Clinical trials find calcium / vitamin D may reduce colon cancer risk

Research findings presented at the American Association for Cancer Research meeting, held this year in San Diego, suggest that supplementing with vitamin D and calcium may reduce colon cancer risk, while consuming too much iron might increase it.

Veronika Fedirko of Emory University presented her team’s discovery that supplementing colorectal adenoma (polyp) patients with 2 grams calcium, 800 international units of vitamin D, or a combination of the two for six months was associated with an increase of Bax, a protein that controls apoptosis (programmed cell death), compared with placebo group levels. By increasing Bax levels in the colon’s mucosa, a greater number of precancerous cells (such as those that are found in polyps) may self-destruct. The trial found that the greatest increase in the ratio of Bax to Bcl-2 (an apoptosis inhibitor) occurred in the group that received both calcium and vitamin D.

“We were pleased that the effects of calcium and vitamin D were visible enough in this small study to be significant and reportable,” Dr Fedirko stated. “We will have to fully evaluate each marker’s strength as we accumulate more data.”

In another study presented at the AACR meeting, Emory University Rollins School of Public Health professor of epidemiology Robert Bostick, MD, MPH and colleagues found that individuals who consume high amounts of vitamin D and calcium had increased expression of E-cadherin, a calcium-dependent glycoprotein that moderates the movement and proliferation of colon cells. Loss of E-cadherin expression has been associated with the progression of cancer. The study involved the comparison of biopsy samples from individuals with and without sporadic colorectal adenoma, and is part of a larger effort to identify biomarkers for the development of colon cancer. “We want to have the equivalent of measuring cholesterol or high blood pressure, but for colon cancer instead of heart disease,” Dr Bostick remarked. “These measurements will describe the climate of risk in the colon rather than spotting individual tumors or cells that may become tumors.”

An additional abstract coauthored by Dr Bostick reported the finding in the same study population that high levels of iron are associated with a reduction in a protein known as APC needed to control cell growth. “Clinical implications of these findings, if confirmed, could include lowering iron intakes in adenoma patients to prevent adenoma recurrence or colorectal cancer,” the authors conclude.

The current studies contribute more evidence for a protective role for calcium and vitamin D in colorectal cancer. Dr Bostick’s team is involved in a ten year study at several centers which will evaluate the effects of increased calcium and vitamin D as well as biomarker-guided treatment on the recurrence of colon cancer.