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Cancer ResearchSurvivorship

The Link between Obesity and Cancer

Obesity is associated with about 40% of cancers in the United States. This link is strongest in several types of cancer, including kidney, gastric, pancreatic, endometrial, and esophageal cancer. Significant weight reduction may help to reduce the risk for cancer.
April 2019 Vol 5 No 2
Kelsey Moroz

A new study funded by the American Cancer Society and the National Cancer Institute shows that although the number of deaths from cancer in the United States has decreased overall, obesity-related cancer deaths are on the rise, based on data from 1995 to 2014 in the United States.1 In fact, all the types of cancer that show an increase in death rates are the ones that have been shown to be associated with obesity.

The increase is particularly evident among younger adults under age 50, especially related to colorectal cancer, uterine cancer, gallbladder, kidney, pancreatic, and thyroid cancer. For example, according to that new study, the rate of colorectal cancer has increased in younger adults under age 50 in the United States, which “could in part reflect the obesity epidemic,”1 the study authors note.

Ken Thorpe, PhD

Cancer and Obesity

According to the National Cancer Institute, although the exact reasons why obesity increases the risk for cancer is not fully understood, and the exact explanation may be different from what is currently being assumed, there is good evidence to link excess body weight with increased risk for having cancer.

This could in part be because obese adults are at risk for several medical conditions that are linked to low-level chronic local inflammation in the body. This low-grade inflammation can cause different health problems, including DNA damage over time, which is a significant risk factor for cancer.

Most people know that obesity can increase the person’s risk for chronic diseases such as diabetes, stroke, or high blood pressure. However, the direct link between obesity and cancer is less known.

“Obesity is associated with about 40% of total cancers in the country. So nearly 40% of all cancer cases are potentially preventable, because those are the ones that are linked to overweight and obesity,” Ken Thorpe, PhD, Chairman of the Partnership to Fight Chronic Disease, said in an interview.

Despite the evidence that obesity can severely affect people’s overall health, the number of obese Americans has nearly doubled since 1990, and with this increase, the number of obesity-­related cancer deaths has also risen.

“The incidence of cancer among obese patients really hasn’t changed that much. It’s just that we have a lot more obese adults,” said Dr. Thorpe. “I don’t think most people really understand the cancer risk that they face being obese.”

For example, obesity is a risk factor for gallstones, and people with gallstones are at an increased risk for gallbladder cancer.

People with chronic ulcerative colitis or with hepatitis are at an increased risk for different types of liver cancer.

Breast cancer, endometrial (uterine) cancer, and ovarian cancer are some of the cancers thought to be associated with high amounts of estrogen, which is produced by fat tissue.

Obese people with high levels of insulin and insulin-like growth factor-1 are at increased risk for colon, kidney, prostate, and endometrial cancers.

As shown in the Table, 13 types of cancer are linked to obesity, according to the National Cancer Institute.

thelinkbetween_figure1

Cancer Screening

Although about 630,000 cases of cancer in the United States each year are linked to people who are overweight or obese, the overall rate of cancer deaths has gone down.

In the past 2 decades, the combined rate of cancer deaths for men and women decreased by about one-quarter (26%) from its peak in 1991, according to the results of the new study.1 This has meant that nearly 2.4 million cancer-related deaths have been prevented during that period.

The study authors attributed the decrease in the overall cancer-related death rate, in part, to early detection and lower rates of smoking in the United States.

Dr. Thorpe thinks that these same methods—earlier detection through better screening methods, as well as public awareness highlighting the link between cancer and obesity—may be the key to lowering the number of cancer deaths linked to obesity.

“I think that the Affordable Care Act made a big difference, because all cancer detection screenings now have to be provided in private health insurance plans with no cost-sharing, so they’re free,” said Dr. Thorpe.

“Populations that are at-risk, and that includes overweight and obese adults, should be even more vigilant on going through the whole range of age appropriate cancer and cardiovascular risk screening, glucose tests, blood testing, and so on,” he advised.

Weight Loss and Cancer Prevention

Although better cancer screening and early detection have been shown to influence cancer death rates, Dr. Thorpe believes that prevention will play an equally large part in lowering the number of obesity-related cancer deaths.

“To the extent that we can get adults involved in intensive diet, exercise, nutrition programs, and lifestyle interventions that result in weight loss or prevent weight gain, that’s a very good strategy for improved cardiovascular health and improved odds of not having cancer,” he said.

In April 2018, Medicare launched a new intensive lifestyle program for adults with pre-hypertension and overweight adults, with the goal of helping people to achieve 5% to 7% weight loss.

The Medicare Diabetes Prevention Program has the potential to reduce the number of new cases of diabetes and heart disease in the United States, and potentially cancers as well, Dr. Thorpe said.

The increased risk of cancer associated with type-2 diabetes and cardiovascular (heart) disease is clear, according to Dr. Thorpe. He said that it is common to see patients who have all 3 conditions—type-2 diabetes, heart disease, and some form of cancer.

“If you look at obese adults, there’s like a constellation of chronic illnesses that put you at increased risk,” Dr. Thorpe said. “Type-2 diabetes is very common. If you have type-2 diabetes you’re twice as likely to have some type of cardiovascular disease, and you also are likely to have some form of cancer,” he added.

The challenge with the new Medicare program will be to get people to become aware of it, and to get eligible people to enroll and stay enrolled, said Dr. Thorpe.

The program includes a 16-week class that will provide in­formation about diet, exercise, nutrition, behavioral changes, setting goals, and accepting the goal of completing 150 minutes of physical activity a week.

Dr. Thorpe hopes that this program will eventually spread to private health insurance plans that will cover this program for younger people not covered by Medicare, so they could also take advantage of this weight-loss program.

Reference

  1. Sung H, Siegel RL, Rosenberg PS, Jemal A. Emerging cancer trends among young adults in the USA: analysis of a population-based cancer registry. Lancet Public Health. 2019;4(3):e137-e147.

Key Points

  • Although the number of deaths from cancer in the United States has decreased overall, obesity-related cancer
    deaths are on the rise
  • The link between obesity and cancer is often overlooked
  • Obesity is associated with about 40% of total cancers in the country, meaning that nearly 40% of all cancer cases are potentially preventable
  • The number of obese Americans has nearly doubled since 1990
  • Some types of cancer—including esophageal, gastric, kidney, liver, pancreatic, and uterine cancers—are more strongly linked to being obese than other cancers
  • Obese and overweight adults should be especially vigilant about age-appropriate screening for cancer and heart disease, including glucose tests and blood tests
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Last modified: May 14, 2019

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