March 30, 2011 — Multilingualism does not protect against the onset of Alzheimer's disease (AD) according to an analysis from the Nun study — a longitudinal study of aging and AD — where AD was rigorously defined by both neuropathological and clinical criteria.
Presented here at the Alzheimer's Disease International (ADI) 26th International Conference, research by Erica Hack, a master's of science student, University of Waterloo, Ontario, Canada, and colleagues found that regardless of the outcomes definitions there was no significant difference in dementia outcomes between study subjects who were multilingual and those who were not.
"There are a lot of unique aspects to the Nun study that add another dimension to the relationship [between multilingualism and AD]," Ms. Hack told Medscape Medical News.
Key among them, she added, is that researchers had access to the brains of participants in the Nun study "so we were able to look at Alzheimer's neuropathology, which is unique because not many other studies have had brain donation as part of their protocol."
The Nun study included 678 nuns, 75 years and older, from the School Sisters of Notre Dame in the United States. Data on multilingualism were available for 507 of them. Multilingualism was defined as speaking 2 or more languages fluently.
In addition, said Ms. Hack, the "sisters were highly educated." More than 90% were teachers and few (<7%) were immigrants to the United States. Most were very long lived. The mean age at death for the overall cohort was approximately 90 years.
The nuns were initially assessed between 1991 and 1993 and underwent 12 waves of annual cognitive assessments. Outcomes included clinical dementia and clinical dementia plus AD neuropathology.
ApoE4 Key Predictor
The diagnosis of clinical dementia was based on both the performance on a Consortium to Establish a Registry for Alzheimer's Disease (CERAD) battery of tests and impairment in activities of daily living.
AD neuropathology was defined using 2 different criteria: CERAD and National Institute of Aging–Reagan (NIA-Reagan). Remarkably, among 171 subjects assessed using the CERAD criteria — 116 of whom developed AD and 55 who did not — almost three-quarters of both groups reported they were multilingual.
Similar proportions of subjects assessed using the NIA-Reagan criteria (n = 197) also reported they were multilingual. Among those assessed by clinical dementia criteria (n = 408), the proportion who were multilingual among non-AD subjects vs those with dementia was again very similar.
The unadjusted odds ratio of developing AD among participants who reported having 2 or more languages was 1.2 using the CERAD plus clinical dementia outcome and 0.86 using the National NIA-Regan plus clinical dementia outcome compared with nuns who did not report having 2 or more languages. Multilingualism was also not significantly associated with clinical dementia at an unadjusted odds ratio of 1.15.
Perhaps not surprisingly, the key factor predicting the development of AD in the Nun study was the presence of the ApoE4 allele. Among those assessed by the CERAD criteria, the allele was present in more than 38% of AD subjects vs only about 7% in non-AD controls.
Some 43% of subjects assessed by the NIA-Reagan criteria also possessed the gene vs about 9% of normal controls. For those assessed by clinical dementia criteria, the gene was present in 32% of AD subjects vs 18% of non-AD controls.
Age at death was also significantly associated with AD.
Table. Factors That Predict the Development of Alzheimer's Disease (AD)
|CERAD (Normal [n = 55] and AD [n = 116])||NIA-Reagan (Normal [n = 92] and AD [n = 105])||Clinical Dementia (Normal [n = 210] and Dementia [n = 198])|
|Multilingualism||Normal: 72.7%; AD: 75.9%||Normal: 71.7%; AD: 68.6%||Normal: 70.9%; AD: 73.7%|
|APOE *E4 allele present||Normal: 7.3%; AD: 38.8% (P < .0001)||Normal: 8.7%; AD: 42.9% (P < .0001)||Normal: 18.1%; AD: 31.8% (P < .05)|
Age at death
|Normal: 89.4; AD: 92.3 (P < .001)||Normal: 90.2; AD: 91.8 (P < .05)||Normal: 89.89; AD: 92.3 (P < .001)|
CERAD = Consortium to Establish a Registry for Alzheimer's Disease; NIA-Reagan = National Institute of Aging–Reagan
"Regardless of the neuropathological criterion used, multilingualism was not significantly associated with AD," the investigators concluded. However, they added that future studies should aim to examine whether there is a relationship between multilingualism and a delay in onset or severity of AD.
Commenting on the findings for Medscape Medical News, J.B. Orange, PhD, School of Communications Sciences and Disorders, University of Western Ontario, London, Canada, said the study left a number of unanswered questions.
"For example, how did they define multilingualism?" he asked.
Dr. Orange added that data on multilingualism were self-reported and there were no objective measures verifying the level of proficiency achieved among individuals who spoke at least 2 languages.
"The other issue is, how often did these sisters use those languages and in what context?" Dr. Orange added. In other words, did subjects use multiple languages consistently throughout life in work and social settings, or did they largely revert to their dominant language and use other languages only sporadically.
"If you learned both languages in childhood and continued to use both languages at work and in social settings, that would suggest your cognitive reserve is being maximized each day," Dr. Orange said.
On the other hand, "even though you might be bilingual, that does not necessarily mean you are continually maximizing the full potential of both of those languages," he added.
It is believed that synaptic connections may be stimulated by long-term use of multiple languages, thereby enhancing cognitive reserve and lessening the impact of AD should someone develop it.
The study was funded by the University of Kentucky and the Kleberg Foundation. Ms Hack, her coinvestigator Dr. Tyas, and Dr. Orange have disclosed no relevant financial relationships.
Alzheimer's Disease International (ADI) 26th International Conference: Abstract P099. Presented March 29, 2011.
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Cite this: Speaking Multiple Languages Not Protective Against Alzheimer's - Medscape - Mar 30, 2011.