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Physical Activity, Cognitive Decline & Dementia

BMJ; ePub 2017 Jun 22; Sabia, Dugravot, et al

Publish date:

Physical activity does not have a protective effect for cognitive decline or risk of dementia, according to a recent study. The prospective cohort study included 10,308 participants aged 35 to 55 years at study inception from 1985 to 1988. Exposures included time spent in mild, moderate to vigorous, and total physical activity assessed 7 times between 1985 and 2013. Cognitive tests were administered up to 4 times from 1887 to 2013, and incident dementia cases (n=329) were identified until 2015. Researchers found:

  • There were no associations between physical activity and subsequent 15-year cognitive decline.
  • Similarly, Cox regression showed no association between physical activity and the risk of dementia over an average 27-year follow-up.
  • Trajectories of physical activity showed no difference between dementia cases and non-cases in the 28 to 10 years before diagnosis, with decline in physical activity starting up to 9 years before diagnosis.

Citation:

Sabia S, Dugravot A. Dartigues JF, et al. Physical activity, cognitive decline, and risk of dementia: 28-year follow-up of Whitehall II cohort study. [Published online ahead of print June 22, 2017]. BMJ. 2017;357:j2709. doi:10.1136/bmj.j2709.

Commentary:

Many studies have shown a relationship between increased physical activity and decreased likelihood of developing dementia. The potential problem with studies that show this correlation is that as an individual begins to develop dementia, they may begin to restrict their activities. Therefore, short-term studies that show a relation between decreased physical activity and dementia may only be measuring the effect, rather than the cause of dementia. This is called reverse correlation. The current study attempted to control for that possibility by having 28 years of follow-up. By looking at the question over a long period of time, it demonstrated that increased physical activity 10 to 28 years prior to the diagnosis of dementia did not seem to decrease the likelihood of developing dementia. The relationship seen between decreased physical activity and dementia starting 9 years prior to the diagnosis of dementia may still be causal, or may actually represent an effect of dementia on activity level. —Neil Skolnik, MD

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