A key way to avoid dementia may be learning another language.
Neurologists are reporting in the largest study to date on the link between language skills and the brain-destroying disease that people who spoke two languages staved off dementia years longer than people who only spoke one language.
Previous studies suggest having more education or engaging in intellectual activities may reduce likelihood of the disease. This study found even those who couldn't read but spoke two languages fared better than people who only spoke one.
"Our study is the first to report an advantage of speaking two languages in people who are unable to read, suggesting that a person's level of education is not a sufficient explanation for this difference," study author Dr. Suvarna Alladi, a researcher at Nizam's Institute of Medical Sciences in Hyderabad, India, said in a journal news release. "Speaking more than one language is thought to lead to better development of the areas of the brain that handle executive functions and attention tasks, which may help protect from the onset of dementia."
An estimated one in three U.S. seniors are expected to die with dementia. Alzheimer's is the most common form of the disease.
For the study, researchers recruited almost 650 people from India who were an average age of 66 and had already been diagnosed with dementia.
About 390 of them spoke two or more languages, and 14 percent of them couldn't read. Languages in India where the study took place include Telugu, Hindi, Dakkhini and English.
Most of the patients -- 240 -- had Alzheimer's disease, 189 had vascular dementia, 116 had frontotemporal dementia, and 103 had dementia with Lewy bodies and mixed dementia.
Regardless of type, dementia is caused by damage to brain cells, which then interferes with their ability to communicate with each other. That in turn affects thinking, behavior and feelings, according to the Alzheimer's Association.
The researchers found people who spoke two or more languages had a later onset of Alzheimer's, frontotemporal dementia and vascular dementia by an average of about 4.5 years compared to people who spoke only one language.
When comparing only those who were illiterate, researchers found speaking multiple languages staved off dementia by an average of 6 years compared to their monolingual counterparts.
"From this point of view, we can say it's clearly not the case that bilingual correlates with better education," study co-author Dr. Thomas Bak, a lecturer at the University of Edinburgh in the U.K., said to CBSNews.com.
There was no added benefit, however, from speaking more than two languages despite previous research showing this effect.
Other studies, including 2011 Canadian research that also found a 4.5 year dementia delay among bilingual folks -- have shown a connection between speaking multiple languages and dementia protection.
Bak however said that those studies were in Canada and involved people from very different genetic backgrounds or lifestyles who may have grown up with different diets -- all factors that can influence dementia risk. His study, however, is the first to only look at people in the same region, which eliminated the effect of immigration that's seen in the previous papers.
"Taken together, our results offer strong evidence for the protective effect of bilingualism against dementia in a population radically different from populations studied so far regarding their ethnicity, culture, and patterns of language use," the researchers concluded.
The authors speculate their study adds more evidence to the idea that "language switching" boosts brain health. That theory suggests bilingual people constantly need to selectively activate one language and suppress the other, Bak explained. This might lead to improvements in executive function, attention and other cognitive processes.
This might explain why the findings held for multiple types of dementia, according to the researchers, since most manifest as problems with attention and executive function in early stages.
Bak plans to further research whether learning a new language at an older age could also lead to protective benefits. He also will continue to track these study participants to see whether speaking multiple languages could slow dementia progression.
But for now, his study found no downside of speaking multiple languages, so it could be recommended way to stave off the disease, just like completing puzzles or eating healthily. While the participants still ended up getting dementia, that's no reason to discount the importance of having five more quality years of life, he pointed out.
For example, if you had a family history of cancer, wouldn't you want to avoid it as long as possible?
"If I could take a tablet or pill that has no side effects and is free and I would know I would get it five years, I would not even think for a second whether to do it or not," he said.
Dr. Stephen Rao, director of the Schey Center for Cognitive Neuroimaging at the Cleveland Clinic who was not involved in the reserach, said to HealthDay, "This is another thing we can add to the list of mental abilities that seem to preserve brain function despite the fact that the brain may be ravaged by a disease like Alzheimer's disease and other forms of dementia."
The study was published Nov. 6 in Neurology.