New York: Chronic exposure to a common food additive found in everything from chewing gum to bread can decrease the ability of small intestine cells to absorb nutrients and act as a barrier to pathogens, warns a study.

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Ingestion of the compound, known as titanium dioxide, is nearly unavoidable. It can enter the digestive system through toothpastes, as titanium dioxide is used to create abrasion needed for cleaning. The oxide is also used in some chocolates to give it a smooth texture.

"Titanium oxide is a common food additive and people have been eating a lot of it for a long time -- don't worry, it won't kill you! -- but we were interested in some of the subtle effects, and we think people should know about them," said one of the authors of the study, Gretchen Mahler, Assistant Professor at Binghamton University, State University of New York.

For the study, the researchers exposed a small intestinal cell culture model to the physiological equivalent of a meal's worth of titanium oxide nanoparticles -- 30 nanometers across -- over four hours (acute exposure), or three meal's worth over five days.

Acute exposures did not have much effect, but chronic exposure diminished the absorptive projections on the surface of intestinal cells called microvilli, showed the findings published in the journal NanoImpact.

With fewer microvilli, the intestinal barrier was weakened, metabolism slowed and some nutrients -- iron, zinc, and fatty acids, specifically -- were more difficult to absorb. 

Enzyme functions were negatively affected, while inflammation signals increased, the study said.

"To avoid foods rich in titanium oxide nanoparticles you should avoid processed foods, and especially candy. That is where you see a lot of nanoparticles," Mahler said.