The singer-songwriter, whose debut album was the best-sellling record in the UK last year, said her shyness meant she was a loner at school.
Talking about growing up in Alford, Aberdeenshire, she said: "I found it very difficult socially at school to meet people, to make friends and for people to understand me. I felt very different, so I spent most of the time writing music by myself."
Sande's family moved to Alford when she was four. "There was a lot of responsibility on me as the eldest... and being mixed race," she said. "The only mixed-race family in the village. It made me quite serious."
Sande sold 1.4 million albums last year and performed at the opening and closing ceremonies of the Olympics.
She says her teenage loneliness may have helped lead her to where she is now. "If you don't fit in, there are no rules. You can do what you want."