosed with dementia, 51% of whom were bilingual. The bilinguals showed symptoms of dementia 4 years later than monolinguals, all other measures being equivalent. Additionally, the rate of decline in Mini-Mental State Examination (MMSE) scores over the 4 years subsequent to the diagnosis was the same for a subset of patients in the two groups, suggesting a shift in onset age with no change in rate of progression. © 2006 Elsevier Ltd. All rights reserved. Keywords: Bilingualism; Cognitive reserve; Dementia Factors that may delay onset of dementia are of great impor- tance given the social and economic burden of this disorder. According to Brookmeyer, Gray and Kawas (1998), a 2-year delay in onset of Alzheimer’s disease (AD) would reduce the prevalence in the United States by 1.94 million after 50 years, and delays as short as 6 months could have substantial public health implications. Many of the factors predisposing a person to dementia are biological (Corder et al., 1993), so the search for methods to delay onset has focused largely on pharmacological and other biologically-based therapies. There is growing evi- dence, however, that some environmental factors can maintain cognitive functioning in older adults and mitigate the effects of illnesses that produce dementia. Notably, research on “cognitive reserve” has demonstrated that lifestyle factors, such as physical activity, stimulating leisure involvement, and social engagement play a role in postponing the onset of AD and other demen- tias (Alexander et al., 1997; Scarmeas, Levy, Tang, Manly, & Stern, 2001; Scarmeas & Stern, 2003; Singh-Manoux et al., 2003; Stern, 2002). The literature on brain reserve is somewhat contentious, but several recent large-scale reviews have provided a context for ∗ Corresponding author. Tel.: +1 416 736 5115x66109; fax: +1 416 736 5814. E-mail address: ellenb@yorku.ca (E. Bialystok). conflicting results. The overall notion is that some factors allow a person to function within a normal cognitive range, despite the presence of brain pathology that would usually be associ- ated with dementia. For example, Mortimer (1997) found that between 10 and 40% of autopsy cases showing brain pathology exceeding the criteria for AD had shown no signs of cognitive impairment before death. Similarly a population-based study carried out by the UK Medical Research Council (quoted by Valenzuela & Sachdev, 2006a) found that more than 30% of individuals with mild and severe AD pathology at autopsy had shown no previous signs of cognitive impairment. Valenzuela and Sachdev (2006a) distinguish between, ‘neurological brain reserve’ and ‘behavioral brain reserve.’ Proponents of neurologi- cal brain reserve argue that peak brain volume can ameliorate the effects of brain pathology on cognitive performance and signs of dementia. This type of brain reserve is thus presumably biologi- cal and possibly genetic in origin. On the other hand, behavioral brain reserve (also referred to as cognitive reserve, the term used in the present report) suggests that sustained complex mental activity protects against dementia in terms of both incidence (Valenzuela & Sachdev, 2006a) and the rate of cognitive decline in elderly individuals (Valenzuela & Sachdev, 2006b). In their review of behavioral brain reserve, Valenzuela and Sachdev (2006a) found strong evidence for protection against 0028-3932/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2006.10.009