Associations between calcium and magnesium intake and the risk of incident gastric cancer: A prospective cohort analysis of the National Institutes of Health-American Association of Retired Persons (NIH-AARP) Diet and Health Study.

Gastric cancer remains a leading cause of cancer-related mortality. Identifying dietary and other modifiable disease determinants has important implications for risk attenuation in susceptible individuals. Our primary aim was to estimate the association between dietary and supplemental intakes of calcium and magnesium and the risk of incident gastric cancer. We conducted a prospective cohort analysis of the National Institutes of Health-American Association of Retired Persons Diet and Health Study. We used Cox proportional hazard modeling to estimate the association between calcium and magnesium intakes with risk of incident gastric adenocarcinoma (GA) overall and by anatomic location, noncardia GA (NCGA) and cardia GA (CGA). A total of 536,403 respondents (59% males, 41% females) were included for analysis, among whom 1,518 incident GAs (797 NCGA and 721 CGA) occurred. Increasing calcium intake was associated with lower risk of GA overall (p-trend = 0.05), driven primarily by the association with NCGA, where the above median calcium intakes were associated with a 23% reduction in risk compared to the lowest quartile (p-trend = 0.05). This magnitude of NCGA risk reduction was greater among nonwhite ethnic group and Hispanics (hazard ratio [HR] 0.51, 95% confidence interval [CI]: 0.24-1.07, p-trend = 0.04), current/former smokers (HR 0.58, 95% CI: 0.41-0.81), obese individuals (HR 0.54, 95% CI: 0.31-0.96) and those with high NCGA risk scores (HR 0.50, 95% CI: 0.31-0.80). Among men only, increasing magnesium intake was associated with 22-27% reduced risk of NCGA (p-trend = 0.05), while for the cohort, dietary magnesium intake in the highest vs. lowest quartile was associated with a 34% reduced risk of NCGA (HR 0.66, 95% CI: 0.48-0.90). These findings have important implications for risk factor modification. Future investigations are needed not only to confirm our results, but to define mechanisms underlying these associations.