Can exercise prevent dementia? Molecular Psych.Aug.2013.

15.10.2013

Physical activity is known to have positive effects on numerous disorders. Is it applicable to dementia as well? BM Brown, J J Peiffer and RN Martins provide a comprehensive review of our present knowledge in this area.

Many studies indicate that physical activity or exercise may enhance cognitive function and delay the onset of Alzheimer’s disease (AD) and other dementias. Spirduso  et al published the first study in 1978 showing better reaction time in physically active older men. Since then numerous studies have shown better verbal memory, executive functioning, attention and global scores of cognitive function  among those more physically active. One study has suggested that intense physical activity, rather than total activity, was associated with better performance in numerous cognitive domains.However, another study, recently has shown that moderate (but not light or vigorous) exercise at mid-life or late-life was associated with a reduced risk of mild cognitive impairment.

Barnes et al used objective measures of activity ( rather than questionnaires) and demonstrated that individuals in the highest quartile of daytime movement performed better on the trail making test and the Mini Mental State Examination than those in the lowest quartile. Another study showed that those with lowest baseline cardio-respiratory fitness performed the worst on all cognitive tests conducted 6 years later, and also exhibited the greatest decline on the Mini Mental State Examination.

Larson et al’s study showed that individuals exercising three or more times a week were less likely to develop dementia at follow-up. Scarmeas et al. also observed a similar association. (Those in the ‘much’ physical activity group and ‘some’ physical activity group were less likely to develop AD, compared with those that reported no participation in any physical activities).  Buchman et al used objective measures of activity and demonstrated that higher levels of total daily physical activity were associated with decreased risk of AD.

It is worthwhile to note that there are some negative studies as well.

Do interventional studies also support this notion? These studies are troubled by the confounding factors like diet, medications, general health and lifetime health habits. Kramer et al. showed that individuals participating in the walking intervention had improved scores on an executive function task (task switching) compared with the stretching/toning group.RCT by Baker et al. observed that after 6 months of aerobic exercise, female participants demonstrated improved performance on executive function tasks.

Life-p study did not show benefit for exercise intervention (which involved strength, balance, flexibility and aerobic training over a period of 6 month), it is possible that the intensity of the aerobic intervention (walking) was not sufficient to induce significant cognitive differences between the groups.

Lautens-chlager et al. examined the influence of a 24-week exercise intervention programme consisting of 150 min of moderate- intensity exercise over 3 days per week on cognitive decline among those with MCI over 18 months. The  intervention group improved by 1.3 points on the Alzheimer Disease Assessment Scale (ADAS-COG).

What kind of exercise is useful?

One meta-analysis has highlighted the possibility that combined aerobic and strength training interventions may give a greater degree of cognitive function improvement, compared with aerobic fitness alone

Meta analytic data:

1.Colcombe and Kramer, 2003: Fitness training was found to increase cognitive performance by an average 0.5 of a standard deviation

2.Paterson and Warburton 2010 : Positive association between physical activity and cognitive function was found in 71% of the investigated studies

3.Sofi et al. 2011: included 15 cohort studies. High levels of exercise induced the greatest protective effects with a hazard ratio of 0.62.

4. Hamer  2009: ( compiled all epidemiological studies): The relative risk of dementia in the highest physical activity groups compared with the lowest or control groups was calculated to be 0.72  and the relative risk of AD was found to be 0.55.

Is the benefit mainly or more in females? Studies generally support this notion. (It is not to say that men do not show benefit). It is possible that women benefit by higher increase in hormones secondary to exercise ( for e.g. testosterone).

How do exercise improve or prevent cognitive decline? The possible mechanism with variable degree of evidence include 1. Activity reduce amyloid-b levels 2. Activity can reduce brain atrophy and induce functional network changes 3. Exercise increase levels of growth factors  (eg BDNF) and neurotransmitters.

Conclusions: 

physical activity can help maintain superior cognitive functioning as well as modify the risk of cognitive decline. Little is known about the underlying mechanism behind this.

Summary of the article: 

Multiple effects of physical activity on molecular and cognitive signs of brain aging: can exercise slow neurodegeneration anddelay Alzheimer’s disease? Brown BM, Peiffer JJ, Martins RN. Mol Psychiatry. 2013 Aug;18(8):864-74

 

 

 

 

 

 

 

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