A Healthy Poke: Demystifying the Science Behind Acupuncture

(Extraído de The Atlantic.com)

By Alice G. Walton

Sep 29 2011, 10:07 AM ET 14

Many of us have started to embrace the use of alternative medicine, but acupuncture, with its qi, yin, and meridians, still raises eyebrows

While many practices in alternative medicine are slowly but surely making their way into the mainstream, acupuncture is one that still produces skeptical eyebrow raises. This phenomenon is partly due to linguistics. Scientists have worked to elucidate the mechanisms by which yoga, meditation, and various dietary interventions may work on the cells of the body, but there is something fundamentally more ancient-feeling about the language of acupuncture. Go to the NIH's website on complementary and alternative medicine (NCCAM), and even here you'll find a discussion that involves qi, yin, yang, and meridians.

Acupuncture is a "retrospective science, going on for 3,000 years. We know it works, we just don't know why."

Is it possible to discuss acupuncture in a way that makes sense to even the most Westernized brains? The short answer is yes -- but with the caveat there there is no single unifying explanation for how it works. While acupuncture has been demonstrated to be useful in pain management and in treating the nausea and vomiting associated with chemotherapy, other uses have had more mixed results when studied scientifically.

Dr. Leena Mathew is an attending physician in Anesthesiology and Pain Medicine at New York Presbyterian Hospital/Columbia University Medical Center. She uses acupuncture as an "adjunct analgesic modality," meaning that she uses it as a complementary treatment for pain in her patients should they require or prefer it. She and Dr. Josephine Briggs, director of NCCAM, discussed with us the most likely theories of the mechanisms behind acupuncture.

For pain management, one idea is that acupuncture may be working via the gate control theory, first outlined by Melzack and Wall in the 1960s. This theory suggests that pain is transmitted through small nerve fibers from the skin through the spinal cord and on up to the brain. Also present are larger fibers which normally send inhibitory signals to the small pain fibers, which essentially "gates" or prevents a pain signal from being set off. When a painful stimulus comes in, however, the activity in the small nerve fibers overwhelms the large ones, so inhibition is released and the gates of pain opened. Where does acupuncture come in? Theoretically, the needles are placed in positions to stimulate the large nerve fibers, so that the small -- painful -- ones are inhibited. Mathew says that the same logic theoretically underlies why rubbing your elbow after you bang it helps alleviate the pain: you're stimulating the inhibition that quiets the pain.

Another possibility is that endorphins, the body's famed "feel good" chemicals, are behind the effect of acupuncture on quelling pain. Mathew says that the happy little chemicals are released in response to a range of phenomena -- distress, injury, running long distances, chocolate -- and have the knack for acting like morphine on the body and brain. Studies have tracked levels of these molecules in the blood, and shown that acupuncture is linked to higher levels of beta-endorphin at the same time that patients are reporting decreases in their pain levels. Even more, when you inject people with the anti-morphine drug naloxone, the effects of acupuncture are reduced.

But other theories better explain why acupuncture has been shown to work well on the nausea and vomiting (PDF) associated with chemotherapy. In the 1950s, the nerve reflex theory was proposed, suggesting that the body's periphery (the skin) is connected to the internal organs through a reflex called the viscero-cutaneous reflex. "If you stimulate the periphery with acupuncture needles," explains Mathew, "you can change the blood flow pattern to the stomach and abdomen, which could explain the effect on nausea and vomiting."

Acupuncture may also have an effect on the body's stress response system, otherwise known as the hypothalamus-pituitary-adrenal (HPA) axis, which could be why acupuncture patients report lower stress levels and anxiety after treatment, at least in the short term.

If you were wondering when the word "placebo" was going to enter the discussion, here it is -- but it's not what you think. What researchers now know about the placebo effect is that it isn't some hokey "mind over matter" thing. The response is a robust, demonstrable physiological phenomenon, according to Mathew. When people are being "treated" with placebo, you can actually see the change in blood flow patterns in the cortices of their brains in fMRI. Some people are more responsive to the placebo effect than others, and there is no doubt that some of this effect is going on with acupuncture, and particularly heightened in placebo-sensitive individuals.

Which leads to the final theory about why acupuncture may work on certain conditions. The very presence of human touch may have a lot to do with acupuncture's healing power, Mathew suggests. "This is therapeutic touch," she says. "As Westerners, we're disconnected from this. We don't want to touch patients." But just as a mother calms a child simply through her physical/emotional presence, having another human being exert a well-intentioned touch may, in its simplicity, also do a lot to alleviate pain. This effect may have to do with the alleviation of fear and anxiety, things we know account for a huge portion of our perception of pain.

Briggs adds to this idea by mentioning that some of the effects of acupuncture can also be seen when "sham" treatments like toothpicks are used, which can sometimes have an effect similar to acupuncture. This, she says, "tells us that a very important part of acupuncture's effect is the ritual involved, which includes pressure, reassuring practitioners, and the patient's expectation." In other words, the act of acupuncture itself is at least partially what accounts for its effect.

She adds that we need to start asking different questions about acupuncture, and using different language to discuss is. For example, she says that "meridians were developed by a tradition of people who didn't dissect human body -- meridians are not good a scientific question. But, 'How does the practice change our perception of pain?' is a good question. It's quite plausible that pain pathways are modulated by emotion, pill placebo, etc., so it's not surprising that reassurance of ritual or expectation is at play here. "

As Mathews points out, acupuncture is a "retrospective science, going on for 3,000 years. We know it works, we just don't know why. It's very hard to translate into Western language." Still, it should be possible to do so, and we seem to have made some progress. Hopefully more researchers asking the right questions, and coming up with clever new techniques to address them, will help elucidate the mechanisms and unify the theories.