The founder and chief executive of Apple computers Steve Jobs, a survivor of pancreatic cancer, said today that a hormone imbalance was to blame for the weight loss that has prompted worries about his health.
Mr Jobs (53) said he will undergo a "relatively simple" treatment and will remain in charge of Apple.
"A hormone imbalance ... has been 'robbing' me of the proteins my body needs to be healthy," Jobs said in a public letter, adding, "Sophisticated blood tests have confirmed this diagnosis."
Speculation about his health persisted in 2008 as a gaunt-looking Mr Jobs appeared public events. Those worries intensified after the California-based company said last month that Jobs would not be making his annual key address tomorrow in San Francisco at the Macworld conference.
Officially Apple said Mr Jobs would not take the stage because this year will mark the company's last appearance at the show, which is run by a separate company, the IDG technology media group.
While some analysts expected this week's Macworld to help Apple show it could execute its long-term strategy without Jobs as its public face, others have questioned the company's viability without Jobs, who has emphasised the design principles that made favourites out of Apple's Mac computers, iPods and iPhones.
Today's announcement is not likely to end the speculation, unless Apple offers more details on Mr Jobs' condition
In his letter he said, "I will be the first one to step up and tell our board of directors if I can no longer continue to fulfil my duties as Apple's CEO."
Jobs offered few details on his diagnosis, however.
"The remedy for this nutritional problem is relatively simple and straightforward, and I've already begun treatment," he said. "Just like I didn't lose this much weight and body mass in a week or a month, my doctors expect it will take me until late this spring to regain it."
Jobs announced in 2004 that he had undergone successful surgery to treat a form of pancreatic cancer.