Vanessa Benham

for the Lansing State Journal

You probably know smoking causes cancer, maybe even that it's the leading preventable cause of cancer.

You might not know the second leading cause of cancer, because scientists have only recently made the connection.

It's obesity.

Researchers have been investigating a link between obesity and cancer for more than 15 years, but that link was only established conclusively in the past few years.

While public health officials have programs that address both obesity and cancer prevention, they haven’t tailored programs to specifically address obesity as a cancer risk factor.

They’ll have to.

Because of decreasing smoking rates and increasing obesity rates, obesity is predicted to surpass smoking as the No. 1 preventable cancer risk factor within the next two decades.

It’s already a public health concern in Michigan, which has the 10th highest adult obesity rate in the nation.

More than 32% of the state’s population is obese. That rate was as low as 25% in 2003. It has been rising steadily.

As it does, obesity-associated cancers are expected to increase. And the risk, at least according to some studies, is higher for African Americans.

“The risks for certain obesity-related cancers in younger people is higher in today’s generation of young people than it was a couple generations ago,” said Kristen Sullivan, director of nutrition and physical activity for the American Cancer Society. “We don’t know exactly where the risk is coming from, but a probable explanation is that we’re starting to see the results of the obesity epidemic.”

Doctors and researchers have made immense progress in treating cancer over the past three decades. A rising tide of obesity-related cancers could roll back some of those gains, “which would have critical implications for the health care systems.” Sullivan said.

“Right now, we are seeing a year-after-year decline in overall cancer rates and cancer death rates, and that’s been happening since 1991,” she said. “If that stops declining and (starts) going up, more people getting cancer, more people dying from cancer starting at a younger age, that would tax the health care system enormously.”

Obesity linked to 13 kinds of cancer

The first large-scale study to characterize obesity’s association with cancer was published in 2003. It was an extensive investigation of the relationship between body-mass index and the risk of death from cancer.

Beginning with over a million participants in 1982, the study spanned 16 years, and it showed an increase in body weight was associated with increased death rates due to cancer.

“As of right now, excess bodyweight or obesity are linked to 13 different types of cancer," Sullivan said, “and probably more cancer types will emerge as we continue to do more research."

Among those linked to obesity are ovarian, thyroid, uterine, pancreatic, colon and postmenopausal breast cancer.

Researchers are still working to understand exactly why. The relationship is complex, and experts are investigating a number of possible mechanisms.

One likely culprit? Belly fat

Many believe the link lies somewhere in the changes that happen in belly fat, what’s known as visceral adipose tissue in the abdomen.

Belly fat is more than just an energy store. It produces hormones and factors important for a person’s health. However, having too much fat can increase or decrease the amount of hormones, proteins and growth factors produced, which collectively increases health risks.

“There are a number of different processes in the body that are related to excess body weight that are probably contributing to cancer risk.” Sullivan said, “They [can] impact levels of certain hormones like insulin or estrogen. And we know of those hormones (that) elevated levels can increase risk for certain types cancers.”

Changes in the belly fat of obese individuals are likely connected to many of the other serious health conditions associated with obesity, including cardiovascular disease, type II diabetes and metabolic syndrome, which is a combination of high blood pressure, high blood sugar, excess belly fat and abnormal cholesterol levels.

The obesity epidemic is changing the way we look at these diseases.

Obesity, type 2 diabetes and cancer

Take, for instance, type 2 diabetes, which is strongly associated with obesity. In many cases, the problem isn’t that the body isn’t making enough insulin, a hormone that regulates sugar in the blood, but that the body doesn’t recognize the insulin it’s making.

“For type II, you actually see higher insulin production, higher levels in the blood,” said Dr. Cathy Jen, a professor in the Department of Nutrition and Food Science at Wayne State University whose research focuses on obesity and chronic disease.

And insulin resistance is a potential cause of cancer, she said. High insulin and insulin resistance will promote the production of a hormone called insulin-like growth factor 1, which regulates cell growth on the one hand, but can also stimulate the growth of cancer cells.

But the relationship between obesity and cancer isn’t that simple.

Scientists have shown hormone production and inflammation can also contribute to cancer formation, and researchers still do not know precisely how obesity causes cancer.

It’s not all about weight loss

You might assume the solution to the obesity epidemic would come down to losing weight.

Weight loss doesn’t hurt, but increasing physical activity and healthy eating improves health outcomes, whether you lose weight or not.

“It is the sedentary lifestyle that is more detrimental than not being physically active.” Jen said, “increase of physical activity even without body weight loss will improve insulin sensitivity, reduce insulin resistance and that will reduce insulin-like growth factors and that will reduce the stimulation for cancer growth.”

Minorities have higher obesity, cancer rates

Studies have shown that the environment plays a big role in promoting or combating obesity.

“In Detroit, for most people, the public transportation is not great. If they don’t have a car they cannot go to well-stocked supermarkets,” said Jen.

