Potentially providing more proof that fresh food is best, a revealing study from researchers at Binghamton University has found that zinc oxide nanoparticles, present in the lining of food packaging, could reduce the ability of our intestinal cells to absorb nutrients.
Zinc oxide nanoparticles are used in food packaging for their antimicrobial properties. Generally lining the inside of certain canned goods, these inorganic nanoparticles are traditionally considered to be relatively harmless, but a small body of evidence is beginning to suggest that they may have unforeseen health implications.
Using mass spectrometry, this new study first examined several samples of canned food – corn, tuna, asparagus and chicken – to understand how many zinc oxide nanoparticles were being transferred to the food. In some instances, the study found these foods contained up to one hundred times the recommended daily dietary allowance of zinc.
The study then constructed an in vitro model of the small intestine to observe what effect such volumes of nanoparticles were having on intestinal cells. Unlike prior work in the area, this study wasn't examining high levels of toxicity, but rather the more subtle effects of nanoparticle doses that are closer to actual human exposure levels.
Gretchen Mahler, a corresponding author on the study, suggests the results show that the zinc oxide nanoparticles change the way intestine cells absorb nutrients and express proteins.
"They tend to settle onto the cells representing the gastrointestinal tract and cause remodeling or loss of the microvilli, which are tiny projections on the surface of the intestinal absorptive cells that help to increase the surface area available for absorption," says Mahler. "This loss of surface area tends to result in a decrease in nutrient absorption. Some of the nanoparticles also cause pro-inflammatory signaling at high doses, and this can increase the permeability of the intestinal model. An increase in intestinal permeability is not a good thing – it means that compounds that are not supposed to pass through into the bloodstream might be able to."
It's important to note that these effects have only been demonstrated in cell models and not replicated in human beings at this stage. It is generally believed that zinc oxide nanoparticles, when ingested by humans, are dissolved by stomach acids into the form of ionic zinc. The researchers are currently looking at animal models to see if similar effects from ingesting nanoparticles can be observed.
"It is difficult to say what the long-term effects of nanoparticle ingestion are on human health, especially based on results from a cell culture model," says Mahler. "What I can say is that our model shows that the nanoparticles do have effects on our in vitro model, and that understanding how they affect gut function is an important area of study for consumer safety."
This isn't the first study to raise questions over the human health effects of zinc oxide nanoparticles. Although much research has been done to establish the safety of the nanoparticles in sunscreens, there are still concerns about the effects of nanoparticles when ingested. A 2011 study from scientists in Singapore suggested that zinc nanoparticles could trigger mechanisms in cells that potentially lead to the development of cancer.
The new research was published in the journal Food & Function.
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