A person can have many benefits from being bilingual, for the brain, it can shorten recovery times from stroke, stave off cognitive decline associated with dementia and Alzheimer’s disease, and so on. Unfortunately, it seems that bilingualism can also significantly accelerate the deterioration into severe Alzheimer’s once symptoms manifest, as found by psychology researchers at Canada’s York University.

The researchers initially hoped to study how bilingualism could boost the brain’s cognitive reserve, which refers to its resilience to neurodegeneration – a greater cognitive reserve can, temporarily, mitigate the impacts of cognitive decline. About 158 patients who had mild cognitive impairment were divided into a bilingual/high cognitive reserve group or a monolingual/low cognitive reserve group, and assessed over five years to track their progression into Alzheimer’s. Surprisingly, the monolingual group made the transition in 2.6 years, while the bilingual group progressed rapidly, in just 1.8 years.

While both groups presented with the same level of cognitive function at the outset of the study, the researchers believe the Alzheimer’s pathology was steadily building up in the bilingual group, though they seemed fine.

Psychologist and professor, Ellen Bialystok, uses this analogy, “Imagine sandbags holding back the floodgates of a river – at some point the river is going to win. The cognitive reserve is holding back the flood but when the floodgates get completely washed out,these people will crash faster.”

Despite the bad news, the upside is that the greater cognitive reserve enables bilingual individuals to live without symptoms of the disease for longer, until that vital threshold is crossed, so it’s best to maintain such independent living as long as possible.