For centuries, people have dreamed of drinking from the fountain of youth, a legendary spring that supposedly turns back the clock for those who ingest its waters. No such fountain exists in reality, of course, but some scientists believe they may be a little closer to learning how to slow the aging process and increase lifespan thanks to several studies they're conducting.

First discovered in the earth of Easter Island in the 1970s, the drug rapamycin was first utilized in transplant patients to suppress their immune systems and avoid organ rejection. In subsequent studies, researchers realized that rapamycin lengthened the lives of middle-aged mice by 28 percent to 38 percent. In a follow-up study, rapamycin was added to the diets of middle-aged mice, and their lifespan was extended significantly. Will rapamycin have the same effect on humans that it has on mice? It's too soon to tell, but scientists are hopeful that the drug will at least highlight molecular pathways that they can focus on in future work.

It's been known to scientists for some time that certain proteins called sirtuins can affect lifespan, primarily because sirtuins mimic the effects of caloric restriction. Mice put on a significantly restricted diet live longer than mice that eat all they wish, with reduced levels of many diseases.