N-
nitroso compounds (NOCs) are a class of chemical
carcinogens found in various environmental sources such as food,
drinking water, cigarette
smoke, the work environment, and the indoor air population. We conducted a systematic review and meta-analysis to investigate the links between
nitrate,
nitrite, and NOCs in food and water and the risk of gastrointestinal (GI)
cancers, including
esophageal cancer (EC),
gastric cancer (GC),
colorectal cancer (CRC), and
pancreatic cancer (PC). A systematic search of the literature in Scopus, PubMed, Google Scholar, Web of Science, ScienceDirect, and Embase was performed for studies on the association between NOCs in
drinking water and food sources and GI
cancers. Forest plots of relative risk (RR) were constructed for all the
cancer sites and the intake sources. The random-effects model was used to assess the heterogeneity between studies. Forty articles were included after removing duplicate and irrelevant articles. The meta-analysis indicated that the intake of high dose vs. low dose of these compounds was significantly associated with the overall GI
cancer risk and
nitrite (RR = 1.18, 95% CI = 1.07-1.29), and
N-nitrosodimethylamine (NDMA) (RR = 1.32, 95% CI = 1.06-1.65). We found that dietary
nitrite intake increased GC (RR = 1.33, 95% CI = 1.02-1.73), and EC (RR = 1.38, 95% CI = 1.01-1.89). Additionally, dietary NDMA intake increased the risk of CRC (RR = 1.36, 95% CI = 1.18-1.58). This meta-analysis provides some evidence that the intake of dietary and water
nitrate,
nitrite, and NOCs may be associated with GI
cancers. In particular, dietary
nitrite is linked to GC and EC risks and dietary NDMA intake is associated with CRC.