Does a good massage do more than just relax your muscles? To find out, researchers at Cedars-Sinai Medical Center in Los Angeles recruited 53 healthy adults and randomly assigned 29 of them to a 45-minute session of deep-tissue Swedish massage and the other 24 to a session of light massage.

All of the subjects were fitted with intravenous catheters so blood samples could be taken immediately before the massage and up to an hour afterward.

To their surprise, the researchers, sponsored by the National Center for Complementary and Alternative Medicine, a division of the National Institutes of Health, found that a single session of massage caused biological changes.

Volunteers who received Swedish massage experienced significant decreases in levels of the stress hormone cortisol in blood and saliva, and in arginine vasopressin, a hormone that can lead to increases in cortisol. They also had increases in the number of lymphocytes, white blood cells that are part of the immune system.