She declined to elaborate on Jobs' condition beyond what the statement says, including whether a hormone imbalance is still thought to be the cause of his weight loss.

Speculation about Jobs' health has dogged him since Apple's Worldwide Developer Conference in June, when many people thought he appeared gaunt. Earlier, in 2004, Jobs revealed he had undergone surgery for pancreatic cancer. When he took time off for surgery to remove that tumor, he also handed over the reins to Cook.

Earlier this month, amid rumors that he may once again be seriously ill, Jobs issued a on Jan. 5 in which he said doctors thought they had found the cause of his weight loss -- "a hormone imbalance that has been 'robbing' me of the proteins my body needs to be healthy. Sophisticated blood tests have confirmed this diagnosis."

Apple's share price tends to rise and fall on speculation about Jobs' health. While many companies have charismatic leaders, Jobs is thought to control even minor decisions at Apple, the company he cofounded in the 1970s and brought back to life after returning to it in the mid-1990s.

Following Wednesday's announcement, Apple's shares were trading about $5.45 lower in the after-hours markets, hovering at around $80 per share.