Approximately how many words does the "average" person speak during the course of his or her lifetime?

It's fair to say that the estimates vary widely, and there seems to be a lack of substance behind the numbers that are thrown about. Many of them make a distinction that women use many more words than men. Other variables would include the language spoken and the life expectancy of the speaker.

I have a 1980 first edition of Gyles Brandreth's "The Joy of Lex: How to Have Fun with 860,341,500 Words," in the Introduction of which he explains that "If you are a typical American, by the time you die, you will have uttered a total of not less than 860,341,500 words" -without a citation. I note that the book is still in print, but the subtitle is now "An Amazing And Amusing Z To A And A To Z Of Words." http://books.google.ca/books/about/The_joy_of_lex.html?id=HjI4mAn0QXkC&redir_esc=y, http://www.goodreads.com/book/show/401204.The_Joy_Of_Lex, https://en.wikipedia.org/wiki/Gyles_Brandreth

A British television show on the "Human Footprint" estimates it at 123,205,750 words (life expectancy 78.5 years): http://www.dailymail.co.uk/news/article-450618/Fancy-cuppa-We-drink-74-802-them.html

An excellent examination of the unreliable numbers thrown about on this subject is at http://itre.cis.upenn.edu/~myl/languagelog/archives/003420.html, which includes several other useful links at the bottom.