For every 300 mg increase in calcium from supplements was associated with a 9% reduction in risk, wrote NaNa Keum and her co-authors in the International Journal of Cancer.
Every 300 mg increase in total calcium was associated with a similar reduction in risk (8%), they added.
“Our findings have several important clinical and public health implications,” they explained. “First, according to the 2003 to 2006 National Health and Nutrition Examination Survey, a nationally representative cross-sectional survey in the U.S., median total calcium intake of adults aged over 50 years was approximately 650 mg/day for no calcium-supplement users and 1,000 mg/day for calcium-supplement users.
“As the benefit of calcium intake on CRC is expected to continue beyond 1,000 mg/day, not only non-supplement users but also supplement users may further reduce their CRC risk through additional calcium intake.”
“Second, while dairy products, especially milk, are the major sources of calcium in many countries, they are a substantial source of calories and contain potentially harmful factors such as saturated fat, hormones, and casein proteins. Since our analyses provide evidence for an equivalent benefit of dietary and supplementary calcium, the benefit of calcium on CRC risk may be obtained through supplements and non-dairy products fortified with calcium.”
The Boston-based scientists conducted dose-response meta-analyses of 15 studies involving 12,305 cases of colorectal cancer and calcium intakes ranging from 250-1,900 mg/day. The studies varied in duration from 3.3 to 16 years.
The data indicated that both total and supplemental calcium were associated with reductions in the risk of colorectal cancer.
“In conclusion, both dietary and supplementary calcium intake may continue to decrease colorectal cancer risk beyond 1,000 mg/day,” wrote Keum and her co-authors.
“RCTs of calcium supplements with at least 10 years of follow-up are warranted to confirm a benefit of calcium supplements on colorectal cancer risk.”
The main health benefit of calcium (in combination with vitamin D) has been for bone health, but papers published in journals such as JAMA, Heart, and the British Medical Journal have raised concerns that excess intake of the mineral may be related to adverse cardiovascular effects. (The plaques that form in diseased arteries are composed mostly of calcium.)
The literature, however, is contradictory, with Harvard Medical School researchers, for example, reporting no link between calcium supplements and an increased risk of artery calcification in November 2012 in the American Journal of Clinical Nutrition.
Moreover, a meta-analysis published in the Journal of Bone and Mineral Research this summer (doi: 10.1002/jbmr.2311) concluded that current evidence does not support the notion that calcium supplements increase the risk of heart disease in elderly women.
Source: International Journal of Cancer
2014, Volume 135, Number 8, Pages 1940-8, doi: 10.1002/ijc.28840
“Calcium intake and colorectal cancer risk: Dose-response meta-analysis of prospective observational studies”
Authors: N. Keum, D. Aune, D.C. Greenwood, W. Ju, E.L. Giovannucci