The Impact of Exposure to Hexavalent Chromium on the Incidence and Mortality of Oral and Gastrointestinal Cancers and Benign Diseases: A Systematic Review of Observational Studies, Reviews and Meta-Analyses

Background: Limited evidence suggests a possible connection between natural or occupational exposure to chromium and an increased risk of gastrointestinal cancer. The main objective of this study is to investigate the literature regarding chromium exposure and gastrointestinal health issues (i.e., cancer). Methods: A systematic literature search was performed using PubMed, Google Scholar and ScienceDirect. Included observational studies were assessed for their risk of bias. Results: 16 observational studies and 7 reviews and meta-analyses met the inclusion criteria. Most of the studies investigated gastric and hepatocellular cancer, followed by colorectal, oral, esophageal and pancreatic cancer. There is a limited amount of evidence regarding non-malignant gastrointestinal diseases. Chromium exposure is suspected to increase gastric and colorectal cancer risks. We did not find any convincing indications for increases in oral, esophageal and hepatocellular cancer. Pancreatic, gallbladder and extrahepatic bile ducts carcinogenesis is likely not associated with chromium exposure. Conclusion: We found weak evidence that chromium exposure is associated with gastric and colorectal cancer. Our review also highlights the existing controversial evidence regarding oral, esophageal and hepatocellular cancer, as well as the gap in studies investigating small intestinal cancer and non-malignant gastrointestinal health issues.