Adult stem cells are undifferentiated cells that exist throughout the human body. They can divide to replenish dying cells, and also regenerate to repair damaged tissues. An example are olfactory cells in the nasal passages, which replenish to restore the sense of smell after suffering a cold.
Researchers have shown that adult stem cells from one germ layer can may be able to be converted into those of another, making adult stem cells at least as useful for cures as [[embryonic stem cells]] might be. For example, adult stem cells have been able to turn marrow cells into heart muscle and blood vessels in humans.<ref>http://www.usccb.org/prolife/issues/bioethic/fact401.htm</ref>
While the United States has the largest medical research budget in the world, it also has the most politically powerful [[abortion]] industry. The industry favors embryonic stem cell research over adult stem cell research in order to legitimize abortion.<ref>On the issue of fetal research, Planned Parenthood Federation of American President Gloria Feldt wrote, "'''[[Planned Parenthood]] supports research using fetal tissue''' in accordance with legal and ethical guidelines and are deeply concerned about the attempt by some to profit from the humanitarian contributions of courageous women."[http://www.prochoiceactionnetwork-canada.org/prochoicepress/00spring.shtml] (emphasis added)</ref> Hence relatively little research is done on adult stem cells in the United States, and most of the advances are made in traditionally pro-life countries. For example, in the case of a recently successful adult stem cell project for diabetics, "the research was done in Brazil because U.S. doctors were not interested in the approach."<ref>http://www.cnn.com/2007/HEALTH/conditions/04/10/diabetes.experiment.ap/index.html</ref> Brazil is a pro-life country that generally prohibits abortion.<ref>http://www.abortionfacts.com/statistics/world_statistics_brazil.asp</ref>