Parents concerned about their children’s ability to ward off colds and flu might want to feed them a spoonful of bacteria.

A study published in the August edition of the medical journal Pediatrics suggests that probiotics, the healthy bacteria found in yogurts, reduced the incidence and duration of cold and flu symptoms in children ages 3 to 5.

The study used supplements of lactobacillus acidophilus alone or in combination with bifidobacterium animalis, both of which can be found in commercially available yogurts. The children took the supplements twice a day for six months.

Compared with a placebo group, the single probiotic reduced incidence of fever by 53 percent, cough by 41 percent and runny nose by 28 percent. The combination treatment reduced fever by 73 percent, coughing by 62 percent and runny nose by 58 percent.

Duration of symptoms was cut by a third in kids taking the single probiotic and in half by kids taking the combination.

The probiotics also substantially reduced the amount of antibiotics prescribed to kids and the number of days of school missed.

The study did not test whether probiotics could be given after a child becomes sick to limit the illness. The research was funded by Danisco, a probiotic supplement manufacturer.

On the one hand, such affiliations are thought to undermine the validity of research finding. But the double-blind, placebo-controlled study was sufficiently well-designed to be included in a mainstream medical journal.

The doses taken by the children were roughly equivalent to the amount of probiotics in an 8-ounce serving of yogurt. And the study found no adverse effects of probiotics on the children.

A 2005 study conducted in Germany found a similar effect when asking 475 men and women to take a probiotic and a multivitamin for 5 1/2 months.

The treatment reduced respiratory infections by 13 percent and flu symptoms by 25 percent and cut the number of days with a fever in half.

Immune response tests showed a significantly higher response in those taking the supplements than in those in the placebo group.

Probiotic-containing yogurts have been studied for a variety of health conditions and have shown promise in reducing the likelihood of diarrhea after taking antibiotics. Antibiotics often kill the healthy bacteria needed for digestion, leading to gastric issues. Yogurts with probiotics can replenish some of the bacteria and restore healthy digestion.

But clinicians caution that not all probiotics are created equal. Probiotics are highly specific in function, and benefits attributed to one type of probiotic might not be shared by other types of probiotics.

The American Gastroenterological Association maintains that while probiotics are considered safe for the general public, more research is needed to establish a definitive benefit.

“In some respects, the industry has grown faster than the research, and scientists and doctors are calling for more studies to help determine which probiotics are beneficial and which might be a waste of money,” the group said in a statement about probiotics on its Web site

Yogurt-giant Dannon Co. recently settled a lawsuit regarding claims that its Activia and Dan-Active yogurt products boosted immunity or that they aided in digestion. The suit claims that Dannon had no evidence that its yogurt was any more beneficial — and worth the 30 percent higher cost — than other types of yogurt.

Andrea Garen, a registered dietitian working for the Dairy Council of California, suggested foods such as yogurt, garlic, citrus fruits and chicken could help boost the body’s immune system. There’s little hard evidence to support that, but nutrition experts maintain there’s little downside in eating those foods.

“It’s important to eat a variety of healthy foods from all food groups throughout the year,” Garen said. “But it’s particularly significant during flu season.”