Counterclockwise by Ellen Langer
I've not read this yet; the situationist blog posted about it, with the interesting notion:
One of the studies Langer conducted with five of her grad students was to assemble a group of elderly, reasonably healthy men who would live for one week in a world where the clock was turned back 20 years to 1959. They lived in an environment where the television only played programs from that time, the radio shouting out tunes and news broadcasts from the same era. Photographs, newspapers and magazines, political discussions, everything was a replica of 1959 in their controlled world. The men were directed to let themselves be just who you were in 1959. We have good reason to believe that if you are successful at this, you will also feel as well as you did in 1959, says Langer in her book.
Langer and her team were right; the mind does indeed have wondrous control over the body. During the week the men became more independent, motivated and engaging. At the conclusion of the week each man had gained an average of three pounds, their memories and hearing had improved and the strength of their grips increased the participants actually got younger.