Alex, 33, said that his sister's long battle with bulimia left her weak and more susceptible, reported Guardian online.
"She would have died eventually, the way she was going, but what really killed her was the bulimia", Alex said.
According to her brother, who was speaking to mark the opening of an exhibition dedicated to his sister's life in north London, her system had been fatally weakened by years of bulimia, a disease in which bouts of extreme overeating are followed by depression and self-induced vomiting.
Alex also revealed that Winehouse had developed bulimia in her late teens and had never shaken off the illness.
"My sister had a group of friends who were all doing it. They'd put loads of rich sauces on their food, scarf it down and throw it up.
"They stopped doing it, but Amy never really stopped. We all knew she was doing it but it's almost impossible to tackle, especially if you're not talking about it," he added.
Winehouse, won five Grammy awards for her 'Back to Black' album, died in July 2011 at the age of 27.
