Does high calcium consumption prevent colon cancer? The question has been a matter of much debate in recent years, as several large trials have yielded conflicting results. Now scientists at the Vanderbilt University School of Medicine in Nashville, Tenn., believe they might have the answer: Yes and no, depending upon your genes.
A study of nearly 6,000 people found that those with at least one of two common gene variants that impair calcium absorption in the kidney greatly reduced their risk of developing pre-cancerous colorectal adenomas when they ate lots of calcium-rich foods or took supplements. In people with no variants, calcium intake had no impact on risk.
Presented at the American Association of Cancer Research annual meeting in April, the research bolsters the burgeoning notion that nutritional needs vary based on individual genetics, and its authors hope it may lead to new tests to determine who needs to up their calcium intake.
We asked lead author Xiangzhu Zhu, MD, staff scientist in the Division of Epidemiology at Vanderbilt-Ingram Cancer Center about the study.
Natural Foods Merchandiser: What prompted you to do this study?
Xiangzhu Zhu: Previous studies suggested that a high intake of calcium (through food or supplements) was associated with a reduced risk of colorectal adenomas (precancerous lesions). But data from the Women’s Health Initiative (in which 36,000 women supplemented with 1,000 mg of calcium daily for seven years) did not support those findings. Previous studies also indicate there is a substantial inter-individual variation in the ability to absorb calcium, which is mostly attributed to genetic variation. We hypothesized that some of the inconsistency in previous studies was because of interactions between calcium and genetic polymorphisms.
NFM: How did you do it?
XZ: We looked at nearly 6,000 people who participated in the Tennessee Colorectal Polyp Study (1,818 who had tested positive for precancerous lesions; 3,992 who had not). We conducted a food frequency questionnaire to determine calcium intake and collected blood samples for genetic analysis. We looked at 14 genes related to calcium absorption.
NFM: What did you find?
XZ: We found that high-level calcium intake was associated with a 39 percent reduced risk of colorectal adenoma in people with variations in the gene KCNJ1 or the gene SLC12A1. In people with variations in both genes, high-level calcium intake was associated with a 69 percent reduction. The corresponding reduction in risk for advanced or multiple adenomas was
89 percent in those with genetic changes in both genes.
NFM: How common are these genetic variations?
XZ: Fifty-two percent of the study population carried genetic changes in at least one of the two genes and 13 percent carried changes in both. (Those with these gene variations are believed to have trouble absorbing calcium.)
NFM: Why is this study important?
XZ: Our results may provide one possible explanation for the inconsistency in previous studies. If confirmed in future studies, our findings will be critical for the development of new personalized prevention strategies for colorectal cancer. Despite increased screening via colonoscopy, colon cancer remains the second leading cause of cancer death in the United States.
NFM: For now, what is the take-home message for consumers?
XZ: Calcium can reduce risk of colorectal adenoma. Be sure you are getting 1,000 to 1,300 mg per day.