Can Learning a Second Language Delay Dementia?
Dementia is a syndrome (i.e. a collection of symptoms) that tends to affect those over 65. It is generally described as a global loss of cognitive ability, including language skills, memory, understanding and judgement. It can be a debilitating condition, frightening for both the sufferer and their family, and a growing concern in an aging population. A great deal of scientific effort is going into strategies to prevent the onset of dementia in the elderly.
What did the scientists say?
Previous studies have shown that the onset of dementia caused by Alzheimer’s disease can be delayed by as long as five years by multilingualism (i.e. being fluent in two or more languages). It is believed that the process of learning and using another language boosts the brain’s “cognitive reserve“, acting as a form of “brain training” to stave off the effects of Alzheimer’s disease dementia.
However, dementia is a condition with many subtypes, and before this study it was unclear as to whether learning another language would be beneficial in cases where dementia occurred due to another disease or mechanism. Also, the majority of studies were carried out in immigrant populations, which makes it difficult to tell whether the effect is truly biological, or simply a consequence of being in an environment where few people speak the patient’s native tongue. Also, studying immigrants can bias the sample of patients towards a certain culture or ethnic group.
In this study, the scientists try and circumvent this environmental problem by using Indian test subjects. India is a country of many languages, where locals switch languages mid-conversation; speaking several languages is common even amongst those who cannot read or write! This makes it a valuable region for testing whether dementia is affected by bilingualism, especially as both the multilingual and non-multilingual patients in the sample can be drawn from the same population, and thus cultural and environmental biases can be removed.
The scientists used data from 648 patients in Hyderabad, all of whom were diagnosed with one of the following subtypes of dementia: Alzheimer’s Disease dementia, frontotemporal dementia, vascular dementia, dementia with Lewy bodies, and mixed dementia. Family members of the patients were interviewed to assess how many languages they spoke fluently, and at what age dementia developed. Around 60% of the patients spoke more than one language, and roughly the same proportion of both multilingual and non-multilingual patients eventually developed dementia.
The multilinguals developed dementia at an average age of 65.6 years, compared to 61.1 years for non-multilingual patients. The scientists showed that when controlling for a variety of factors, including urban or rural living, gender, education level, and others, this effect was preserved. In fact, when the scientists considered only illiterate patients, the effect increases – these multilinguals develop dementia around 6 years later than their single language counterparts. However, illiterates constitute 14% of the sample, so this figure is less robust than the others.
Most interestingly, this study is the first to demonstrate delay of frontotemporal and vascular dementia by multilingualism (dementia with Lewy bodies and mixed dementia did show a very small delay, but the effect was not statistically significant). The number of extra languages appears to be inconsequential to the effect.
The scientists do note a few shortcomings of the study. They rely on family members for determining at what age dementia develops, so it is unclear how much uncertainty this produces in the typical number of years delay produced by multilingualism. When the level of this effect appears to be similar to that achievable by drugs, we should be very careful that this effect isn’t overstated, for patients’ sakes. Also, how multilingualism is measured isn’t particularly precise, and it again relies on family member testimony. Precisely how early a patient should learn a language isn’t yet clear from this work, but the authors are keen to explore this question further.
What did the Media Say?
The BBC make it clear that only certain types of dementia are positively affected by a second language. They also note the advantages of this study’s unique sample of patients.
Livescience carry out an interview with Thomas Bak, one of the study’s co-authors. They discuss the applicability of the effect to, for example, United States nationals learning a second language in classes. Like the BBC, they correctly report some of the different subtypes of dementia in the study, but they do not report the lack of effect measured for other subtypes of dementia.
USA Today speak to other research groups interested in the same questions, to obtain perspective on this particular paper.
The Daily Mail’s headline emphasises the effect’s strength compared to drugs, which as I’ve already said we should be a bit more cautious about.
Generally speaking, this story is well reported, and the scientists’ desire to follow up these studies to determine whether these positive effects extend to Western citizens taking language classes is well expressed by most outlets.
Suvarna Alladi, DM, Thomas H. Bak, MD, Vasanta Duggirala, PhD, Bapiraju Surampudi, PhD, Mekala Shailaja, MA, Anuj Kumar Shukla, MPhil, Jaydip Ray Chaudhuri, DM and Subhash Kaul, DM (2013)
. “Bilingualism delays age at onset of dementia, independent of education and immigration status”. Neurology early online view: doi: 10.1212/01.wnl.0000436620.33155.a4