The vitaminC@P25TiO₂NPs, on the other side, did not have any effect on cell protection against ROS. This might be due to the fact that vitamin C, a well-known scavenger of ROS, could behave as prooxidant and even promote ROS and lipid peroxidation [39]. It was recently described that at small concentrations of vitamin C, the prooxidant effects dominate; while in large concentrations the antioxidant ones predominate [40]. The effect also depends on the cell state and the interaction of vitamin C with light. In this case, ascorbic acid may act as an antenna to harvest visible light when conjugated to P25TiO₂NPs. Indeed, it was previously found that this combination (in some ratios) could have an improved photocatalytic activity, possibly due to a red shift in its light absorbance [41]. Further studies on vitaminC@P25TiO₂NPs were not conducted, because of the poor antioxidant capacity [42].

It's all over the place in our environment, said Dr. Johnson-Arbor.

Yes. According to the FDA and other regulatory agencies globally, “titanium dioxide may be safely used for coloring foods”. Titanium dioxide is safe to use, and the FDA provides strict guidance on how much can be used in food. The amount of food-grade titanium dioxide that is used is extremely small; the FDA has set a limit of 1 percent titanium dioxide for food. There is currently no indication of a health risk at this level of exposure through the diet.

Permanence and Stability

How we’re exposed to an ingredient matters greatly in terms of our long-term health. 
  
Research shows that inhaling titanium dioxide particles in significant quantities over time can cause adverse health outcomes. Unless you work in an industrial setting, inhaling substantial amounts of titanium dioxide is highly unlikely.