Usher urges Justin Bieber to take care of his voice

R&B star Usher has urged teenage pop sensation Justin Bieber to make sure his voice doesn't change too much as he grows into a man.

The Yeah! hitmaker has been mentoring the 16-year-old since they met in 2008.

And now, Usher has warned the teenager to look after himself.

"We're taking the right steps to make sure that he didn't lose too much (ability to hit high notes). It's all about what you eat and really just taking care of yourself," the Daily Star quoted Usher as telling Access Hollywood.