Oprah Winfrey has been forced to defend her show's medical coverage after she came under fire for backing alleged controversial and unproven health practices.

American publication Newsweek took aim at the chatshow legend, suggesting she uses her influence to promote certain health remedies that could be dangerous to viewers.

Subjects discussed on the show that have led to the criticisms include actress Jenny McCarthy insisting vaccinations caused her son's autism, and a segment in which a Winfrey viewer admitted swallowing 60 supplements a day.

But the media mogul, who was listed as the second most powerful celebrity by Forbes magazine, insists she is merely opening topics up for discussion.

She says in a statement, "For 23 years, my show has presented thousands of topics that reflect the human experience, including doctors' medical advice and personal health stories that have prompted conversations between our audience members and their health care providers.

"I trust the viewers, and I know that they are smart and discerning enough to seek out medical opinions to determine what may be best for them."