In 2007, Ellen Bialystok of York University in Toronto and two colleagues went through the files of a memory clinic. They looked at 184 patients with dementia, about half of whom had spoken two languages for most of their lives. The bilingual patients had started showing symptoms about four years later than the monolingual ones.
That finding travelled around the world, and it is still the main reason people ask whether being bilingual protects the brain. The honest answer today: being bilingual does not prevent dementia. Some studies found that bilingual people show symptoms several years later, but studies that follow people forward in time, which is the stronger design, have not found a lower risk. Maybe a delay, no proven protection. The benefits you can count on are other ones.
The studies that found a delay
Bialystok's study, published in Neuropsychologia, had one more interesting detail. For a group of patients followed after diagnosis, the disease progressed at the same speed in both groups. The bilingual patients seemed to show symptoms later, but once symptoms appeared, the course was the same.
In 2013, a much larger study came from Hyderabad, India. Alladi, Bak and colleagues reviewed the records of 648 patients with dementia, 391 of them bilingual, and published the results in Neurology. Bilingual patients developed dementia 4.5 years later on average. The difference appeared in several types of dementia, and also in patients who could not read or write. That last point mattered, because a common explanation for the delay is that bilingual people tend to have more education. Speaking more than two languages gave no extra benefit.
Why other researchers are not convinced
Both studies looked back at clinic records. That kind of study has a weakness. The age when symptoms "start" is often the age when someone first visits a clinic, and that depends partly on family, culture and education. Bilingual and monolingual patients may also differ in ways nobody recorded.
The stronger design is to recruit healthy people, note who is bilingual, and follow them for years to see who develops dementia. In 2017, Mukadam, Sommerlad and Livingston combined such studies in a meta-analysis. Across the forward-looking studies, which included 5,527 bilingual people, bilinguals were no less likely to develop dementia than monolinguals. Most backward-looking studies did show later symptoms in bilinguals, but the authors judged them more open to confounding by education and culture.
A wider debate
The dementia question is part of a larger argument about whether bilingual people have sharper "executive control", the mental skills used to switch tasks and ignore distractions. In 2015, Angela de Bruin and colleagues in Edinburgh looked at conference presentations on this topic from 1999 to 2012 and checked which ones were later published in journals. In their study in Psychological Science, results that fully supported a bilingual advantage were the most likely to be published, and results that challenged it the least likely.
That doesn't prove there is no advantage. It means the published literature probably makes it look stronger than it is. Researchers still disagree, and the journal printed replies from other scientists.
What about learning a language as an adult?
One study speaks directly to adult learners. Thomas Bak and colleagues in Edinburgh studied 853 people who had taken an intelligence test at age 11, in 1947, and tested them again between 2008 and 2010. People who had learned a second language did better than their childhood scores predicted, especially in general intelligence and reading. This included people who learned their second language as adults. The study was published in the Annals of Neurology.
It is an encouraging result, and an observational one. It shows a link, not proof that the language caused the difference.
What this means for you
- Learn a language for reasons that don't depend on this debate. Talking to your partner's family, working abroad, reading a book in the original: these benefits are real and start long before fluency.
- Don't treat a language course as a medical treatment. No study has shown that learning a language prevents dementia.
- Use the language, not just study it. The studies that found delays looked at people who used two languages through their lives, not people who once took a course.
- Start at any age. If there is a cognitive benefit, the Edinburgh study suggests adult learners may share it. If there isn't, you still speak another language.
Qlango is built for the part that is certain: actually learning and keeping a language. Lessons are short, and every finished lesson comes back after one, two, four and eight days and then once more. An AI voice reads every example aloud at a speed you can turn down. Our guide to learning a language as an adult covers the advantages adults bring, and here is how long it takes to learn a language at each level.
The Toronto files raised a hopeful question, and nearly twenty years later science has a careful answer: maybe a few years' delay in symptoms, and no proven protection. That is no reason to learn less. It is a reason to learn for the right ones. If you already speak one foreign language and wonder about a second, read about learning two languages at once.
Frequently asked questions
Does being bilingual prevent dementia?
No study has shown that it prevents dementia. Some clinic-based studies found that bilingual patients developed symptoms about four to four and a half years later. But a 2017 meta-analysis of studies that followed healthy people over time found no lower risk of dementia in bilinguals.
What are the benefits of being bilingual?
The certain benefits are practical: you can talk to more people, read and watch more, travel and work more freely. Cognitive benefits, such as better attention control or a delay in dementia symptoms, are debated, and some of the evidence may be affected by publication bias.
Does learning a language later in life help your brain?
Possibly. An Edinburgh study of 853 people found that those who knew a second language did better on cognitive tests in their seventies than their childhood scores predicted. This included some who learned the language as adults. The study was observational, so it cannot prove the language caused the difference.
Are bilingual people smarter?
There is no good evidence that being bilingual makes people more intelligent. Claims of a general "bilingual advantage" in mental control are contested, and a 2015 study found that positive results were more likely to be published than negative ones.
