Effect of drinking water calcium, magnesium, and hardness on colorectal cancer mortality: A systematic review

Background and aim: This systematic review aimed to summarise findings from studies investigating the association between calcium, magnesium, and drinking water hardness and colorectal cancer mortality. Methods: A systematic literature search was conducted on PubMed, Scopus, and Web of Science databases. The work was carried out according to the Cochrane Handbook and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The protocol was registered in Open Science Framework (OSF) Registries (https://doi.org/10.17605/OSF.IO/5HEVS). Results: One hundred thirty-three records were identified, and at the end of the selection process, nine studies met the inclusion criteria. All the studies were conducted before 2011 in the same geographical area (Taiwan, China). All the studies suggested a protective effect of higher calcium concentration in drinking water towards colon cancer mortality, whereas the effects on rectal cancer mortality were mixed. High water hardness seems to be protective towards mortality from both cancer types. Conclusions: This systematic review found interesting results on the potential role of calcium-rich water in the management of colon cancer. These results, however, should be confirmed in novel, large and preferably longitudinal studies conducted in other parts of the world before drawing definitive conclusions.