America’s Bilingual Counties Have Lower Rates of Alzheimer’s. Now Scientists Want to Know Why.

Researchers are unable to stop examining a subtle pattern that appears in the public health data. Alzheimer’s rates are typically lower than the national average in counties where a significant portion of the population speaks two languages at home. Not always significantly lower. But consistently enough that it no longer seems like a coincidence.

On a Tuesday afternoon, if you stroll through a neighborhood in Hialeah, which is just outside of Miami, you will hear Spanish and English mixed together at the same bus stop, sometimes within the same sentence. Without appearing to notice, the older women with grocery bags alternate between the two. It’s the kind of thing you ignore until a scientist informs you that it may be changing the structure of their brains.

A few years ago, doctors in Northern Italy scanned 85 patients at roughly the same stage of probable Alzheimer’s disease. This imaging work is part of the data that has researchers leaning in. There were forty-five bilingual Germans and Italians. Forty spoke only one language. They appeared similar on paper. They didn’t, inside their skulls. The bilingual patients’ brains had more damage and a lower metabolism in the areas you would expect to see lit up in dementia, and they were, on average, five years older than the monolinguals with the same degree of impairment. To put it simply, they were dealing with more.

That’s the part that surprises people. The illness is not prevented by bilingualism. The tangles and plaques are still visible. The brain appears to continue working, almost obstinately, for a longer period of time. This type of neural cushioning accumulated over decades of switching, inhibiting, choosing, and code-mixing is known by researchers as cognitive reserve. A bilingual person is subtly using some background system each time they reach for the appropriate word in the appropriate language.

Although no one is making generalizations just yet, it’s possible that the county-level statistics in the US are showing something similar. Given their demographics, Miami-Dade, El Paso, portions of Queens, and large portions of the Rio Grande Valley all exhibit lower-than-expected dementia incidence. It is not entirely explained by access to care or income. Diet doesn’t either. Although no one can pinpoint the precise amount, some neurologists believe that language use is actually contributing to this.

Of course, skepticism is justified. In the United States, bilingualism is associated with immigration, closer family ties, and multigenerational households where grandparents continue to provide care and converse well into their eighties. It is really difficult to separate the language effect from the social one. The dementia delay has not been replicated in some studies. It has been strongly found by others. There is still debate in the field.

This type of imaging work is a crucial piece of the puzzle, according to Dr. Clare Walton of the Alzheimer’s Society, not only because it connects bilingualism to lower risk but also because it starts to explain why. Lifelong bilinguals seem to have stronger connections between executive control-related brain regions. They are more adept at avoiding damage.

Another correlation is not what scientists are looking for right now. The mechanism is what they want. They want to know if learning a second language at age 50 provides any of the same level of protection as speaking two languages as a child. They want to know if it’s the vocabulary load, the switching, or just the social entanglement that comes with fluency. As this research develops, it’s difficult not to feel that millions of Americans’ daily lives contain something truly beneficial that is just waiting to be fully comprehended.