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Physical activity, cognitive decline, and risk of dementia: 28 year follow-up of Whitehall II cohort study

BMJ 2017; 357 doi: https://doi.org/10.1136/bmj.j2709 (Published 22 June 2017) Cite this as: BMJ 2017;357:j2709
  1. Séverine Sabia, research associate1 2,
  2. Aline Dugravot, statistician1,
  3. Jean-François Dartigues, professor3,
  4. Jessica Abell, research associate1 2,
  5. Alexis Elbaz, research professor1,
  6. Mika Kivimäki, professor2,
  7. Archana Singh-Manoux, research professor1 2
  1. 1Centre for Research in Epidemiology and Population Health, INSERM U1018, Université Paris-Saclay, Hôpital Paul Brousse, Paris, France
  2. 2Department of Epidemiology and Public Health, University College London, London, UK
  3. 3INSERM U1219, University of Bordeaux, Bordeaux, France
  1. Correspondence to: S Sabia severine.sabia{at}inserm.fr
  • Accepted 31 May 2017

Abstract

Objective To test the hypotheses that physical activity in midlife is not associated with a reduced risk of dementia and that the preclinical phase of dementia is characterised by a decline in physical activity.

Design Prospective cohort study with a mean follow-up of 27 years.

Setting Civil service departments in London (Whitehall II study).

Participants 10 308 participants aged 35-55 years at study inception (1985-88). Exposures included time spent in mild, moderate to vigorous, and total physical activity assessed seven times between 1985 and 2013 and categorised as “recommended” if duration of moderate to vigorous physical activity was 2.5 hours/week or more.

Main outcome measures A battery of cognitive tests was administered up to four times from 1997 to 2013, and incident dementia cases (n=329) were identified through linkage to hospital, mental health services, and mortality registers until 2015.

Results Mixed effects models showed no association between physical activity and subsequent 15 year cognitive decline. Similarly, Cox regression showed no association between physical activity and risk of dementia over an average 27 year follow-up (hazard ratio in the “recommended” physical activity category 1.00, 95% confidence interval 0.80 to 1.24). For trajectories of hours/week of total, mild, and moderate to vigorous physical activity in people with dementia compared with those without dementia (all others), no differences were observed between 28 and 10 years before diagnosis of dementia. However, physical activity in people with dementia began to decline up to nine years before diagnosis (difference in moderate to vigorous physical activity −0.39 hours/week; P=0.05), and the difference became more pronounced (−1.03 hours/week; P=0.005) at diagnosis.

Conclusion This study found no evidence of a neuroprotective effect of physical activity. Previous findings showing a lower risk of dementia in physically active people may be attributable to reverse causation—that is, due to a decline in physical activity levels in the preclinical phase of dementia.

Footnotes

  • Contributors: ASM and SS developed the hypothesis and study design. SS and AD did the statistical analysis. SS wrote the first and successive drafts of the manuscript. All authors contributed to study concept and design, analysis and interpretation of data, and drafting or critical revision of the manuscript for important intellectual content or additionally to data acquisition. ASM and MK obtained funding for the Whitehall II study. SS, AD, and ASM had full access to the data and take responsibility for the integrity of the data and the accuracy of the data analysis. SS is the guarantor.

  • Funding: The Whitehall II study is supported by grants from the US National Institutes on Aging (R01AG013196; R01AG034454), the UK Medical Research Council (MRC K013351), and the British Heart Foundation (RG/13/2/30098). The sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of this manuscript.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at http://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.

  • Ethical approval: University College London Hospital Committee on the Ethics of Human Research, reference number 85/0938. Written informed consent from participants and research ethics approvals were renewed at each contact.

  • Data sharing: Whitehall II data, protocols, and other metadata are available to the scientific community. Please refer to the Whitehall II data sharing policy at https://www.ucl.ac.uk/whitehallII/data-sharing.

  • Transparency declaration: The lead author affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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