The Bruno Mars song that caused Mark Ronson to lose his hair

The stress of writing one Bruno Mars song saw Mark Ronson collapse.

Mark Ronson collapsed with the stress of producing Uptown Funk.

The 40-year-old star admits the chart-topping track was written in "literally seconds of inspiration" in Bruno Mars' studio with musician Philip Lawrence and producer Jeff Bhasker, but after six months and 54 different versions, they were struggling to complete the song and the strain of getting it right caused Mark to lose his hair and fall ill.

He said "I was so anxious by this point. I was pretending everything was fine and that I had it in the bag.

"I'd lost an inch off my hairline because I was so worried, and I knew the only thing that was missing was my guitar part.

"Jeff suggested going to a restaurant and then he asked me if I was OK because I looked incredibly white in the face.

"I went to the toilets and just started vomiting, then I collapsed and had to be carried out of the restaurant. And then a couple of weeks later it [the guitar part] just came."

Mark was left devastated when his friend and collaborator Amy Winehouse died from alcohol poisoning in 2011 and he feels "lucky" that he knew her before the "madness" she was surrounded with in her later life.

He told Event magazine: "I miss her. She was a huge part of my life and a huge part of my music.

"She was crazily talented and chaos comes as part of that package. I think I was lucky in that none of that madness had really started when we were together.

"People think of Amy and they think of all the screaming headlines. But we'd record in the studio in New York and then go for walks in Brooklyn or spend two hours on the treadmill.

"We'd just laugh a lot and talk a lot about music.

"There was an effortlessness when she sang and my job as the producer then was just to catch it.

"She knew exactly what she wanted. She knew the sound she wanted to make. Forget everything else - Amy was a one-off singer.

"No one really knew who she was then, it was before the craziness, the drugs and the paparazzi. That's the Amy I remember."

- Bang! Showbiz