The micro-blogging site has grown by 1,382 per cent since last year, from 475,000 unique visitors in February 2008 to seven million in February 2009.
The Nielsen data shows that the majority of Twitter users are not teenagers or college students, as on many other social networking sites, but are from older generations.
Some 42 per cent of the site's users in February this year were aged between 35 and 49, while 20 per cent were between 25 and 34.
Nielsen also found that 62 per cent of Twitter users visit the site while at work, and 35 per cent from home.
The ability for users to access Twitter from a mobile phone is "a driving factor in the social network's success", according to Nielsen. In January this year, 735,000 unique visitors accessed the Twitter site through their mobile.
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