Numerous studies have been conducted on the ability of preventative measures such as exercise, in halting the march of cognitive impairment at old age. Unfortunately, however, although most are randomised controlled tests (universally regarded as the best study approach) and published in peer-reviewed journals by respected experts, there is significant disagreement between scientists about whether they are proof that a certain behaviour helps prevent cognitive impairment or not. Unhelpfully, evidence that any one preventative measure works is also elusive.

Experiments on exercise and cognitive improvement

A study conducted by researchers from the Maastricht University in the Netherlands and the University of British Columbia (UBC) in Canada found that when older women with mild cognitive impairment (MCI), which often becomes Alzheimer’s disease, exercised two times a week for six months, those that did resistance exercise or balance training, on average had a decrease in hippocampus (where memories are formed) size of 2%. Those that performed aerobic exercises however, saw a 4% increase in the size of the hippocampus.

In 2011, researchers from the Chinese University of Hong Kong conducted a randomised controlled trial to see if tai chi or stretching exercises helped slow down cognitive decline in individuals with MCI. The scientists found that both forms of exercise improved brain function but tai chi lowered the chance of developing dementia by 74%.

Carl Cotman, the director of the Institute for Brain Aging and Dementia at the University of California and his team conducted physical exercise activities on mice genetically engineered to develop Alzheimer’s-like pathology. "Our work and the work of others have converged on the point that exercise literally rejuvenates the aging brain," he said.

Another small trial conducted in America, by the University of Washington School of Medicine and the Veterans Affairs Medical Centre found that when usually sedentary elders with cognitive problems are made to exercise for six months, their ability to concentrate and perform complex tasks was far better than a control group who were only given stretching activities to do.

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Why do other well-respected experts feel this experimental proof is elusive?

In December of last year, the National Academies of Science, Engineering and Medicine in America formed a panel to examine 262 studies on the link between exercise and improved mental function and together they concluded that the evidence was “insufficient”. There were a number of different reasons for this.

For example, for the study conducted by the UBC, the Academies were concerned with the number of participants that dropped out of their exercise routines half way through – one fifth of the aerobics group dropped out. For the tai chi study, only 54% of the group stayed.

This is a problem because it suggests that those who felt no improvement in brain function dropped out which left only those who, for whatever reason, including random fluctuations in brain health, felt benefited. This unintentionally skews the result in favour of exercise for the brain. Study after study had dropout rates of 20-30%, if not more.

Another problem is selective reporting. “They would report using 10 tests and report results of only four. The suspicion, cynically, is that the outcomes they didn’t report looked worse and that they were cherry-picking,” said Dr Howard Fink, co-author of the evidence review by the Academies panel.

Duration of test time is also a significant problem. To effectively assess a behavioural habit such as diet or exercise, many years are needed. However, finding public funding for such long studies is difficult which means most studies are too short to be taken seriously.

What’s the rationale behind efforts to promote studies and preventive behaviour?

“I can imagine a practitioner thinking, well, it can’t hurt” to tell patients with MCI to try exercising, said Michelle Brasure, who led the team that reached the “insufficient evidence” conclusion for the National Academies. “From their point of view, why not recommend it?”

“I wouldn’t go to the bank with the claim” that exercise can keep MCI from progressing to dementia, said Dr Ronald Petersen, director of the Alzheimer’s Disease Research Centre at the Mayo Clinic. “But we thought it was a reasonable thing to say, especially since [exercise] doesn’t have a lot of risk. To be honest, we’re looking for something positive to tell people.”

Kenneth Kosik, a founder of Cognitive Fitness & Innovative Therapies, which counsels people on strategies to prevent dementia explains, "it's beyond me to understand why anyone would not want to endorse such ideas as long as we are honest and we tell people what the caveats are. Not doing anything for people at high risk is just being nihilistic"

As Professor Luke Drury of the Dublin Institute for Advanced Studies says, “disagreement is a core part of the scientific process” and should not be construed a weakness. “Absolute certainty is confined to mathematical proof, and even there it is a bit dodgy.” MIMS

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