Cognitive Activity Can Reduce Dementia Risk.

In recent years, several studies have suggested that cognitive activities such as reading, playing games or attending cultural events may help to prevent or delay the development of Alzheimer’s disease or other forms of age-associated dementia. But questions have been raised about whether those studies reveal a real cause-and-effect relationship, or if the associations could result from unmeasured factors.

To address those questions, a Boston-based team that included a School of Public Health researcher conducted a formal bias analysis, concluding that, while potentially confounding factors might have affected previous studies’ results, it was doubtful that such factors totally accounted for observed associations between cognitive activities and a reduced risk of dementia. The findings lend support to a potential role for late-in-life cognitive activity in preventing Alzheimer’s disease.

The study, in the September issue of the journal Epidemiology, was led by researchers from the Massachusetts General Hospital’s Department of Psychiatry and the Harvard T.H. Chan School of Public Health. Jennifer Weuve, a research associate of epidemiology and co-director of the AlzRisk database, was a co-author.

The research team analyzed 12 peer-reviewed epidemiologic studies that examined the relationship between late-in-life cognitive activities and the incidence of Alzheimer’s disease or other forms of dementia. The studies, selected on the basis of pre-specified criteria for the AlzRisk database, included almost 14,000 individual participants and consistently showed a benefit, sometimes substantial, for cognitive activity.

Since observational studies are likely to be confounded by unmeasured factors—such as participants’ socioeconomic level or the presence of conditions like depression – the researchers also conducted a bias analysis designed to evaluate how much such factors might influence reported associations between the amount of cognitive activity and dementia risk. The analysis indicated that bias due to unmeasured factors was unlikely to account for all of the association, because the impact of such factors is likely to be considerably smaller than the observed effect.

The group also investigated the possible role of reverse causation—i.e., whether a reduction in cognitive activity among those already in the phase of cognitive decline that precedes Alzheimer’s might have influenced the findings of an association. That analysis could not rule out the possibility that reverse causation contributed substantially to the observed associations. Analyses restricted to studies with longer-term follow-up might be better able to address the question, the authors said.

“Ultimately, clinical trials with long-term follow-up are the surest way to definitively address reverse causation,” Weuve said. “Trials could also confront the vexing question of whether training to improve specific cognitive skills has benefits that extend into everyday functions. But not every question about cognitive activity is well suited for a trial. To fill those gaps, innovations in epidemiology, such as the analytic techniques used in this study, should help us get even greater insights from available observational data.”