Weight and Activity Linked to Specific Colorectal Cancer
Having excess body fat is linked to increased risk of colorectal cancer; being active decreases the risk. Now a study suggests obesity and inactivity especially affect people with a certain type of cancer, a finding that provides insights into the possible different types of colorectal cancer and prevention strategies.
The study, published in Cancer Research, focused on a molecule called CTNNB1. The CTNNB1 gene makes a protein called beta-catenin, which is involved with cell signaling. Previously, the researchers found that mutations in this gene link to metabolic disease, obesity and increased colorectal cancer risk.
The researchers used data from two large studies that had began collecting lifestyle data in 1986 (for men) and 1976 (for women), respectively. They then looked for CTNNB1 expression among 861 of the participants who had developed colorectal cancer. Slightly over half – 54 percent – were CTNNB1-negative; they did not express the molecule.
For men who had CTNNB1-negative tumors, the higher their BMI the greater their risk. There was a 41 percent increased risk for every 5 increments in BMI. That translates to a 5’5” man (or woman) who weighed 150 pounds (BMI 25) gaining 30 pounds (BMI 30). There was no link between greater BMI and those who tested positive for CTNNB1.
Increasing exercise was also associated with a decreased risk of colorectal cancer among those who were only CTNNB1-negative. The findings were true for both men and women.
There are several possible mechanisms that could explain why high BMIs and low physical activity may link to this specific cancer, note the authors, but more studies are needed.
Source: Ogino S et al. "Prospective Analysis of Body Mass Index, Physical Activity, and Colorectal Cancer Risk Associated with B-Catenin (CTNNB1) Status. Cancer Research." Published online first on February 26, 2013.