The Olympic champion figure skater, who joined the ITV1 show this year, was tracked by the communist regime for 17 years to ensure she didn't defect to the West, The Mirror reports.
"I discovered the Stasi had me in their sights when I was an 8-year-old figure-skating student. I had been watched over my entire life - observed, spied upon, manipulated. When I eventually got hold of my Stasi file there were 3,000 pages, in 27 boxes. I was shocked and horrified by the extent of it," she said.
"I went through all kinds of emotions - anger, disbelief, laughter at the absurdity of it. You think, 'Oh my God - how can somebody spy on your life when you're only eight years old? OK, by 19 I was an Olympic champion and the whole world knew me, so the government was afraid that I'd defect and damage the standing of the country.
"I could see why they might have been spying on me then, but not when I was a child. The files were as intimate as diaries, but also full of made up stories about me."
The Stasi are said to have bugged Witt's flat and gathered information on her health, friendships and relationship with former trainer Jutta Muller, even recording the exact times of her sexual encounters.
Witt added: "People were coming out of the woodwork and telling lies about my past. I couldn't begin to deal with all of that in interviews. I needed to write the book and address it all.
"It felt ridiculous to be writing my own biography at 27 instead of 60 or 70, but I was forced to do it just to keep the facts straight."