Steve Jobs reveals hormone imbalance; will remain CEO

In his letter, Mr Jobs said that recent blood tests confirmed that the hormone imbalance had been "robbing" his body of the proteins it needs to be healthy.

Jobs, who turns 54 in February, said he will undergo a "relatively simple" treatment and will remain in charge of Apple.

I've already begun treatment," Mr Jobs added. "But, 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."

Last month, Apple said Jobs wouldn't deliver the keynote address at the Macworld Expo conference this week in San Francisco.

Apple shares are 3.7 per cent higher in New York at $94.14 this morning.

"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," Mr Jobs said in his letter.