Joint effort: bacteria in yogurt combat arthritis in rats.

Consuming either dairy foods or certain types of bacteria may fight arthritis, research in laboratory rats suggests. Yogurt that contains live bacteria appears to be particularly effective against the inflammatory joint disorder.

Various bacteria, when eaten, combat pathogens in the intestines and bolster a person's immune system. Called probiotics, such bacteria can also provide benefits when introduced into other parts of the body, such as the nose and vagina, to keep harmful bacteria from taking hold (SN: 2/2/02, p. 72). However, researchers have an incomplete understanding of what makes a bacterium act as a probiotic and whether probiotics can be helpful in tissues that don't directly receive them.

To investigate such questions, Abraham Weinberger of the Felsenstein Medical Research Center in Petah Tikva, Israel, and his colleagues injected rats with chemicals that normally cause arthritis within 2 weeks.

Beginning either before or after the injection, the researchers supplemented the rats' normal daily diets with 0.5 milligram of water, pasteurized milk, or yogurt. The yogurt contained live Lactobacillus bulgaricus, which converts milk into yogurt. This microbe is present in U.S. yogurts bearing the words "live and active cultures."

For some rats, the yogurt was supplemented with a live Lactobacillus rhamnosus strain GG (LGG) that has several established probiotic effects. Some other rats received water containing either live or dead LGG.

Rats consuming either type of yogurt starting before the chemical injection experienced no arthritis or developed only mild symptoms that soon disappeared. Those that got water with either live or dead LGG or that drank milk developed stronger symptoms that were nevertheless milder than those of rats that received sterilized water.

The researchers observed similar results when they supplemented the rats' diets after the chemical injection but before the appearance of arthritic symptoms.

In rats whose diets changed after arthritis appeared, only the water containing live LGG and the two yogurts mitigated symptoms, the researchers report in the August Journal of Nutrition.

"The study is encouraging from several points of view," says physiologist Osmo Hanninen of the University of Kuopio in Finland. For one thing, he says, Lactobacillus species, called lactobacilli, thrive in yogurt, and the medium apparently enhances their probiotic effects. Also, since yogurt's natural bacteria seem to produce much of the benefits of LGG, adding LGG during manufacture may be unnecessary for endowing yogurt with probiotic properties.

"I don't know if I'd pay more money for LGG," says Gary W. Elmer of the University of Washington in Seattle. "But I would certainly consume a yogurt that contained a live lactobacillus, which I do."

Lactobacilli produce compounds that act as natural antibiotics. Those compounds neutralize intestinal bacteria that might otherwise provoke an immune attack on joints or other body tissues, some researchers hypothesize. In that context, Hanninen says, the residual presence of natural antibiotics could explain why rats get some benefit from consuming LGG that are already dead.

Alternatively, the infusion of new bacteria into the gut may temporarily distract the immune system from attacking the joints but not permanently improve arthritis, says government immunologist James Chin of New South Wales Agriculture in Camden, Australia. He faults the Israeli researchers for not including sterilized yogurt in their experiments, which could have revealed any benefits of eating the food that are independent of the live bacteria it contains.