N-
nitroso compounds (NOC) are potent animal
carcinogens and potential human
carcinogens. The primary source of exposure for most individuals may be endogenous formation, a process that can be inhibited by dietary
polyphenols. To estimate the risk of
gastric cancer (GC) in relation to the individual and combined consumption of
polyphenols and NOC precursors (
nitrate and
nitrite), a population-based case-control study was carried out in Mexico City from 2004 to 2005 including 257 histologically confirmed GC cases and 478 controls. Intake of
polyphenols,
nitrate and
nitrite were estimated using a food frequency questionnaire. High intakes of cinnamic
acids,
secoisolariciresinol and
coumestrol were associated with an approximately 50% reduction in GC risk. A high intake of total
nitrite as well as
nitrate and
nitrite from animal sources doubled the GC risk. Odds ratios around 2-fold were observed among individuals with both low intake of cinnamic
acids,
secoisolariciresinol or
coumestrol and high intake of animal-derived
nitrate or
nitrite, compared to high intake of the
polyphenols and low animal
nitrate or
nitrite intake, respectively. Results were similar for both the intestinal and diffuse types of GC. Our results show, for the first time, a protective effect for GC because of higher intake of cinnamic
acids,
secoisolariciresinol and
coumestrol, and suggest that these
polyphenols reduce GC risk through inhibition of endogenous nitrosation. The main sources of these
polyphenols were pears, mangos and beans for cinnamic
acids; beans, carrots and squash for
secoisolariciresinol and legumes for
coumestrol.