Summary
This prospective cohort study of 21,977 Iowa women examined whether long-term exposure to nitrate in municipal drinking water increases cancer risk, hypothesising that nitrate reduction to carcinogenic N-nitroso compounds might elevate incidence. Overall cancer incidence showed no dose–response relationship with increasing water nitrate; however, positive associations emerged for bladder cancer (RR 1.0–2.83 across quartiles) and ovarian cancer (RR 1.0–1.84), whilst inverse associations were observed for uterine and rectal cancers, findings the authors note were largely unexpected.
Regional applicability
This study was conducted in Iowa, United States, where agricultural nitrate contamination of groundwater is a recognised public health concern distinct from current United Kingdom drinking water regulations, which enforce a stricter 50 mg/L (11.3 mg/L nitrate-nitrogen) limit. The findings are relevant to regions with similar intensive agricultural practices and nitrate-vulnerable groundwater, though the study's community-level exposure assignment (rather than individual consumption data) limits direct applicability to UK water quality monitoring and risk assessment frameworks.
Key measures
Municipal drinking water nitrate levels (quartiles: ≤0.36, 0.36–1.01, 1.01–2.46, >2.46 mg/L nitrate-nitrogen); cancer incidence by type; relative risks (RRs) adjusted for smoking, vitamin C and E intake, dietary nitrate, and water source.
Outcomes reported
Cancer incidence (3,150 cases) over 12 years (1986–1998) in relation to municipal drinking water nitrate levels (0.36–2.46 mg/L nitrate-nitrogen). The study examined associations between nitrate exposure and multiple cancer types, including bladder, ovarian, uterine, rectal, and common cancers.
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