Posted by: Cindy Tolan
Are there any ways of preventing or delaying the development of Alzheimer’s disease or other forms of age-associated dementia? While several previously published studies have suggested a protective effect for cognitive activities such as reading, playing games or attending cultural events, questions have been raised about whether these studies reveal a real cause-and-effect relationship or if the associations could result from unmeasured factors.
A Boston-based research team conducted a formal bias analysis and concluded that, while potentially confounding factors might have affected previous studies’ results, it is doubtful that such factors totally account for observed associations between cognitive activities and a reduced risk of dementia.
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 were 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 any 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. This 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 – whether a reduction in cognitive activity among those already in the long phase of cognitive decline that precedes Alzheimer’s dementia might have led to an apparent rather than a real causal relationship. The findings of that analysis could not rule out the possibility that reverse causation contributed substantially to the observed associations, but analyses restricted to studies with longer term follow-up might be better able to address this question, the group noted.
“Ultimately, clinical trials with long-term follow-up are the surest way to definitively address reverse causation,” says AlzRisk co-director Jennifer Weuve, MPH, ScD, of Boston University School of Public Health. “Trials could also confront the vexing question of whether training to improve specific cognitive skills has benefits that extend into everyday functions.”
The group also noted it is best for people to engage in cognitive activities that they find interesting and enjoyable for their own sake. There is no evidence that one kind of activity is better than another, so they cautioned against spending money on programs claiming to protect them against dementia.
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