FAYETTEVILLE, Ark. — When sneezing and a prickly throat signal an oncoming cold, many people reach for what they believe will be a safe preventative — a tea or capsule containing echinacea. In the first study to examine the effects of a botanical supplement on bacteria in the gastrointestinal tract, research at the University of Arkansas suggests people may be risking some unwelcome side effects with this common herbal remedy.

Although various botanical extracts have been shown in the laboratory to have some antimicrobial effects, previous to this research there had been no published information about their effect in vivo — in the human gastrointestinal tract. Research conducted by Jerald C. Foote, assistant professor of food and human nutrition, and graduate student Laura Hill yielded some surprising results and pointed to the need for further research.

The researchers worked with 15 healthy adults who took daily doses for 10 days of a supplement that offered a consistent amount of Echinacea purpurea, one of the commonly used varieties of Echinacea. The participants recorded any adverse effects, which proved to be minor. Stool specimens were collected and tested prior to using echinacea and again 10 days and 17 or 18 days following the supplementation.

Although the researchers had expected to see no result from the echinacea, they found that gastrointestinal bacterial counts increased for three groups of organisms during supplementation. Concentrations were increased for the total group of aerobic bacteria, and for the anaerobic Bacteroides in general and Bacteroides fragilis in particular. Anaerobic bacteria — those that grow where there is no oxygen — comprise the majority of the bacteria in the human colon. While Bacteroides are an important feature in the normal life of the colon, under certain conditions they also can act as pathogens, especially strains of B. fragilis.

Foote and Hill pointed out that increased Bacteroides concentrations have been reported in people at high risk for colon cancer. Studies have shown that a specific strain of B. fragilis may contribute to inflammatory bowel disease and diarrhea.

The UA researchers noted that their study showed a significant increase in bacteria after only 10 days. They pointed out that the German Commission E, a body that sets guidelines for use of herbal products in Germany, suggests that echinacea can be used for up to eight weeks. In light of their research, Foote and Hill caution that “prolonged consumption could prove deleterious” to bacteria in the gastrointestinal tract, particularly for those who are ill.

Their research, they conclude, shows that larger studies are needed to target the specific bacteria affected and to determine whether particular components or the combination of components in echinacea affect bacteria in the human gastrointestinal tract.

The report on the results of their research, “Echinacea purpurea Supplementation Stimulates Select Groups of Human Gastrointestinal Tract Microbiota,” was published in the Journal of Clinical Pharmacy and Therapeutics. In addition to Foote and Hill of the Dale Bumpers College of Agricultural, Food and Life Sciences, coauthors were C.E. Cerniglia and B.D. Erickson of the National Center for Toxicological Research, Food and Drug Administration; and G.S. Denny of the UA College of Education and Health Professions.