Near 50% of food consumers use some dietary supplements, particularly multivitamin (multivitamins). But not as many may pay attention to what such a vitamin supplement is made of. One ingredient often seen in vitamin supplements is zinc oxide as a source of zinc. Supplement formulators use zinc oxide nanoparticles for so called "controlled release" of zinc.
Zinc oxide are also commonly used in processed foods as a source of supplemental zinc and in sunscreens as a sunlight barrier because sunlight cannot travel to the skin because of a thin layer formed by the nanoparticles.
Unfortunately, studies have found evidence indicating that nanoparticles like zinc oxide can induce genotoxicity and cytotoxicity. In other words, it can cause damage to the genetic material DNA and cells and tissues in many organs.
An animal study recently conducted by researchers in India has again demonstrated that zinc oxide induces genotoxic and cytotoxic effects against macrophages in adult mice. The study shows that mice treated with zinc oxide nanoparticles developed signs of toxicity including "loss in body weight, passive behavior and reduced survival."
At higher doses, zinc oxide nanoparticles not only caused "severe" DNA damage in periphearal blood and bone marrow cells, but inhibited DNA repair mechanism to prevent the injured DNA from being repaired. Injured DNA can lead to mutagenesis and eventually carcinogenesis (cancer development).
The study also reveals that zinc oxide induced "severe" inflammation and damage to the liver, lungs and kidneys. These nanoparticles killed macrophages in a dose-response manner, and "caused severe wounds and inhibited cellular migration" as described in the study report. Zinc oxide causes DNA damage and kills macrophages because it induces oxidative stress or high levels of reactive oxygen species (ROS), which is known to be causes for many chronic diseases such as cardiovascular disease, diabetes mellitus, and cancer.
Good news is, the same authors tested in vivo and in vitro one amino acid called N-acetyl cysteine, which can be purchased as a dietary supplement, and found it significantly reduced the genotoxicity induced by zinc oxide nanoparticles.
Some industrial scientists have been aware of the genetoxicity and cytotoxicity of zinc oxide nanoparticles and they stop using zinc oxide nanoparticles in sunscreens. Instead, they use zinc oxide particles of bigger sizes, which are less effective, in sunscreens. That is why some sunscreens have higher amounts of zinc oxide in such products.
Zinc oxide is not the only ingredient in vitamin formulations that are not health-friendly. Other nanoparticles like titanium dioxide and silicon dioxide (silica) are also commonly used in vitamins. All types of nanoparticles can be toxic as the size and shape of these particles decide its toxicity. Vitacost.com does not use titanium dioxide nanoparticles in its vitamin supplements, but still use silica. (David Liu)
Rashmirekha Patia, Ishani Dasa, Ranjit Kumar Mehtaa, Rojalin Sahub and Avinash Sonawanea, Zinc-oxide nanoparticles exhibit genotoxic, clastogenic, cytotoxic and actin depolymerization effects by inducing oxidative stress responses in macrophages and adult mice, Toxicol. Sci. (2016) doi: 10.1093/toxsci/kfw010, First published online: January 21, 2016
