Learning languages protects against Alzeimer's

It won't stop you getting it, as that depends on many other factors, but being bilingual slows down the process and lessens the effects: http://news.nationalgeographic.com/news/2011/02/100218-bilingual-brains-alzheimers-dementia-science-aging/?source=link_fb20110221alzeinerslanguages

The basic idea is that a bilingual brain is better equipped to cope with the decline in cognitive functions caused by the disease.

But then my question is: does speaking/learning MORE languages protect MORE? I haven't found the answer to that yet. It would make sense, wouldn't it? Apart from being a convincing argument to take up English (for example) at any age, in spite of already being bilingual in Spanish and Catalan.

If anyone knows any more about this subject, please enlighten us.