Credit: Lester Cohen/

How does Cameron Diaz maintain those mile-long legs and billion-dollar grin?

Sex -- and lots of it!

The 37-year-old actress tells British Vogue in its July issue, "I don't want to look 25 again," but acknowledges she looks pretty good.

"The fountain of youth [for me], let's see...I guess it's exercise, healthy diet, lots of water, lots of laughter, lots of sex -- yes, sex, we need that as human beings. It's healthy, it's natural, it's what we are here to do!"

And she says she's resisted plastic surgery -- for now. "Yeah, well, hey. I'm not doing anything right now," she tells the mag. "But we'll see. So far, so good. But I'll never say never to anything."

The Knight and Day star is less forthcoming about her current love life with Yankees slugger Alex Rodriguez. When asked if she's in love, she demurs: "You know what? Yes I am. I'm in love with life."

The actress recently reunited with ex Justin Timberlake to shoot the film Bad Teacher together. Timberlake "plays the substitute teacher I, er, set my sights on," she says.

In the comedy, she plays "a very, very bad gold digger" looking to fund a boob job. "I'm having the best time playing her," she says. Her character "doesn't give a s*** about anyone but herself. I'm sure we'll offend everyone with it, which is great."