Calcium intake and colorectal cancer risk: Results from the nurses' health study and health professionals follow-up study.

The relationship between calcium intake and colorectal cancer (CRC) risk remains inconclusive. We conducted this study to evaluate whether the association between calcium intake and CRC risk differs by anatomic subsite and determine the dose-response relationship for this association, as well as assess when in carcinogenesis calcium may play a role. We assessed calcium intake every 4 years and followed 88,509 women (1980-2012) in the Nurses' Health Study and 47,740 men (1986-2012) in the Health Professionals Follow-Up Study. We documented 3,078 incident CRC cases. Total calcium intake (≥1,400 vs. <600 mg/d) was associated with a statistically significant lower risk of colon cancer (multivariable relative risk: 0.78, 95%CI: 0.65-0.95). Similar results were observed by different sources of calcium (from all foods or dairy products only). The inverse association was linear and suggestively stronger for distal colon cancer (0.65, 0.43-0.99) than for proximal colon cancer (0.94, 0.72-1.22, p-common effects  = 0.14). Additionally, when comparing different latencies, the overall pattern suggested that the inverse association appeared to be stronger with increasing latency and was strongest for intakes 12-16 years before diagnosis. Comparing total calcium intakes of ≥1,400 vs. <600 mg/d for intake 12-16 y before diagnosis, the pooled RR (95% CIs) of CRC was 0.76 (0.64-0.91). Higher calcium intake was associated with a lower risk of developing colon cancer, especially for distal colon cancer. Overall inverse association was linear and did not differ by intake source. Additionally, calcium intake approximately 10 years before diagnosis appeared to be associated with a lower risk of CRC.