In Health Watch:About 5 million Americans have Alzheimer's.Catching the disease in the initial stages is difficult but researchers may have found an interesting clue.Manuel Gallegus reports.Diagnosing Alzheimer's early is difficult and doctors often don't catch the disease until patients show significant memory problems.But researchers may have discovered an early indicator - rapid weight loss.Dr. Michael Freedman says, 'Weight loss it's turning out is a very important sign.'In a new study scientists followed 18-hundred seniors and found that people wholost weight quickly, and weren't trying to, were three times more likely to develop dementia... a precursor to Alzheimer's.An unexplainable drop in weight during older age can be caused by many conditions.... including diabetes or cancer. Now doctors are starting to put dementia and Alzheimer's on that list of possibilities.Doctors say dementia patients often lose their appetite.Dr. Freedman says, 'The part of the brain that gives us an appetite has been destroyed - so the chemicals that make us hungry are no longer being produced therefore the person will just stop eating.'Physicians say this latest finding gives them an additional clue in diagnosing the disease.Dr. David Langer says, 'if I'm a specialist I might be more likely to ask have they had recent weight loss or weight loss out of proportion to what they normally expect.'Experts hope that by looking further into how Alzheimer's effects the parts of the brain that deal with hunger and weight .. they'll get a better overall understanding of the disease.Manuel Gallegus, CBS News, Los Angeles.