Apple fans and the tech community responded in shock today following the announcement that Steve Jobs, chief executive of Apple, was stepping down from his role while he fights a "hormone imbalance" that has made him lose weight rapidly.

In a letter to employees last night, Mr Jobs announced he was taking a five-month medical leave of absence until the summer, saying that his health issues "are more complex than I originally thought".

Bloggers, Macolytes and analysts lined up to express their surprise at the news, and said they were concerned about the long-term future of the company.

Dan Frommer from the respected tech blog, Silicon Valley Insider, said: “Apple will gradually lose its lead - especially if it doesn't quickly put in place a plan to move forward without Steve

“Pundits will argue all day that Apple is more than Steve Jobs. Fine. But Steve Jobs is Apple. He might not write code or sit in chip fabs. But he makes the big, important decisions that make Apple products Apple products. New decision-makers will make choices Steve wouldn't make. Talent will leave. Etc.”

Mr Jobs is seen as crucial to the company and the driving force behind iconic products such as iTunes, the iPod and the iPhone.

While the majority of opinion suggested Mr Jobs departure was a serious, if not fatal, blow to the company, others argued that the culture Mr Jobs had created means the company is likely to remain strong without him.

In a post entitled, “Why Steve Jobs’ leave of absence from Apple won’t matter - but everyone will think it will,” the hugely influential TechCrunch blog wrote:

“Steve Jobs has imbued his company with so much of himself and his ideas that, like the movie, he has created a veritable army of Spartacus’s. They know what to do. Apple already has amazing momentum, especially with the iPhone”

Speculation was rife yesterday about the cause of the “hormone imbalance” which Mr Jobs said earlier this month was “"robbing me of the proteins my body needs to be healthy".

Yesterday, in an email to staff, he said he would take the leave of absence "in order to take myself out of the limelight and focus on my health, and to allow everyone at Apple to focus on delivering extraordinary products".

Doctors said that, given the length of time Mr Jobs is planning to take off, he could be facing surgery to remove his pancreas.

Mr Jobs had an similar to a “Whipple” procedure, which involves removing parts of the pancreas, bile duct and small intestine, after he was diagnosed with a rare type of pancreatic cancer in 2004.

Doctors said that a potential side effect of this procedure is that the organ has to be removed to prevent pancreatic leak, and the patient has to be kept alive with insulin to regulate blood sugar.

Yesterday, shares were temporarily suspended before the announcement. When they reopened, the news of his poor health sent Apple stock spiralling down nearly 10 per cent to $77 in after-hours trading, their lowest level since December 2006.

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