The Role of Dietary Titanium Dioxide on the Human Gut Microbiome and Health

The U.S. food supply contains large amounts of the food additive titanium dioxide (TiO2), but its impact on human health is unknown. The widespread use of food-grade TiO2 (E171) includes commonly consumed products, such as sweets, gums, white salad dressings, dairy creamers, pharmaceutical fillers, and toothpaste. Production of TiO2 in the U.S. is expected to increase more than 8.9% from 2016 to 2025. There are major limitations with current estimations of dietary TiO2 intake in humans. Such limitations include assessing TiO2 content solely from white-colored foods and including only foods with TiO¬2 labeled as such on its packaging. Natural food products, however, may also contribute a substantial amount of TiO¬2 to the diet. There is also a large variation in the estimated ingestion of TiO2 between studies which is likely due to differences in populations and varying food supplies, variability in analytical method used for measuring TiO2, and absence of validated dietary estimation tools to measure oral TiO2 exposure. Therefore, estimation of TiO¬2 dietary intake and gut exposure is needed among a free-living U.S. population of adults with a wide variation of intakes.

Pre-clinical models show that greater TiO2 oral exposure may lead to impaired gut health through changes in gut bacterial content and function. TiO2 has been shown to damage intestinal cells where small doses of TiO2 caused changes in normal activity, but not damage to the cell's genetics. After very small particles of TiO2 are taken up by these intestinal cells, it causes mild toxicity and disruption of the cell's function. In addition, very small particles of TiO2 accumulate in intestinal cells and remodel the cell's community in the small intestine, suggesting these particles may get absorbed into the body's blood and general circulation. These results demonstrate that very small particles of TiO2 causes harmful changes to the intestinal cells, is absorbed by the intestinal cells, and once inside, can cause harmfulness and promote abnormal cellular function. There is an urgent need for studies in humans to determine whether high versus low level exposure to TiO¬2 is related to gut inflammation and disruption in gut function.

The current study will fill these research gaps by testing the hypothesis that long term dietary exposure of TiO2 is related to gut inflammation and disturbs gut bacteria in humans. This hypothesis will be tested for the first time via these specific aims: 1) to quantify dietary TiO2 exposure by estimating dietary intake and measuring the fecal output of TiO2 in 80 adults; 2) to establish the relationship of dietary TiO2 with gut bacteria and their activity; and 3) to determine whether dietary TiO2 exposure is related to gut inflammation and associated inflammatory pathways.

Inclusion criteria

• Healthy persons between the ages of 18 to 30 y.

Exclusion criteria

• <18 years and >30 years
• antibiotic use in the past 6 months
• laxative use in the past 30 days
• self-reported fever, cancer, or gastrointestinal disease (e.g., inflammatory bowel diseases, C. difficile infection
• use of selective serotonin reuptake inhibitors (SSRI's)
• use of non-steroidal anti-inflammatory drugs (NSAIDs) within 10 days
• daily use of proton pump inhibitors
• history of gastrointestinal alteration (e.g., appendectomy, gastric bypass surgery)
• pregnancy.