Obesity slows progress against cancer deaths, study suggests

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.

"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, associate professor in the Department of Epidemiology at the UNC Gillings School of Global Public Health.

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

Extra weight can cause changes in the body that help lead to cancer, 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.

Study authors 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 non-obesity related cancers.

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

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

But the findings by the UNC researchers, which include Christy Leigh Avery, an associate professor at Gillings School of Global Public Health specializing in cardiovascular epidemiology and a fellow at the Carolina Population Center and Annie Green Howard, an associate professor in biostatistics at Gillings and fellow at Carolina Popular Center, reinforces the effect of obesity on cancer.

"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, availability and affordability of nutritious foods, and other structural factors. The good news in that is 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 the study.