From the May 11th, 2026 The Morning Newsletter by Sam Sifton of The New York Times:
The idea of a third circulatory system will not come as a surprise to anyone who practices traditional Chinese medicine. “This knowledge is actually quite ancient,” one professor told Cooper. “It’s something that other systems of medicine have been offering for a long time, but they didn’t have microscopes.” Mention the interstitium to an acupuncturist and you might get an eye roll, like, “No kidding.” (Ask me how I know.)
Acupuncture works, of course. The studies are clear. People seek it out for treatment of all sorts of ills, from chronic pain and migraines to anxiety and insomnia. The discovery of the interstitium, Cooper writes, may help us better understand how it works.
Traditional Chinese medicine holds that acupuncture is a way to balance the flow of energy — known as chi — through one of the body’s 12 main meridians. Acupuncturists insert thin needles into specific points along those meridians to enhance the flow of chi.
Those specific acupuncture points are within the same areas of connective tissue where fluid flows through the interstitium, researchers found. And when they injected dye into acupuncture points on the forearms of volunteers, it slowly migrated up the arm along a meridian.
“This pathway doesn’t go in the veins, it doesn’t go superficially,” one researcher said. Instead, he told Cooper, it flows through the interstitium between the muscles: “When I saw that, I said: ‘We’re onto something. This truly has to do with acupuncture.’”
