NEW YORK (AP) -- Apple Inc. founder and Chief Executive Steve Jobs, a survivor of pancreatic cancer, said Monday that a hormone imbalance is to blame for the weight loss that has prompted worries about his health.
Jobs, 53, said in a public letter that his thinness had been a mystery even to him and his doctors until a few weeks ago, when "sophisticated blood tests" confirmed that he has "a hormone imbalance that has been 'robbing' me of the proteins my body needs to be healthy."
Jobs said he will undergo a "relatively simple" treatment and will remain in charge of Apple.
Speculation about his health percolated in 2008 as Jobs appeared gaunt. Those worries intensified after Cupertino, Calif.-based Apple said in December that Jobs would not be making his annual keynote address Tuesday at the Macworld conference in San Francisco.
Officially Apple said 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. Rather than have its CEO speak even as it prepared to wind down its participation in Macworld, Apple said Phil Schiller, an Apple marketing executive, would give the company's presentation.
While some analysts expected 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 emphasized the design principles that made standouts out of Apple's Mac computers, iPods and iPhones.
Investors appeared happy to have some clarity on his health. Apple's shares rose $3.23, 3.6 percent, to $93.98 in morning trading.
But Monday's announcement isn't likely to end the speculation, unless Apple offers more details on Jobs' condition, AmTech Research analyst Brian Marshall said. Marshall expects Jobs to step down from the CEO post sometime this year, most likely remaining an adviser to the company.
In his letter Monday, Jobs said, "I will be the first one to step up and tell our board of directors if I can no longer continue to fulfill my duties as Apple's CEO."
Jobs offered few details on his diagnosis, however. It was not clear whether the hormone problem resulted from his treatment for cancer or arose in another way.
"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 added that "now I've said more than I wanted to say, and all that I am going to say, about this."
The company's board released a statement separately, saying, "Apple is very lucky to have Steve as its leader and CEO, and he deserves our complete and unwavering support during his recuperation. He most certainly has that from Apple and its board."
Jobs announced in 2004 that he had undergone successful surgery to treat a form of pancreatic cancer -- an islet cell neuroendocrine tumor. The cancer is extremely rare and easily cured if diagnosed early. Jobs did not have a deadlier and more common form of pancreatic cancer, called adenocarcinoma.