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Proof That Exercise Defeats Dementia - Or Is It?

Students often say "proof" or "researchers proved...".  Here's a study that might get them re-thinking this tendency to use this word.


A study that appeared in the journal Neurology entitled, Midlife cardiovascular fitness and dementia
A 44-year longitudinal population study in women and nicely summarized here by CNN, did the following and found some convincing results:


  1. 191 Swedish women (38 to 66 years old) were given tests of their cardiovascular fitness
  2. During the tests (exercising on a stationary bike) their blood pressure was monitored and they were connected to a electrocardiograph.
  3. Based on their results, “the women were separated into three groups: Fifty-nine were in the "low fitness" group, 92 were "medium fitness," and 40 were "high fitness."
  4. The exercise tests were given in 1968 and the women were followed for 44 years to see who was diagnosed with dementia.

Results: overall, 23% of the women developed dementia.  However, 45% of those in the "low fitness" group developed dementia.


Proof, then, that exercise can prevent dementia?


Actually, this study, as impressively carried out as it is, cannot lead us to confident causal conclusions about the role of exercise in warding off dementia. The results are correlational at best and as we know, correlation is not causation.


Ask your students: are there alternative explanations for the results?


Have your students work in groups of 2-3 to see if they can generate some alternative hypotheses to the results. Here are some:


  1. Isn't it possible that the high fitness women also ate healthier foods during their lives? If so, which foods benefited them the most? We don't know because again, the researchers did not ask the women what kinds of foods they ate during the study period.
  2. There was no random assignment of subjects to conditions. The women were assigned to one of the three groups (low, medium or high fitness) based on their scores on a cardiovascular test. So as a result, we don't know WHY the women were of different fitness levels. We can easily assume that the women in the high fitness levels were more active in their lives - but could their better fitness levels have been genetic?
  3. The researchers don't know what the women did in their daily lives from 1968 to 2012, so how do they know if the high fitness women continued to be active?
  4. Isn’t it also possible that the high fitness women benefited not so much from exercise, but from the social interaction that usually accompanies exercise? (other research has found that social interaction is also very important to warding off dementia).

So while the study can be said to “provide some evidence” in favor of a causal link between exercise and dementia, it cannot offer “proof”. We really don’t know - for sure - what those high fitness women did in their lives that resulted in their lower levels of dementia.