The Obesity-Inactivity-Cancer Chain

Colorectal cancer risks increase with obesity and inactivity

(RxWiki News) The link between obesity and cancer is nothing new. Lack of regular exercise and cancer are also teammates. A new study has added some links to this chain of knowledge.

Researchers found that higher body mass index (BMI) was associated with a specific type of colorectal cancer. Physical activity decreased the risk of this cancer, which has a specific molecular signature.

These findings may assist in the development of solid ways to prevent cancer.

"Get off the couch and take part in activities you enjoy."

Shuji Ogino, MD, PhD, associate professor of pathology at Dana-Farber Cancer Institute, and colleagues looked at information about thousands of patients to better understand why exercise and maintaining a healthy weight decreases the risk of colorectal cancer.

Researchers focused on a molecule that plays a role in both obesity and cancer. This is the biomarker called CTNNB1.

The team analyzed data of nearly 150,000 men (45,000+) and women (100,000+) who participated in the Nurses' Health Study and the Health Professionals Study. The goal of the study was to see if obesity or exercise affected colorectal cancer according to CTNNB1 status.

Researchers assigned patients to one of two groups – CTNNB1-positive, meaning the patient had the molecule, or CTNNB1-negative.

A total of 2,263 people in the studies were diagnosed with colorectal cancer. Researchers were able to determine the CTNNB1 status of 861 study members – 54 percent were negative for CTNNB1 and 46 percent had the biomarker.

Researchers analyzed data from questionnaires participants completed every two years regarding their diet, physical activity, weight, smoking status, other lifestyle factors and cancer diagnoses in themselves or first-degree relatives.

Compared to men with BMIs in the 18.5–22.9 kg/m2 range, men with BMI of 27.5–29.9 kg/m2 or 30 kg/m2 had a 34 percent higher risk of CTNNB1-negative cancer.

Increasing activity was associated with a significantly lower risk of CTNNB1-negative cancer, but did not impact CTNNB1-positive cancer risks.

"Our results provide additional evidence for a causal role of obesity and a physically inactive lifestyle in a specific molecular subtype of colorectal cancer," Dr. Ogino said.

What does this mean for patients?

Dr. Ogino explained that if physicians could tell if a person was likely to develop CTNNB1-negative cancer, this individual could be urged to increase physical activity.

The CTNNB1 molecule could also become a target for new drugs to help prevent or treat these types of colorectal cancers.

Jim Crowell, owner and head trainer of Integrated Fitness in Pittsburgh, told dailyRx News, "I have seen people of all ages and ‘makes and models’ come in through my gym. It is almost without fail that as they begin to lose excess fat and live a more active and fit lifestyle, they have fewer trips to the doctor or the pharmacy due to sickness.

"Because of this and many other studies, I believe that an active lifestyle and a consistent focus on increasing health leads to markedly less long-term risk of dangerous diseases," Crowell said.

Dr. Ogino believes the study adds fuel to the growing understanding that one particular cancer has many different molecular patterns. So colorectal cancer, for example, is actually many different kinds of cancer – even though it is treated as a single disease.

As a result, Dr. Ogino called for more population-based studies that look at molecular differences in tumors “to facilitate integrative science and improve public health."

“In the future, we may be able to identify individuals who are susceptible to the development of CTNNB1-negative tumors, and lifestyle preventive measures can be taken. Thus, our findings may help us develop better cancer prevention strategies,” the authors concluded.

This study was published February 26 in Cancer Research, a journal of the American Association for Cancer Research. No conflicts of interest were disclosed.

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Review Date: 
February 26, 2013