title: Bilingualism delays age at onset of dementia, independent of education and immigration status.
abstract: OBJECTIVE
  The purpose of the study was to determine the association between bilingualism and age at onset of dementia and its subtypes, taking into account potential confounding factors.
  
  
  METHODS
  Case records of 648 patients with dementia (391 of them bilingual) diagnosed in a specialist clinic were reviewed. The age at onset of first symptoms was compared between monolingual and bilingual groups. The influence of number of languages spoken, education, occupation, and other potentially interacting variables was examined.
  
  
  RESULTS
  Overall, bilingual patients developed dementia 4.5 years later than the monolingual ones. A significant difference in age at onset was found across Alzheimer disease dementia as well as frontotemporal dementia and vascular dementia, and was also observed in illiterate patients. There was no additional benefit to speaking more than 2 languages. The bilingual effect on age at dementia onset was shown independently of other potential confounding factors such as education, sex, occupation, and urban vs rural dwelling of subjects.
  
  
  CONCLUSIONS
  This is the largest study so far documenting a delayed onset of dementia in bilingual patients and the first one to show it separately in different dementia subtypes. It is the first study reporting a bilingual advantage in those who are illiterate, suggesting that education is not a sufficient explanation for the observed difference. The findings are interpreted in the context of the bilingual advantages in attention and executive functions.
authors.affiliation: From the Department of Neurology (S.A., M.S., A.K.S., S.K.), Nizam's Institute of Medical Sciences, Hyderabad, India; Department of Psychology (T.H.B.), Centre for Cognitive Aging and Cognitive Epidemiology and Centre for Clinical Brain Sciences, University of Edinburgh, UK; Department of Linguistics (V.D.), Osmania University, Hyderabad; Centre for Neural and Cognitive Sciences (B.S.), University of Hyderabad; and Department of Neurology (J.R.C.), Yashoda Hospitals, Hyderabad, India.
authors.forename: Suvarna
authors.initials: S
authors.lastname: Alladi
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Bak
authors.forename: Vasanta
authors.initials: V
authors.lastname: Duggirala
authors.forename: Bapiraju
authors.initials: B
authors.lastname: Surampudi
authors.forename: Mekala
authors.initials: M
authors.lastname: Shailaja
authors.forename: Anuj Kumar
authors.initials: AK
authors.lastname: Shukla
authors.forename: Jaydip Ray
authors.initials: JR
authors.lastname: Chaudhuri
authors.forename: Subhash
authors.initials: S
authors.lastname: Kaul
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D003704:Dementia / Q000453:epidemiology* / Q000503:physiopathology / Q000523:psychology*; D004522:Educational Status; D004641:Emigration and Immigration; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D019303:Multilingualism