Scientists have established that the molecule adenosine is critical to explaining how acupuncture works, and have been able to triple acupuncture's effectiveness as a result.
Adenosine is known for its role in regulating sleep, for its effects on the heart, and for its anti-inflammatory properties. But it also acts as a natural painkiller in the skin, inhibiting nerve signals and easing pain.
The team found that it's also active in deeper tissues affected by acupuncture.
"Acupuncture has been a mainstay of medical treatment in certain parts of the world for 4,000 years, but because it has not been understood completely, many people have remained skeptical," says neuroscientist Dr Maiken Nedergaard of the University of Rochester.
"In this work, we provide information about one physical mechanism through which acupuncture reduces pain in the body," she added.
The team performed acupuncture treatments on mice that had discomfort in one paw. The mice each received a 30-minute acupuncture treatment at a well known acupuncture point near the knee, with very fine needles rotated gently every five minutes - much as is done in standard acupuncture treatments with people.
They found that in mice with normal functioning levels of adenosine, acupuncture reduced discomfort by two-thirds. But in special adenosine receptor knock-out mice, it had no effect.
During and immediately after an acupuncture treatment, the level of adenosine in the tissues near the needles was 24 times greater than before the treatment.
Once the scientists realised what was going oin, they tried out a cancer drug called deoxycoformycin, which makes it harder for tissues to remove adenosine.
The compound boosted the effects of acupuncture treatment dramatically, nearly tripling the accumulation of adenosine in the muscles and more than tripling the length of time the treatment was effective.
"It’s clear that acupuncture may activate a number of different mechanisms,” said Josephine P Briggs, director of the National Center for Complementary and Alternative Medicine at the National Institutes of Health.
"This carefully-performed study identifies adenosine as a new player in the process."