No company relies more on its CEO than Apple does on Steve Jobs, so when word got out that the man behind the iPhone, already dogged by speculation regarding his visibly poor health, was skipping out on his annual appearance at the Macworld Expo, investors were understandably jittery—maybe even panicked.

Observers had long suggested that Jobs, a survivor of pancreatic cancer, come clean with whatever was ailing him in order to reassure his shareholders that their money was in stable hands. The vacuum of information had led to mass sell offs of Apple stock over unsubstantiated rumors several times, including a 2 percent drop just last week. The notoriously secretive Jobs finally tossed his shareholders a bone yesterday when he released a letter confessing to a “hormone imbalance” for which he was receiving treatment.

Of course, it could just be that the years are catching up on the overworked Jobs, who turns 54 in February.

“I've decided to share something very personal with the Apple community so that we can all relax and enjoy the show tomorrow,” Jobs wrote. “As many of you know, I have been losing weight throughout 2008. The reason has been a mystery to me and my doctors. A few weeks ago, I decided that getting to the root cause of this and reversing it needed to become my #1 priority. Fortunately, after further testing, my doctors think they have found the cause—a hormone imbalance that has been 'robbing' me of the proteins my body needs to be healthy.”

With virtually no additional details regarding this newly disclosed illness, some critics were skeptical that Jobs's condition was as simple as he made out. To understand more about Jobs's purported condition, I talked to an expert in male hormone imbalances—Dr. John Morley, geriatrician and endocrinologist at St. Louis University Medical School.

According to Morley, Jobs' visible symptoms of weight loss and anemia are consistent with a variety of hormone disorders known as “polyglandular failure syndromes” that can cause a range of nutritional problems for patients. “I would think he fits into that spectrum,” Morley said. “He most probably has B12 deficiency.”

B12 deficiency is associated with nausea, diarrhea, and paleness, all of which could apply to the gaunt Jobs. Other disorders that might be behind Jobs's illness include adrenal disease, which afflicted John F. Kennedy and can cause weight loss and diarrhea; and celiac disease, which renders people unable to digest wheat and causes malnutrition.

Despite speculation that surgery on Jobs's pancreas in 2004 to remove a tumor could be behind his current condition, Morley said that a damaged pancreas might lead to diabetes and enzyme deficiencies consistent with Jobs' condition, but would likely not affect hormones. So—if Jobs's story is to be believed—his hormone imbalance is probably unrelated.

Jobs wrote that his nutritional problem was “relatively simple and straightforward” and that he expected to regain his old weight by late spring, an analysis Morley said was consistent with hormone imbalance. “All of these are easily treatable either with dietary manipulation or taking a tablet each day,” he said. “For adrenal disease, you give steroids, for B12 you give back B12, for celiac disease you cut the things that are causing the problem out of your diet.”

Of course, it could just be that the years are catching up on the overworked Jobs, who turns 54 in February. “The alternative is he's just getting old, his male hormone is getting down,” Morley said. “But that won’t give you diarrhea, so he probably would have something along with it. I think most likely he fits somewhere into the cluster of endocrine disorders.”

For their part, investors appear satisfied with Jobs's explanation for his ill health: Apple stock rose 4.2 percent yesterday after news of his condition was reported by the Wall Street Journal.

Benjamin Sarlin is a reporter for The Daily Beast. He previously covered New York City politics for The New York Sun and has worked for talkingpointsmemo.com.