Summary: While being bilingual delays the onset of dementia, the decline into full-blown Alzheimer’s disease is more rapid in those who speak two or more languages than in monolingual people.
Source: York University
A study by York University psychology researchers provides new evidence that bilingualism can delay symptoms of dementia.
Alzheimer’s disease is the most common form of dementia, making up 60 to 70 per cent of dementia cases. Of all activities with neuroplastic benefits, language use is the most sustained, consuming the largest proportion of time within a day. It also activates regions across the entire brain. Ellen Bialystok, Distinguished Research Professor in York’s Department of Psychology, Faculty of Health, and her team tested the theory that bilingualism can increase cognitive reserve and thus delay the age of onset of Alzheimer’s disease symptoms in elderly patients.
Their study is believed to be the first to investigate conversion times from mild cognitive impairment to Alzheimer’s disease in monolingual and bilingual patients. Although bilingualism delays the onset of symptoms, Bialystok says, once diagnosed, the decline to full-blown Alzheimer’s disease is much faster in bilingual people than in monolingual people because the disease is actually more severe.
“Imagine sandbags holding back the floodgates of a river. At some point the river is going to win,” says Bialystok. “The cognitive reserve is holding back the flood and at the point that they were when they were diagnosed with mild cognitive impairment they already had substantial pathology but there was no evidence of it because they were able to function because of the cognitive reserve. When they can no longer do this, the floodgates get completely washed out, so they crash faster.”
In the five-year study, researchers followed 158 patients who had been diagnosed with mild cognitive impairment. For the study, they classified bilingual people as having high cognitive reserve and monolingual people as having low cognitive reserve.
Patients were matched on age, education, and cognitive level at the time of diagnosis of mild cognitive impairment. The researchers followed their six-month interval appointments at a hospital memory clinic to see the point at which diagnoses changed from mild cognitive impairment to Alzheimer’s disease. The conversion time for bilinguals, 1.8 years after initial diagnosis, was significantly faster than it was for monolinguals, who took 2.6 years to convert to Alzheimer’s disease. This difference suggests that bilingual patients had more neuropathology at the time they were diagnosed with mild cognitive impairment than the monolinguals, even though they presented with the same level of cognitive function.
These results contribute to the growing body of evidence showing that bilinguals are more resilient in dealing with neurodegeneration than monolinguals. They operate at a higher level of functioning because of the cognitive reserve, which means that many of these individuals will be independent longer, Bialystok says. This study adds new evidence by showing that the decline is more rapid once a clinical threshold has been crossed, presumably because there is more disease already in the brain.
“Given that there is no effective treatment for Alzheimer’s or dementia, the very best you can hope for is keeping these people functioning so that they live independently so that they don’t lose connection with family and friends. That’s huge.”
About this neuroscience research article
Source: York University Media Contacts: Anjum Nayyar – York University Image Source: The image is in the public domain.
Conversion of Mild Cognitive Impairment to Alzheimer Disease in Monolingual and Bilingual Patients
Purpose: Conversion rates from mild cognitive impairment (MCI) to Alzheimer disease (AD) were examined considering bilingualism as a measure of cognitive reserve.
Methods: Older adult bilingual (n=75) and monolingual (n=83) patients attending a memory clinic who were diagnosed with MCI were evaluated for conversion to AD. Age of MCI and AD diagnoses and time to convert were recorded and compared across language groups. Patients: Patients were consecutive patients diagnosed with MCI at a hospital memory clinic.
Results: Bilingual patients were diagnosed with MCI at a later age than monolingual patients (77.8 and 75.5 y, respectively), a difference that was significant in some analyses. However, bilingual patients converted faster from MCI to AD than monolingual patients (1.8 and 2.8 y, respectively) resulting in no language group difference in age of AD diagnosis. This relationship held after accounting for education, cognitive level, immigration status, and sex.
Discussion: The findings suggest that greater cognitive reserve as measured by language status leads to faster conversion between MCI and AD, all else being equal.
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