She has built her fame and considerable fortune by baring her soul to a nation of telly addicts on an almost daily basis. But despite her carefully cultivated "woman of the people" image, Oprah Winfrey takes an exceedingly dim view of any outsiders impertinent enough to wonder what really makes her tick.

That, at least, is the verdict of the celebrity biographer Kitty Kelley, one of the book industry's foremost scandalmongers, who claims the magisterial chat-show host's personal privacy is protected by a brand of media censorship so far reaching that it might have turned Senator McCarthy green with envy.

Ms Kelley, who has previously taken a typewriter-shaped hatchet to the lives of such luminaries as Nancy Reagan, Frank Sinatra, and the British Royal Family, will tomorrow publish an unauthorised biography of Winfrey, which is expected to delve into her abusive childhood and somewhat mysterious sex life.

The eagerly awaited tome will have a print run of 500,000, and sufficient buzz already to be in the top 25 of Amazon's sales charts. Yet in contrast to almost every other biography of Ms Kelley's career (many of which have been number one bestsellers) the launch of Oprah has attracted virtually no interest from major TV channels.

Every US network – with the exception of NBC, which will have her on Monday's Today show – is reported to have decided, after some consideration, not to feature the author in its programmes. The management of ABC allegedly slapped a formal ban on her appearing on its airwaves.

In an interview this week, Kelley blamed the blackballing on a collective paranoia across the industry about upsetting Winfrey, who remains one of the most powerful individuals in broadcasting and exerts a mysterious hold over prominent talk show hosts who have refused to have anything to do with the new book.

"We have already been told by Barbara Walters' producer 'no, you cannot be on The View. I cannot disrupt my relationship with Oprah'," Kelley revealed to The New York Times last week. "Joy Behar, the same thing. Charlie Rose; Larry King said 'I will not do it, it might upset Oprah'. Even David Letterman."

Her disclosure has prompted soul-searching in US media circles, where broadcasters like at least to pay lip service to the notion that powerful individuals cannot exert undue influence on their news agendas. It has also highlighted Winfrey's enduring hold on the levers of power, which was very publicly evident during the rise of Barack Obama, and persists despite her recent announcement that she intends to retire from her chat show next year.

A spokesman for Kelley, who interviewed roughly 850 of the TV presenter's acquaintances during three years of research for the book, said the networks that refused to invite Kelley on air had "cited sensitivity to their relationship with Ms Winfrey".

The TV stations are perhaps right to be cautious: the author is a formidable and very thorough disher of celebrity dirt whose latest biography, according to at least one critical reading, will present Winfrey as "a cold manipulator who requires everyone around her to sign confidentiality agreements". According to some reports, the book will say that Oprah won't even give her phone number to her own mother – she has to ring the star's PA and leave a message.

The book will delve into the tough Mississippi childhood which Winfrey occasionally refers to, but about which she is notoriously sensitive. She was sexually molested and made pregnant at the age of 14, but bore a son who died in infancy. "This book names the boy that she gave birth to, presents the birth certificate and tries to show how these secrets controlled Oprah for most of her life," says Kelley.