title: Retirement age and the age of onset of Alzheimer's disease: results from the ICTUS study.
abstract: OBJECTIVE
  To test whether deferred retirement is associated with delayed onset of Alzheimer's disease (AD), and, if so, to determine whether retirement age still predicts the age at onset of AD when two potential biases are considered.
  
  
  METHODS
  The study sample was gathered from the Impact of Cholinergic Treatment Use/Data Sharing Alzheimer cohort (ICTUS/DSA), a European study of 1,380 AD patients. Information regarding retirement age, onset of symptoms and covariates was collected at baseline whereas age at diagnosis was gathered from the patient's medical record prior to study entry. Linear mixed models, adjusted for gender, education, occupation, center, country, household income, depression and cardiovascular risk factors were conducted on 815 patients.
  
  
  RESULTS
  (1) The global analyses (n = 815) revealed that later age at retirement was associated with later age at diagnosis (β = 0.31, p < 0.0001); (2) once the selection bias was considered (n = 637), results showed that this association was weaker but remained significant (β = 0.15, p = 0.004); (3) once the bias of the reverse causality (i.e., the possibility that subjects may have left the workforce due to prior cognitive impairment) was considered (n = 447), the effect was no longer significant (β = 0.06, p = 0.18).
  
  
  CONCLUSIONS
  The present study supports that there is an association between retirement age and age at onset of AD. However, the strength of this association appears to be overestimated due to the selection bias. Moreover, the causality issue remains unresolved. Further prospective investigations are mandatory in order to correctly address this question.
authors.affiliation: University of Liège, Psychology of Aging Unit, Liège, Belgium.
authors.forename: Catherine
authors.initials: C
authors.lastname: Grotz
authors.affiliation: INSERM, Unit 897, F-33076 Bordeaux, France; University of Bordeaux, F-33076, Bordeaux, France.
authors.forename: Luc
authors.initials: L
authors.lastname: Letenneur
authors.affiliation: Maastricht University, Research Center for education and labour force market (ROA), Maastricht, The Netherlands; Centre d'études de Populations, de Pauvreté et de Politiques Socio-Économiques/ International Networks for Studies in Technology, Environment, Alternatives, Development (CEPS/INSTEAD), Esch-sur-Alzette, Luxembourg.
authors.forename: Eric
authors.initials: E
authors.lastname: Bonsang
authors.affiliation: INSERM, Unit 897, F-33076 Bordeaux, France; University of Bordeaux, F-33076, Bordeaux, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Amieva
authors.affiliation: INSERM, Unit 897, F-33076 Bordeaux, France; University of Bordeaux, F-33076, Bordeaux, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Meillon
authors.affiliation: University of Liège, Cognitive and Behavioral Neuroscience Center, Liège, Belgium.
authors.forename: Etienne
authors.initials: E
authors.lastname: Quertemont
authors.affiliation: University Hospital of Liège, Memory Center, Belgium, Liège, Belgium.
authors.forename: Eric
authors.initials: E
authors.lastname: Salmon
authors.affiliation: University of Liège, Psychology of Aging Unit, Liège, Belgium; University Hospital of Liège, Memory Center, Belgium, Liège, Belgium.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Adam
mesh_terms: D000367:Age Factors; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000453:epidemiology*; D015897:Comorbidity; D005060:Europe; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012179:Retirement