Short-term exposure to the nanoparticles of titanium dioxide (TiO2) appeared to leave no lasting effects. However, long term chronic exposure affected the intestinal surface cells’ ability to absorb nutrients such as iron, zinc and fatty acids.
Enzyme activity also significantly decreased following exposure to TiO2 nanoparticles while inflammatory signals increased.
"Titanium oxide is a common food additive and people have been eating a lot of it for a long time,” said biomedical engineering assistant and study co-author professor Gretchen Mahler.
"Don't worry, it won't kill you!," she added. "But we were interested in some of the subtle effects and we think people should know about them."
While the European Food Safety Authority (EFSA) has stated that TiO2 poses no health concerns, data gaps and limitations have prevented them from setting an acceptable daily limit (ADI).
TiO2 safety has centred on the nanosized particle form of the additive when added to food. However, EFSA was quick to play down any concerns.
“While there are no specific limits on the particle size of titanium dioxide used as a food additive, food-grade titanium dioxide consists mainly of larger granules, with limited nanoparticle content,” it said
It added that food-grade TiO2 was not considered a nanomaterial under current European Commission definition.
However, it acknowledged the additive could contain up to 3.2% nanoparticles (less than 100 nanometres in size) by weight.
Last year EFSA commissioned the Joint Research Centre (JRC), to prepare an inventory of currently used and reasonably foreseen applications of nanomaterials in agriculture and food production.
TiO2 was considered the main type of engineered nanomaterial added to food.
To investigate their short-term effects, researchers from Binghamton University, State University of New York, exposed intestinal cells to a meal's worth of TiO2 nanoparticles (30 nanometres in size) over four hours as a way to measure acute exposure.
The experiment was repeated with the cells being exposed to three meal's worth of nanoparticles over five days as a way to test the effects of chronic exposure.
Exposure to these nanoparticles significantly decreased intestinal barrier function following chronic exposure.
Harmful reactive chemicals containing oxygen increased in number as did proinflammatory signalling and intestinal alkaline phosphatase enzyme activity, which all showed increases in response to nano-TiO2.
The team also found iron, zinc and fatty acid transport were significantly decreased in activity following exposure to TiO2 nanoparticles.
Go easy on the doughnuts
“Nanoparticle exposure induced a decrease in absorptive microvilli in the intestinal epithelial cells,” the researchers explained.
“Nutrient transporter protein gene expression was also altered, suggesting that cells are working to regulate the transport mechanisms disturbed by nanoparticle ingestion.”
TiO2 can enter the digestive system through foods such as chocolate, where it is used to give it a smooth texture.
It can also be used in such foods as doughnuts to provide white colour; and in skimmed milks for a brighter, more opaque appearance which makes the milk more palatable.
In response to pressure from the advocacy group As You Sow, doughnut giant Dunkin' Donuts stopped using powdered sugar with TiO2 nanoparticles in 2015.
"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," Dr Mahler added.
Published online ahead of print: doi.org/10.1016/j.impact.2017.01.002
“Titanium dioxide nanoparticle ingestion alters nutrient absorption in an in vitro model of the small intestine.”
Authors: Zhongyuan Guoa, Nicole Martuccia, Fabiola Moreno-Olivasa, Elad Takob, Gretchen Mahlera