It looks like scientists are getting closer to being able to answer fundamental questions regarding the effectiveness of adult stem cells versus embryonic stem cells - and why some adult stem cell treatments work, while others fail. It's still all somewhat confused, however, and there is a fair amount of work still to be done.
There are many different types of adult stem cell. A fair summary of what is known today would be that some adult stem cell types are useful in some therapies, although scientists are not sure how they are producing beneficial effects. Embryonic stem cells have been demonstrated to be useful in all circumstances in which they can be controlled - but getting them to do what you want to do is proving to be a hurdle. In both cases, some tests have shown undesirable side effects resulting from some therapies. Other studies have demonstrated very impressive positive results - including people who would otherwise be dead returning to an active life.
Overall, it is important to remember that stem cell researchers don't have the important answers yet. Amazing progress has been made, but more unbiased research is needed to understand how to best use stem cells to treat many currently incurable age-related conditions: Alzheimer's, nerve damage, Parkinson's, diabetes, bone loss, cancer, and many more.
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