Bilingualism has many benefits, including the opportunity to communicate across cultures. However, some research has found that speaking more than one language has advantages that go far beyond communication. Being bilingual has been correlated with better brain functioning and a reduced risk of dementia.
The general consensus is that it may be possible for the symptoms of Alzheimer's to be delayed in mentally fit, active brains because mental "exercise" may create cognitive reserve.
The idea behind cognitive reserve is that it "strengthens the muscles" of the brain, fostering improved connections between brain neurons and an increased ability to compensate for dysfunction in the brain. One way to give your brain a great workout is to learn and use another language.
According to a review of research, multiple studies have shown a delay in Alzheimer's and dementia symptoms in those who were bilingual. On average, people who were bilingual developed symptoms of dementia at an average age of five years older than those who spoke only one language.
To learn more about bilingualism and the brain, researchers compared brain imaging of bilingual persons to those of monolinguals (those who spoke one language).
All participants in the study had probable Alzheimer's disease and demonstrated similar levels of cognitive functioning. The researchers also took into account age, education, jobs, and gender to ensure that any difference identified could not be attributed to those factors.
The results of the study found that the bilinguals' brains displayed far more damage on the scans related to Alzheimer's disease than the monolinguals, yet their overall cognitive functioning was approximately the same as evidenced by similar results on three different cognitive tests.
How can this be? It goes back to the idea of cognitive reserve. Although it appears that the effects of Alzheimer's had been developing for some time in their brains, the symptoms of Alzheimer's were far less progressed than would have been expected. The bilingual individuals were somehow able to compensate or utilize different pathways despite having significant physical damage in their brains.
Further research published in the journal Neuropsychology studied the effects of being bilingual on the executive functioning of two groups of participants: 75 people with a diagnosis of Alzheimer's disease and 74 with a diagnosis of mild cognitive impairment, a condition that sometimes progresses into Alzheimer's disease. Executive functioning was tested using three different tests: the Trail-Making test, a color-word interference test (like the Stroop test) and the verbal fluency test. Results indicated that participants who were bilingual developed impaired executive functioning several years later than those who spoke only one language.
Other research has found that individuals who are bilingual recover cognitive ability more effectively following a stroke than those who speak only one language.
Strokes place people at risk for vascular dementia, and depending upon the location of the stroke, language and cognitive abilities are affected.
A study outlined in PLOS One looked at the effects of being multilingual—that is, knowing and using more than two languages. The study consisted of participants who displayed some beginning cognitive impairment but had not been diagnosed with dementia. The researchers found that the participants who practiced more than two languages had a reduced risk of cognitive decline—in fact, up to seven times the protection against cognitive decline as did those who used only two languages.
As we age, our brains tend to gradually atrophy (decrease in size) over time. Furthermore, brain volume, both overall and in specific areas of the brain, has been tied to cognitive functioning.
A group of researchers studied how brain volume of bilinguals compared to that of monolinguals. They found that volume of both gray matter and white matter in the brain was larger in those who were bilinguals.
Interestingly, a similar study found that an increase in gray matter was also found for those whose second language was not a spoken one, such as American Sign Language.
Further support for the benefits of bilingualism is found in PET scans which measured metabolism of glucose in the brain. The scans demonstrated a significant difference in those who spoke more than one language. The ability of the brain to metabolize glucose (sugars) is strongly tied to brain function, so much so that Alzheimer's has been nicknamed Type 3 Diabetes.
Finally, the brain may process tasks differently if the person is bilingual or monolingual. Some research has shown that in bilinguals, the brain is more efficient at processing tasks and better able to ignore distractions when doing so.
While any amount of learning is beneficial, it's unlikely that a brief exposure to a second language actually helps lower your dementia risk. Rather, those who learned the second language earlier in life and those who use more than one language regularly seem to have the greatest likelihood of cognitive benefit.
A high level of proficiency in both languages also appears to be important. In other words, knowing just a few phrases is unlikely to reduce your dementia risk, while being competent to serve as a translator is more apt to provide brain benefits.
While these studies seem to consistently point to a strong connection between bilingualism and a reduced dementia risk, others have questioned the cause of this correlation.
For example, researcher Esme Fuller-Thomson attribute lower rates of dementia in bilinguals to a phenomenon called the "healthy migrant" effect. By this, she means that the lower dementia risk may not be due to the bilingual factor but instead may be related to the healthiness and resiliency needed for people to emigrate to a new country. Thus, she asserts that factors such as good overall health may be responsible for the lower risk of dementia, as opposed to the knowledge and use of another language.
Other researchers have identified another factor that could contribute to a correlation between bilingualism and a decreased risk of dementia—the higher education level that is present in some people who speak more than one language.
This question of correlation versus causation is a common one in the field of science, and it's difficult to pull apart the many factors that could be affecting the results in these studies that show a correlation between improved brain functioning and bilingualism.