Streep is transformed into the divisive politician in "The Iron Lady," which has its British premiere in London on Wednesday.
The two-time Academy Award winner says the role "was extremely daunting, because I'm from New Jersey."
But she says in an interview that her youthful experience as one of just 60 women among 6,000 students at Dartmouth College helped her understand Thatcher's outsider status.
The film has been criticized by Thatcher's allies for showing the 86-year-old former leader as a frail old woman with dementia.
Streep says "probably the most provocative thing it does is consider that she is human."
