Too Few Realize Obesity Can Cause Cancer

Editor's Note: The Children’s Health Matters blog is a space dedicated to sharing important new research, policy ideas, clinical findings and journalism on child health and development. It’s part of our effort to spur a conversation online and off that offers a rich and varied set of perspectives. As part of that mission, we’re excited to announce a new collaboration with Children’s Hospital Los Angeles. Once a month this blog will feature a new column with insights offered by two of the hospital’s leading community-based research teams.

The first of the two groups is made up of community-based researchers who are tackling pediatric health challenges stemming from obesity and diabetes. Children who develop Type II diabetes cycle through the stages of the disease far faster than adults. What are the economic, health and demographic consequences for a generation that may develop Alzheimer’s, Parkinson’s, glaucoma or circulatory issues at a far younger age? Our bloggers will discuss some of the latest prevention strategies and approaches.

Our other group of Children’s Hospital L.A. contributors is focused on severely ill children who are aging out of pediatric care and the services and benefits that formerly supported them. Researchers are seeing an uptick in severe illness and death among the population once these crucial benefits end. Our bloggers will share some the latest thinking about how to understand and improve the situation.

For our first installment in the series, Dr. Steven Mittelman, director of the Diabetes and Obesity Program at Children’s Hospital Los Angeles, explores the link between obesity and cancer. We welcome your ideas and comments.

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How is it possible that most people haven’t heard that obesity causes cancer? Everybody knows that smoking causes cancer, and that obesity causes heart disease, but even most doctors and scientists I speak to have no idea about the very large effect obesity has on cancer. Obesity causes approximately 90,000 cancer deaths per year in the United States, and Harold Varmus, director of the National Cancer Institute, has acknowledged that obesity is probably responsible for about 20% of all cancers in our country.

In a landmark paper published in the New England Journal of Medicine in 1993, Eugenia Calle and colleagues from the American Cancer Society found in a cohort of over 900,000 people followed over time, the most obese individuals had a 50% to 88% higher risk of dying from cancer than those who were lean[1]. What was surprising was the sheer number and variety of cancers associated with obesity — obese people were more likely to die from cancers of the blood, breast, colon, liver, kidney, and other sites.

In 2007, a study out of Children’s Hospital Los Angeles showed for the first time that obesity could also impact childhood cancer. In a relatively large group of over 5,000 children, Anna Butturini and colleagues showed that children who were obese at the time they were diagnosed with a high-risk form of the most common type of leukemia (acute lymphoblastic leukemia), had about a 50% higher chance of that disease coming back after treatment than lean patients. Not only did this open my eyes to the fact that obesity can impact cancer, but I decided then and there that I needed to figure out how obesity might make leukemia harder to cure.

What I have found over the last six years is an exploding scientific field with many groups trying to understand how obesity impacts cancer. Most of this work looks at adult cancers, where researchers have identified possible mechanisms linking obesity to a specific cancer; however, there are a lot of contradictory results, and it is difficult thus far to identify one or two unifying themes explaining how obesity causes cancer and worsens cancer prognosis. Since this research field is still relatively young, I am optimistic that breakthroughs will be made that will help us identify and reverse some of the major factors linking obesity to cancer.

At Children’s Hospital Los Angeles, we’re exploring how the growing epidemic of childhood obesity might actually lead to a worsening in cancer mortality in kids. In my laboratory, we’ve found that mice develop leukemia earlier when they are made obese by a high fat diet. We also discovered that leukemia cells are actually attracted to fat tissue, and that fat cells can protect leukemia cells from a variety of chemotherapies. One of the ways fat cells protect leukemia cells is by providing them with important fuels, which helps the leukemia grow and divide even during chemotherapy treatment. So far, these findings have uncovered more questions than answers, but as we are able to hone in on the actual mechanisms of how obesity worsens leukemia, we hope to identify potential strategies to block these effects.

So what do I tell cancer patients who are obese? It is still too early to say whether going on a diet will help once you already have cancer. However, given the number of physical, physiological, and psychological benefits, I recommend a healthy, balanced diet and physical activity, even during cancer treatment. Healthy diet and exercise are some of the things that patients and their families can do that might actually help with the treatment of their disease. Of course, patients and families should always discuss with their oncology doctor if they are thinking of more intense diets or strenuous exercise.

But even more importantly, these findings should be a call to arms for our communities. Obesity is the leading preventable cause of disease and death in the U.S. We should take a lesson from our success in reducing lung cancer with tobacco reduction programs. Public awareness campaigns, excise taxes, and legislation limiting opportunities to smoke all contributed to a reduction in smoking, and prevented in excess of 750,000 lung cancer deaths. But those changes were only possible once the public really understood the impact of smoking. The American Institute for Cancer Research estimates that about one-third of cancers could be prevented by beneficial lifestyle changes such as eating a healthier diet and increasing activity.

It is possible for kids to lose weight and become healthier, but it is not easy. Our environment promotes obesity, with advertising promoting unhealthy foods, less physical activity in school, and neighborhoods without enough safe parks and walkable space. It takes an extra effort to make healthy choices in these environments, but it is definitely possible. Setting up regular exercise with friends and family, cooking at home and eating together, or enrolling in a sports program are ways to make a real change in your lifestyle. The patients that I have seen who are successful in improving their weight and their health are the ones who are able to take control of their own environment. I hope that increasing awareness will lead to positive changes in the environments of all of our children, and help protect them from diabetes, heart disease, and cancer.

The image by colros via Flickr has been modified.