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. 2012 Jan 5:344:d7622.
doi: 10.1136/bmj.d7622.

Timing of onset of cognitive decline: results from Whitehall II prospective cohort study

Archana Singh-Manoux  1 , Mika Kivimaki, M Maria Glymour, Alexis Elbaz, Claudine Berr, Klaus P Ebmeier, Jane E Ferrie, Aline Dugravot
Affiliations

Timing of onset of cognitive decline: results from Whitehall II prospective cohort study

Archana Singh-Manoux et al. BMJ. .

Abstract

Objectives: To estimate 10 year decline in cognitive function from longitudinal data in a middle aged cohort and to examine whether age cohorts can be compared with cross sectional data to infer the effect of age on cognitive decline.

Design: Prospective cohort study. At study inception in 1985-8, there were 10,308 participants, representing a recruitment rate of 73%.

Setting: Civil service departments in London, United Kingdom.

Participants: 5198 men and 2192 women, aged 45-70 at the beginning of cognitive testing in 1997-9.

Main outcome measure: Tests of memory, reasoning, vocabulary, and phonemic and semantic fluency, assessed three times over 10 years.

Results: All cognitive scores, except vocabulary, declined in all five age categories (age 45-49, 50-54, 55-59, 60-64, and 65-70 at baseline), with evidence of faster decline in older people. In men, the 10 year decline, shown as change/range of test × 100, in reasoning was -3.6% (95% confidence interval -4.1% to -3.0%) in those aged 45-49 at baseline and -9.6% (-10.6% to -8.6%) in those aged 65-70. In women, the corresponding decline was -3.6% (-4.6% to -2.7%) and -7.4% (-9.1% to -5.7%). Comparisons of longitudinal and cross sectional effects of age suggest that the latter overestimate decline in women because of cohort differences in education. For example, in women aged 45-49 the longitudinal analysis showed reasoning to have declined by -3.6% (-4.5% to -2.8%) but the cross sectional effects suggested a decline of -11.4% (-14.0% to -8.9%).

Conclusions: Cognitive decline is already evident in middle age (age 45-49).

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Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

Figures

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Decline in cognitive test scores over 10 years (% change=change/range of text×100) as function of baseline age cohort in men and women, estimated from linear mixed models. P values denote test for linear trend across age categories, derived by entering them as continuous variable
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