Letters Onset of cognitive decline

Authors’ reply to Harwood, McCarthy, and Franke

BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e1050 (Published 14 February 2012) Cite this as: BMJ 2012;344:e1050
  1. Archana Singh-Manoux, research director123
  2. On behalf of Mika Kivimaki, M Maria Glymour, Alexis Elbaz, Claudine Berr, Klaus P Ebmeier, Jane E Ferrie, Aline Dugravot
  1. 1Institut National de la Santé et de la Recherche Médicale (INSERM), U1018, Centre for Research in Epidemiology and Population Health, Hôpital Paul Brousse, 94807 Villejuif Cedex, France
  2. 2Department of Epidemiology and Public Health, University College London, London, UK
  3. 3Centre de Gérontologie, Hôpital Ste Périne, AP-HP, France
  1. archana.singh-manoux{at}inserm.fr

The over-riding concern about our paper is that it propagates the tradition of emphasising decline and ignoring gains that occur with ageing.1 2 3 4 This was not our intention. We wanted to answer an important research question of whether cognitive decline occurs before the age of 60, and we had the rare opportunity of using longitudinal data—three assessments over 10 years—to do so. We used established statistical methods and most of the evidence, four of the five tests, shows a significant decline in all age groups. It would have been inappropriate to draw conclusions that were based on only the vocabulary test. It is worth highlighting that the analysis yielded “mean” decline in each age group (a sum of no decline, minor decline, and major decline); our view is that better understanding of cognitive ageing will come from closer attention to the heterogeneity in the rates of decline.

The timed component of the cognitive tests also attracted comment. Work demands and activities like cooking, shopping, driving, and conversation with family and friends require cognitive responses within a certain time frame. Cognitive test batteries used to study cognitive ageing are designed to assess this ability. It is important to recognise that these tests do not measure knowledge or wisdom. The finding that education does not influence the rate of cognitive decline is not new,5 6 but this does not imply that cognitive decline is natural or non-modifiable. Higher education is associated with lower risk and not the absence of risk of dementia.


Cite this as: BMJ 2012;344:e1050


  • Competing interests: None declared.