Bilingualism, Trilingualism and Multilingualism

I am all involved in this subject, researching for my Final Project in TEFL.
Mainly I came to different conclusions:
- it is valuable to be bi/tri/multilingual.
- researchers suggests that bilingualism may delay the onset of age-related dementia, including Alzheimer’s disease, by up to four years. Although scientists don’t know why bilingualism creates this “cognitive reserve,” some theorize that speaking two languages may increase blood and oxygen flow to the brain and keep nerve connections healthy—factors thought to help ward off dementia.
- bilingualism is extremely widespread and is the norm in today's world.

More recently, scientists have discovered that bilingual adults have denser gray matter (brain tissue packed with information-processing nerve cells and fibers), especially in the brain’s left hemisphere, where most language and communication skills are controlled. The effect is strongest in people who learned a second language before the age of five and in those who are most proficient at their second language. This finding suggests that being bilingual from an early age significantly alters the brain’s structure.
 Research_On_TheBilingualbrain