“So people without cars just go to the corner stores or gas stations. And what kind of products do they sell there? High-fat, high-calorie chips, long shelf life type of products, so people are more likely to consume high fat, high sugar, high-salt, and high-calorie products.”

“At the same time the walkability in Detroit, for inner cities, is low because people are afraid to walk.” Jen said.

It adds up to huge health disparities. And, for reasons bound up with issues of race and poverty and how both affect where people live, those disparities fall disproportionately on minorities.

“In inner cities like Detroit, the minority population has higher obesity rates and have higher cancer rates.” Jen said.

No big policy changes yet

The discovery of the obesity-cancer link is too new to have led to big policy changes.

Which is part of the reason why programs meant to combat obesity in Michigan fall under the cardiovascular branch of the state Department of Health and why the cancer division doesn’t directly address the obesity-cancer link

“Our section will work on promoting cancer awareness and prevention,” said Courtney Cole, the cancer prevention consultant at the health department. “We don’t work specifically on any programs that address obesity, but a lot of the programs we do offer focus on those risk factors such as diet and physical activity, and we do have direct service programs within our section.

Michigan’s health department was already treating obesity as a public health issue, working from the notion that obesity is not just a result of individual choices, but also a product of environment, of access to transportation and healthy food and places to exercise.

“Our work is framed around changes to policy and changes to the environment,” changes to the system that will support healthy eating and physical activity, said Gwen Imes, the unit manager for the Nutrition, Physical Activity, and Obesity Program of the Michigan Department of Health and Human Services.

Changing the environment

“Let’s say the community has a city park, but the park doesn’t have good lighting or the park doesn’t have any benches for people to sit down or it’s not safe. So we might engage law enforcement to work with us on a community level. Those are considered environmental changes, and, by making those changes, then we can say ‘OK, for those people in that area they can be physically active if that’s their choice.”

The program is also working with “people who specialize in developing biking paths and connecting trails and make it not only accessible but to make it safe for people to bike and walk.” said Loren Disha, a consultant for the Obesity Prevention Program. “We are improving parks and connecting them.” Making parks accessible and safe increases the physical activity of a city’s residents.

They’re also working to expand access to fresh fruits and vegetables.

“We fund work that makes fresh fruits and vegetables available in corner stores,” Disha said, “so that people who don’t have access to grocery stores or farmers markets are still having access to fresh fruits and vegetables.”

“We recognize that people don’t have the same starting place, so we want to make sure that everyone has an opportunity”

Fresh veggies at Quality Dairy

One of the first corner store projects began in Lansing in 2006.

“We convinced Quality Dairy,” said Peggy Vaugh-Payne, the executive director for the Northwest Initiative, a non-profit organization that works to strengthen and sustain healthy communities in the north and west sides of Lansing. “We started with one right on Pine and Saginaw.”

“We went from one store the first year to four stores a year and a half later, to 11 stores.” Vaughn-Payne said. “So obviously it worked out.”

Through the project, the corner stores stocked fruits and vegetables, increasing access for people in the surrounding neighborhoods.

But without the Northwest Initiative facilitating the program, it ended.

“The core of Lansing doesn’t have, and hasn’t had for 25 years now, a full-service grocery store,” Vaughn-Payne said.

A Meijer-owned store is set to open in the 600 block of East Michigan Avenue but not until 2020.

And so Northwest Initiative sets up shop in the basement of the First Presbyterian Church on North Ottawa Street every Thursday for their Emergency Food Distribution events.

Additionally, Kevin Kortas, the outreach manager at Northwest Initiative, and Vaughn-Payne piloted a new distribution method in the form of a mobile farmers market last summer to increase access to healthy options like fruits and vegetables.

“Every community that we went to said essentially the same thing of ‘we would not have been able to get to the grocery store to select these products without you being here,’” Kortas said. “Time and time and again that was the story we heard.”

How much weight do I need to lose

The relationship between obesity, healthy lifestyle and the environment is complex and not fully understood.

But, for those who want to reduce their cancer risk, “Physical activity in and of itself is an amazing thing to for your health and to reduce cancer risk, even if it doesn’t necessarily result in weight loss” Sullivan said.

Reducing your risk of cancer lies more with living a healthy lifestyle than the number on a scale.

In the meantime, experts say, the standard advice on diet and exercise applies: stay active, don't take in more calories than you burn through activity, choose whatever healthy diet you can stick with.

“It really doesn’t matter if you do high-fat or low-fat, high-carb or low-carb diet,” Jen said. “It doesn’t matter. The key point is to reduce caloric intake and the longer you stick to the diet the better the outcome.”

Vanessa Benham is a doctoral student in the Department of Pharmacology and Toxicology at Michigan State University. Reporting on this story was supported, in part, by a grant from the Science and Society at State program at MSU.