Steve Jobs, the chief executive of Apple Inc, said on Monday a hormone imbalance had caused him to lose weight but that he would continue as CEO during his recovery.

The statement sent the company's shares up 3.4 percent.

The statement follows investor concern and rumors after Apple recently announced that Jobs, a cancer survivor, would not give the keynote speech at Macworld, which showcases Apple products, this week.

Jobs said in an open letter he had been losing weight throughout 2008 but his doctors have discovered the cause and he has begun treatment. His doctors expect it will take until late this spring to regain the weight, Jobs said.

Apple said in a separate statement that the CEO has its full support during his recuperation.

"As we have said before, if there ever comes a day when Steve wants to retire or for other reasons cannot continue to fulfill his duties as Apple's CEO, you will know it," Apple said. - Reuters