This research should be added to that showing that failure of systems in the body, such as stem cells, is as much a consequence of the overall bodily environment and the biochemical signals it generates as it is damage to the systems specifically: "People with kidney failure may think that they're better off getting a new kidney from a young and spry donor, but a recent study indicates that for those over 39 years old, the age of a live donor - ranging from 18 to 64 years - has an insignificant effect on the long-term health of a transplanted kidney. ... [Researchers] analyzed the survival of kidneys from donors of different age groups that were transplanted into recipients of different age groups. Their study included data from all adult kidney transplants from living donors that were performed in the United States from January 1988 to December 2003, with follow-up through September 2007. With the exception of recipients aged 18 to 39 years, who benefited the most when they received kidneys from donors aged 18 to 39 years, donor age between 18 and 64 years had minimal effect on the survival of transplanted kidneys. ... many patients will likely find that participating in living donor paired exchanges - and possibly receiving a kidney from an older-aged donor - is a better option than continuing to wait for a deceased donor transplant."