The last time that NIH requested a review of the data on preventing cognitive decline in old age (including Mild Cognitive Impairment, Alzheimer’s type dementia, and “usual” age-related cognitive deterioration) was in 2010. At that time, the systematic review of the published literature (performed by the Agency for Healthcare Research and Quality) and the associated state of the science conference (convened by NIH) concluded there was insufficient evidence to make any recommendations about interventions to prevent cognitive decline and dementia.
Now, the NIA has asked the National Academies of Science, Engineering, and Medicine to commission a new systematic review of the data and, based on that review, to issue recommendations about prevention. Its report, optimistically entitled, “Preventing Cognitive Decline and Dementia: A Way Forward,” was just released. Alas, while the commission bent over backwards to find beneficial interventions, adding observational, non-experimental studies, risk factor analysis, and neurobiological work to the randomized controlled trials (RCTs) that were supposed to provide the evidence for their conclusions, it was forced to conclude, once again, that the review “identified no specific interventions that are supported by sufficient evidence to justify mounting out an assertive public health campaign to encourage people to adopt them for the purpose of preventing cognitive decline and dementia.” The best the group could come up with was that the review did “find some degree of support for the benefit of three classes of intervention: cognitive training, blood pressure management in people with hypertension, and increased physical activity.
If we examine these three domains, what we find is not entirely encouraging. The arena of cognitive training (brain games, crossword puzzles, studying a foreign language, etc.) had the greatest degree of evidence. There is good evidence that it can improve performance in a trained task—that is, if you work at generating synonyms for words over and over again, you will get better at finding synonyms, at least in the short term. What is less clear is whether the benefits are sustained, whether training in one domain yields benefits in other domains, and whether it translates at all into improvement in daily functioning, in areas such as shopping, cooking, or paying bills. The good news, such as it is, about cognitive training, derives principally from one study, the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE), which provides moderately strong evidence of effectiveness in the training domain after 2 years but low strength evidence after 5 or 10 years. The improvements that were found failed to translate into areas other than the one where training was provided.
Perhaps surprisingly, given the strong evidence that blood pressure control in people with hypertension is beneficial in preventing stroke and coronary artery disease, vigorous blood pressure treatment did not so readily translate into prevention or delay of any form of cognitive decline in old age. One British study did show efficacy. Given that blood pressure treatment is already recommended for other reasons, encouraging its use in the hope that it might also help fend off cognitive decline evidently seemed harmless enough to the committee.
The story on exercise is similar to that on blood pressure control: the RCT data are inconsistent, but there’s at least some data that shows a positive effect. Exercise studies are problematic because they so often utilize different forms of exercise and prescribe varying duration and frequency of exercise. Nonetheless, given the evidence that exercise is useful to promote mobility and to prevent depression, and that some studies find it beneficial in preventing cognitive decline, the committee opted to include exercise in its short list of interventions for which there is “some degree of support.”
The main justification, it seems to me, for subtitling this report “A Way Forward” is the section on recommendations for future research. The areas that have shown some promise deserve further study. And that study, as well as all other avenues that might be pursued, should be methodologically sound. That means acknowledging the deficiencies of existing work and avoiding those flaws in the future.