Dannon Company's Activa yogurt is one of many new products that contain probiotics, or 'friendly bacteria,' which pediatricians say may help certain illnesses in children. (M. Spencer Green/Associated Press)

A leading U.S. medical group says there's some evidence that probiotics, or "good" bacteria, may have limited benefits for certain illnesses in children.

But the group says the science isn't yet strong enough to advocate infant formulas containing probiotics. And probiotics shouldn't be given to children who are seriously ill.

The paper by the American Academy of Pediatrics was published Monday in the journal Pediatrics.

About 500 different bacteria live naturally in a healthy human's intestinal tract, and there's a growing understanding of the role they play in health. For years, companies have been making claims that their probiotic pills, yogurts, milks and juices help digestive health and the immune system.

The new report summarizes findings from high-quality scientific studies on some of the active ingredients in the products. The report says probiotics taken early during diarrhea from a viral infection may shorten the illness in otherwise healthy children.

And probiotics also may prevent diarrhea in children who are taking antibiotics, which can sometimes cause the condition.

On the other hand, more evidence is needed before AAP can recommend probiotics for constipation, irritable bowel syndrome or Crohn disease. And there's not enough evidence for recommending probiotics in pregnant women or infants to prevent eczema or asthma.

Future research may find more benefits, the report says. And "prebiotics," which contain fibre and other nutrients that feed probiotic bacteria, also may someday prove helpful.

One warning: Children with compromised immune systems or who use intravenous catheters should not receive probiotics because serious infections have been reported.

The bacteria in the products are only helpful if they're alive, which isn't always the case.

"Consumers should keep in mind that a large percentage of organisms in a probiotic supplement may die before the product is even purchased and labels can be misleading or incorrect," said Dr. Tod Cooperman, president of ConsumerLab.com, which tests products and reports on their quality.

The company tested probiotic supplements last year. Two children's probiotics contained only seven per cent and 21 per cent of the listed amounts. Cooperman suggested that products be stored in sealed containers out of heat, light and humidity. He said it's best to refrigerate them.