Objective Although evidence suggests an inverse association between calcium intake and the risk of colorectal cancer, the mechanisms remain unclear. The calcium-sensing receptor (CASR) is expressed abundantly in normal colonic epithelium and may influence carcinogenesis. We hypothesized that calcium intake might be associated with lower risk of CASR-positive, but not CASR-negative, colorectal cancer. Design We assessed tumour CASR protein expression using immunohistochemistry in 779 incident colon and rectal cancer cases that developed among 136 249 individuals in the Nurses' Health Study and Health Professionals Follow-Up Study. Duplication method Cox proportional hazards regression analysis was used to assess associations of calcium intake with incidence of colorectal adenocarcinoma subtypes by CASR status. Results Total calcium intake was inversely associated with the risk of developing colorectal cancer (p trend =0.01, comparing ≥1200 vs <600 mg/day: Multivariable HR=0.75, 95% CI 0.60 to 0.95). For the same comparison, higher total calcium intake was associated with a lower risk of CASR-positive tumours (p trend =0.003, multivariable HR=0.67, 95% CI 0.51 to 0.86) but not with CASR-negative tumours (p trend =0.67, multivariable HR=1.15, 95% CI 0.75 to 1.78; p heterogeneity =0.06 between the CASR subtypes). The stronger inverse associations of calcium intake with CASR-positive but not CASR-negative tumours generally appeared consistent regardless of sex, tumour location and source of calcium. Conclusions Our molecular pathological epidemiology data suggest a causal relationship between higher calcium intake and lower colorectal cancer risk, and a potential role of CASR in mediating antineoplastic effect of calcium.
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