May 12, 2021

Cancer death rates have fallen dramatically in the United States. Factor in obesity, however — as researchers did at the University of North Carolina Gillings School of Global Public Health — and the picture changes.

In a study published May 10 in JAMA Network Open, researchers showed that obesity-related cancer deaths are improving, but at a slowing pace.

Based on mortality data for 50 million people, deaths from cancers not associated with obesity — that’s lung cancer and skin cancer, among others – are declining at a rate almost three times faster than cancers linked to obesity, such as stomach, colorectal, uterine, thyroid and postmenopausal breast cancer.

Dr. Hazel Hichols

Dr. Hazel Nichols

“These are cancers where we could see even larger mortality improvements with creative and practical tools to combat obesity,” said study senior author Hazel B. Nichols, PhD, associate professor in the Department of Epidemiology at the UNC Gillings School.

Most Americans weigh more than recommended and being overweight or obese puts them at risk for certain cancers 

Extra weight can lead to changes in the body that can contribute to cancer development, such as long-lasting inflammation and higher than normal levels of insulin and hormones that can fuel cell growth, according to the U.S. Centers for Disease Control and Prevention.

Measuring progress 

Cancer death rates are one of the best measures researchers use to track progress against cancer over time.  

The authors of this study set out to answer whether widespread obesity could stall progress against cancer the same way it has with heart disease. Improvements in heart disease mortality slowed after 2011, and obesity may have contributed to the deceleration. 

“What was puzzling was that we didn’t see the same pattern of slower improvements when looking at cancer overall, which is surprising because obesity contributes to both cancer risk and heart disease risk,” said Nichols, who studies cancer trends to improve decision-making in cancer care. “When we focused on the differences between obesity-related cancers and non-obesity related cancers, we saw that improvements for obesity cancers were not as impressive — consistent with the pattern for heart disease.” 

For example, the study showed that in 2011, 110 people out of 100,000 died from cancers not related to obesity. In 2018, the mortality rate for those cancers fell to 93.8 deaths per 100,00 people, representing a 2.29% annual decline.

During the same period, the decline for obesity-related cancers was much slower, changing from 58.4 to 54.9 deaths per 100,000 people, roughly a third the rate at .83% — of the decrease in non-obesity related cancers.

Additionally, obesity may be contributing to more of the cancer deaths in the U.S. The study reports that cancers not associated with obesity accounted for 66.8% of cancer deaths in 1999, decreasing to 62.6% in 2018.

Declines in cancer deaths are owed to fewer people smoking, along with better screening and treatments, according to the American Cancer Society.

Dr. Christy Avery

Dr. Christy Avery

Dr. Annie Green Howard

Dr. Annie Green Howard

But the findings by UNC researchers reinforce the effect of obesity on cancer. In addition to Nichols, the researchers include Christy Leigh Avery, PhD, an associate professor at Gillings School who specializes in cardiovascular epidemiology and a Carolina Population Center fellow, and Annie Green Howard, PhD, an associate professor in biostatistics at Gillings and a fellow at the Carolina Popular Center.

“Obesity is a risk factor for many, but not all, types of cancer,” Nichols said. “We need to make maintaining a healthy weight an obtainable goal for everyone in terms of safe public spaces, the availability and affordability of nutritious foods, and other structural factors. The good news is that if we’re able to make these changes as a society, we will be able to improve the health of a nation.”

The National Institutes of Health funded this study.

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