Scientists say they have confirmed what grandmothers have known for centuries -- that chicken soup is good for colds.
Chicken soup -- as made by grandma -- contains several ingredients that affect the body's immune system, a team at the University of Nebraska Medical Center found.

Specifically, it has anti-inflammatory properties that could explain why it soothes sore throats and eases the misery of colds and flu, Dr. Stephen Rennard and colleagues said Monday.

"Chicken soup may contain a number of substances with beneficial medicinal activity," the researchers wrote in their report, published in the journal Chest.

"My wife was making chicken soup one year for the Jewish holidays and we were talking about its effects on colds," Rennard, a specialist in pulmonary medicine, said in a telephone interview.

"I said 'well, maybe it has some anti-inflammatory effect,' and she said 'really?' and I said 'why not?' and I said maybe we could find out in the lab."

As it turned out, Rennard's lab was well-suited to making such tests. "In the lab we study inflammation and injury and repair mechanisms in the lung as related to asthma and emphysema and so on," he said.

So Rennard's wife Barbara Rennard made up a batch of her grandmother's chicken soup, which includes chicken, onions, sweet potato, parsnips, turnips, carrots, celery stems, and parsley. Rennard said his wife added no salt but did include matzo balls, a kind of dumpling.

Then they ran laboratory tests. Not only did they test the soup as a whole, but they separated out the components.

"These tests were in the laboratory and it doesn't test (chicken soup) clinically in colds," Rennard stressed.

Neutrophil movement stopped

They found that chicken soup and many of its ingredients helped stop the movement of neutrophils -- white blood cells that eat up bacteria and cellular debris and which are released in great numbers by viral infections like colds.

Neutrophil activity can stimulate the release of mucous, which may be the cause of the coughs and stuffy nose caused by upper respiratory infections such as colds.

"All the ingredients were found to be inhibitory, including the boiled extract of chicken alone," they wrote.

Rennard said vitamins and other agents in the ingredients could, plausibly, have biological action.

The researchers also went to the store and bought 13 different commercial brands of soup to test.

"About a third of them were more active than grandma's soup," Rennard said, adding that he could not remember which kinds of soup they were.

"One or two of them had very little activity at all. Vegetarian vegetable soup had some activity."

To be safe, they also tested plain Omaha tap water which, to their relief, had no effect. "If tap water were active, that would be disturbing in a number of ways," Rennard said.

Some researchers have suggested in the past that perhaps the steam from the soup, or the chicken fat, may play a role in soothing inflamed airways. Rennard said this was possible.

He also said there could be a "TLC" (tender, loving care) factor. "If you know somebody prepared soup for you by hand, that might have an effect," he said.

Rennard said he had no immediate plans to test chicken soup any further. "I have no doubt that generations from now, people will read this and the only thing of interest will be the recipe," he said.

"It really is good soup."