Jobs is handing the day-to-day running of the business to Apple's chief operating officer Tim Cook but said he will remain involved in "major strategic decisions" during his rest.
Jobs broke his silence on the subject of his health ten days ago, revealing he was suffering from a "hormone imbalance" but he would stay at work and expected to return to full health by spring.
He has now emailed Apple employees to confide that he has learned his health issues are "more complex" than he originally thought.
Investors, who have been worried both by Jobs' condition and by being kept in the dark about it, may decide to sue Apple over its lack of disclosure according to US reports.
The news from Apple sent the company's shares down as much as 11% in extended trading yesterday on the Nasdaq market.
One strand of speculation about Jobs' health links to the pancreatic cancer he was treated for in 2004.